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  1. Guidance Documents (Medical Devices and Radiation-Emitting Products)

Cyclosporine and Tacrolimus Assays - Class II Special Controls Guidance Document for Industry and FDA

Document issued on: September 16, 2002

This document supersedes:

  • Class II Special Controls Guidance Document: Cyclosporine and Tacrolimus Assays; Draft Guidance for Industry and FDA, dated February 21, 2002; and
  • Guidance Criteria for Cyclosporine PMA's," dated January 24, 1992

U.S. Department of Health and Human Services
Food and Drug Administration
Center for Devices and Radiological Health

Chemistry and Toxicology Branch
Division of Clinical Laboratory Devices
Office of Device Evaluation



Public Comment

Comments and suggestions may be submitted at any time for Agency consideration to Dockets Management Branch, Division of Management Systems and Policy, Office of Human Resources and Management Services, Food and Drug Administration, 5630 Fishers Lane, Room 1061, (HFA-305), Rockville, MD, 20852. When submitting comments, please refer to the exact title of this guidance document. Comments may not be acted upon by the Agency until the document is next revised or updated.

For questions regarding the use or interpretation of this guidance contact Avis Danishefsky at 301-796-6142 or by email avis.danishefsky@fda.hhs.gov.

Additional Copies

Additional copies are available from the Internet. You may also send an e-mail request to CDRH-Guidance@fda.hhs.gov to receive a copy of the guidance. Please use the document number 1380 to identify the guidance you are requesting. 

Table of Contents

1. Introduction

2. Background

3. The Content and Format of an Abbreviated 510(k) Submission

4. Scope

5. Risks to Health

6. Performance Characteristics

7. Labeling

8. New Instrument Applications

9. References

Class II Special Controls Guidance Document:

Cyclosporine and Tacrolimus Assays; Guidance for Industry and FDA


1. Introduction

This guidance was developed as a special control guidance to support the reclassification of cyclosporine and tacrolimus assays into class II. The device is intended to quantitatively determine cyclosporine or tacrolimus concentrations as an aid in the management of transplant patients receiving therapy with these drugs. This guidance will be issued in conjunction with a Federal Register notice announcing the reclassification of this device type.

FDA is taking this action after reviewing reclassification petitions from industry for cyclosporine test systems. The agency is including tacrolimus test systems in the reclassification because of the similarities between these two test systems in terms of indications for use, assay technologies, potential risks and considerations for demonstrating performance characteristics. This guidance document replaces the guidance document "Guidance Criteria for Cyclosporine PMA's" issued January 24, 1992.

Following the effective date of this final reclassification rule, any firm submitting a 510(k) premarket notification for a cyclosporine and tacrolimus assays will need to address the issues covered in the special control guidance. The firm must show that its device addresses the issues of safety and effectiveness identified in this guidance, either by meeting the recommendations of this guidance or by some other means that provides equivalent assurances of safety and effectiveness.

2. Background

FDA believes that special controls, when combined with the general controls, will be sufficient to provide reasonable assurance of the safety and effectiveness of cyclosporine and tacrolimus assays. Thus, a manufacturer who intends to market a device of this generic type should (1) conform to the general controls of the Federal Food, Drug & Cosmetic Act (the Act), including the premarket notification requirements described in 21 CFR 807 Subpart E, (2) address the specific risks to health associated with cyclosporine and tacrolimus assays identified in this guidance and, (3) obtain a substantial equivalence determination from FDA prior to marketing the device, unless exempt from the premarket notification requirements of the Act (refer to 21 CFR 807.85).

This special control guidance document identifies the classification regulations and product codes for the cyclosporine and tacrolimus assays (Refer to Section 4 – Scope). In addition, other sections of this special control guidance document list the risks to health identified by FDA and describe measures that, if followed by manufacturers and combined with the general controls, will generally address the risks associated with these cyclosporine and tacrolimus assays and lead to a timely premarket notification [510(k)] review and clearance. This document supplements other FDA documents regarding the specific content requirements of a premarket notification submission. You should also refer to 21 CFR 807.87 and other FDA documents on this topic, such as Premarket Notification 510(k).

Under "The New 510(k) Paradigm - Alternate Approaches to Demonstrating Substantial Equivalence in Premarket Notifications; Final Guidance1," a manufacturer may submit a Traditional 510(k) or has the option of submitting either an Abbreviated 510(k) or a Special 510(k). FDA believes an Abbreviated 510(k) provides the least burdensome means of demonstrating substantial equivalence for a new device, particularly once a special controls guidance document has been issued. Manufacturers considering modifications to their own cleared devices may lessen the regulatory burden by submitting a Special 510(k).

1 The New 510(k) Paradigm

The Least Burdensome Approach

The issues identified in this guidance document represent those that we believe need to be addressed before your device can be marketed. In developing the guidance, we carefully considered the relevant statutory criteria for Agency decision-making. We also considered the burden that may be incurred in your attempt to comply with the statutory and regulatory criteria in the manner suggested by the guidance and in your attempt to address the issues we have identified. We believe that we have considered the least burdensome approach to resolving the issues presented in the guidance document. If, however, you believe that there is a less burdensome way to address the issues, you should follow the procedures outlined in "The Least Burdensome Provisions: Concept and Principles; Guidance for Industry and Food and Drug Administration Staff."

3. The Content and Format of an Abbreviated 510(k) Submission

An Abbreviated 510(k) submission must include the required elements identified in 21 CFR 807.87, including the proposed labeling for the device sufficient to describe the device, its intended use, and the directions for its use. In an Abbreviated 510(k), FDA may consider the contents of a summary report to be appropriate supporting data within the meaning of 21 CFR 807.87(f) or (g); therefore, we recommend that you include a summary report. The report should describe how this special control guidance document was used during the device development and testing and should briefly describe the methods or tests used and a summary of the test data or description of the acceptance criteria applied to address the risks identified in this guidance document, as well as any additional risks specific to your device. This section suggests information to fulfill some of the requirements of 807.87 as well as some other items that we recommend you include in an Abbreviated 510(k).


The coversheet should prominently identify the submission as an Abbreviated 510(k) and cite the title of this class II special controls guidance document.

Proposed labeling

Proposed labeling should be sufficient to describe the device, its intended use, and the directions for its use. (Refer to Section 7 for specific information that should be included in the labeling for devices of the types covered by this document.)

Summary report

The summary report should contain:

  • Description of the device and its intended use. We recommend that the description include a complete discussion of the performance specifications and, when appropriate, detailed, labeled drawings of the device. You should also submit an "indications for use" enclosure.2
  • Description of device design requirements.
  • Identification of the Risk Analysis method(s) used to assess the risk profile in general as well as the specific device’s design and the results of this analysis. (Refer to Section 5 for the risks to health generally associated with the use of this device that FDA has identified.)
  • Discussion of the device characteristics that address the risks identified in this class II special controls guidance document, as well as any additional risks identified in your risk analysis.
  • A brief description of the test method(s) you have used or intend to use to address each performance aspect identified in Section 6 of this class II special controls guidance document. If you follow a suggested test method, you may cite the method rather than describing it. If you modify a suggested test method, you may cite the method but should provide sufficient information to explain the nature of and reason for the modification. For each test, you may either (1) briefly present the data resulting from the test in clear and concise form, such as a table, or (2) describe the acceptance criteria that you will apply to your test results.3 (See also 21 CFR 820.30, Subpart C - Design Controls for the Quality System Regulation.)
  • If any part of the device design or testing relies on a recognized standard, (1) a statement that testing will be conducted and meet specified acceptance criteria before the product is marketed, or (2) a declaration of conformity to the standard.4 Please note that testing must be completed before submitting a declaration of conformity to a recognized standard. (21 USC 514(c)(2)(B)). For more information refer to the FDA guidance, Appropriate Use of Voluntary Consensus Standards in Premarket Submissions for Medical Devices; Guidance for Industry and Food and Drug Administration Staff.

If it is not clear how you have addressed the risks identified by FDA or additional risks identified through your risk analysis, we may request additional information about aspects of the device’s performance characteristics. We may also request additional information if we need it to assess the adequacy of your acceptance criteria. (Under 21 CFR 807.87(l), we may request any additional information that is necessary to reach a determination regarding substantial equivalence.)

As an alternative to submitting an Abbreviated 510(k), you can submit a Traditional 510(k) that provides all of the information and data required under 21 CFR 807.87 and described in this guidance. A Traditional 510(k) should include all of your methods, data, acceptance criteria, and conclusions. Manufacturers considering modifications to their own cleared devices should consider submitting Special 510(k)s.

The general discussion above applies to any device subject to a special controls guidance document. The following is a specific discussion of how you should apply this special controls guidance document to a premarket notification for a cyclosporine and tacrolimus assays.

2 Refer to Indications for Use Form (PDF File Size: 1.03MB) for the recommended format. 

3 If FDA makes a substantial equivalence determination based on acceptance criteria, the subject device should be tested and shown to meet these acceptance criteria before being introduced into interstate commerce. If the finished device does not meet the acceptance criteria and, thus, differs from the device described in the cleared 510(k), FDA recommends that submitters apply the same criteria used to assess modifications to legally marketed devices (21 CFR 807.81(a)(3)) to determine whether marketing of the finished device requires clearance of a new 510(k).

4 See Required Elements for a Declaration of Conformity to a Recognized Standard (Screening Checklist for All Premarket Notification [510(K)] Submissions).

4. Scope

The scope of this guidance is limited to the following devices:

FDA identifies the generic cyclosporine assays classified under 21 CFR 862.1235 and generic tacrolimus assays classified under 21 CFR 862.1678. The product codes are:

  • MKW Cyclosporine
  • MAR Cyclosporine And Metabolites Serum Assay
  • LTB Cyclosporine Radioimmunoassay
  • MGU Fluorescence Polorization Immunoassay For Cyclosporine
  • MGS High Performance Liquid Chromatography For Cyclosporine
  • MGV Radioimmunoassay For Cyclosporine
  • MLM Enzyme Immunoassay, Tacrolimus

This generic type of device includes immunoassays and chromatographic assays for cyclosporine and tacrolimus.

5. Risks to Health

There are no known direct risks to patient health. However, failure of the test to perform as indicated or error in interpretation of results may lead to improper patient management. A falsely low cyclosporine or tacrolimus measurement could contribute to a decision to raise the dose above that which is necessary for therapeutic benefit. This could result in increased risk of toxicity from an elevated drug level. A falsely high cyclosporine or tacrolimus measurement could contribute to a decision to decrease the dose below that which is necessary for immunosuppression. This could result in increased risk of rejection of the transplanted organ. Moreover, no firm therapeutic range exists for cyclosporine or tacrolimus [1-3]. Optimal ranges for patients depend upon many factors such as transplant type, sensitivity of patient, co-administered drugs, and time post-transplant as well as metabolite cross-reactivity of the specific commercial assay used. Therefore, use of assay results to adjust a treatment regimen without consideration of other clinical factors could pose a risk.

In the table below, FDA has identified the risks to health generally associated with the use of the cyclosporine and tacrolimus assays addressed in this document. The measures recommended to mitigate these identified risks are given in this guidance document, as shown in the table below. You should also conduct a risk analysis, prior to submitting your premarket notification , to identify any other risks specific to your device. The premarket notification should describe the risk analysis method. If you elect to use an alternative approach to address a particular risk identified in this guidance document, or have identified risks additional to those in the guidance, you should provide sufficient detail to support the approach you have used to address that risk.

Identified risk

Recommended mitigation measures

improper patient management

Sections 6 and 7

6. Performance Characteristics

General Study Recommendations

Whenever possible, you should include patient samples or sample pools, derived from the intended use population (i.e., patients taking cyclosporine or tacrolimus) for the analytical protocols described below. Minimally, samples from patients taking cyclosporine or tacrolimus should be included in the precision and recovery studies. This is important because patient samples reflect the relevant proportions of free and bound drug, metabolites, and other drugs commonly co-administered to transplant patients and therefore help demonstrate robustness of the assay.

Although spiked samples can be used to supplement the studies, FDA cautions against using spiked samples as the only matrix in the evaluations, because spiked samples may not provide an accurate assessment of the performance characteristics. FDA recommends that you do not use hemolysates (often found in control or calibrator material) in the analytical studies, because these specimens may not test the effects of all preparatory steps on test performance.

You should perform all of your analytical protocols in accordance with the procedures you recommend to users in the package insert, in order to reflect performance expected by the user. Therefore, ensure that all steps (e.g., cell lysis, extraction, centrifugation) are included in each of the analytical studies and that all manufacturer recommended quality control and calibration procedures are followed.

So that acceptance criteria or data summaries can be best interpreted during review, you should provide appropriate specifics concerning protocols. These specifics are also necessary to aid users in interpreting information in your labeling. For example, when referring to NCCLS evaluation protocols or guidelines, you should indicate which specific aspects of the protocols or guidelines you followed.

In studies using spiked samples, you should provide information about purity of drugs, metabolites, or potential interferents used, as well as the type of sample that drug is spiked into.

Whole blood is the matrix recommended in consensus statements from major scientific groups associated with organ transplantation [1-4]. For assays intended for use in other matrices, FDA believes you need to demonstrate a strong correlation with the analyte in whole blood using specimens from patients on drug therapy. Before initiating a study of this type, you should contact DCLD to discuss your protocol.

Studies typically expected for current cyclosporine and tacrolimus instrument-based assays used in central clinical laboratories are described below. Depending on indications for use, assay methodology, and test performance compared to currently marketed devices, additional studies, including clinical studies, may be appropriate.

Specific Performance Characteristics

You should assess the following performance characteristics, in order to document performance and properly label your device in conformance with 21 CFR 809.10(b)(12). In an Abbreviated 510(k), you may briefly present the data resulting from each test in tabular form5 or (2) describe the acceptance criteria to be applied to the test results. In a traditional 510(k), you should present the data for each of these performance characteristics.


You should characterize within-run, and total precision according to guidelines provided in "Evaluation of Precision Performance of Clinical Chemistry Devices;" Approved Guideline (1999) National Committee for Clinical Laboratory Standards (NCCLS), Document EP5-A. That document includes guidelines for experimental design, computations, and format for statement of claims.

You should evaluate precision for at least three concentrations spanning most of the assay range. Typically these concentrations are chosen to represent (a) sub-therapeutic range or near low end of the reportable range (b) concentrations considered to be within therapeutic range and (c) near high end of reportable range or toxic range. Examples of typical cyclosporine levels tested are near 70 ng/ml, 200 ng/ml and 400 ng/ml. If the assay range extends to considerably higher concentrations, the precision evaluation, including validation with samples from patients taking cyclosporine or tacrolimus, should include higher drug concentrations in order to span the assay range.

You should include precision validation using samples from patients taking cyclosporine or tacrolimus, in order to demonstrate robustness of the assay. If it is not feasible to conduct the entire precision evaluation using such samples then the precision evaluation of patient samples can be supplemented with spiked whole blood samples or pools. However, you should ensure that evaluation of sub-therapeutic level samples are included in the patient sample validation. In most cases6 FDA does not recommend use of hemolyzed controls or samples for precision studies since these specimens may not test the effects of all preparatory steps (e.g., hemolysis steps) on test performance.

The description of your protocol and summary data or acceptance criteria in the summary report should include the items listed below:

  • sample types (e.g., pooled patient samples, spiked whole blood)
  • point estimates of the concentration
  • standard deviations of within-run and total precision
  • sites at which precision protocol was run
  • number of days, runs, and observations.

You should also identify which factors (e.g., instrument calibration, reagent lots, operators) were held constant and which were varied during the evaluation. You should describe the computational methods, if they are different from that described in NCCLS EP5-A.

5 unless a Class II Special Controls Guidance Document recommends scatterplots or other graphical representations.

6 One exception may be in the case of new instrument applications when a previously cleared test system is applied to a new analyzer in the same family as the original.


As a measure of accuracy, you should characterize the percent recovery of cyclosporine or tacrolimus. Typically, these studies involve spiking known amounts of cyclosporine or tacrolimus into samples that are either negative for these drugs or contain known drug concentrations. You should include spiking into samples from patients taking cyclosporine or tacrolimus, as part of the study. Final concentrations of the spiked samples should span a significant part of the reportable range and include potential medical decision levels.

You should evaluate replicates of each concentration or sample. You should choose the number of replicates so that any clinically significant differences observed will be statistically significant. Description of the study protocol in the summary report should include:

  • sample types and concentrations
  • materials used for spiking
  • number of replicates
  • definition or method of calculating recovery.

When reporting summary data or acceptance criteria in the summary report, you should indicate the range of recoveries for each concentration level evaluated since this approach is more informative than describing only average recoveries at each concentration level.


You should characterize the linear range of the assay by evaluating samples whose concentration levels are known relative to each other. The sample concentrations should be evenly distributed across the reportable range of the assay. The appropriate number of replicates and concentration levels depends on the reportable range of the assay. For tacrolimus assays, you should include a minimum of four replicates at five concentration levels. For cyclosporine assays, which typically span wider concentration ranges, you should evaluate additional concentration levels (for example, levels in increments of 50 ng/ml). Diluted patient sample pools are appropriate samples for the study. Evaluation of the Linearity of Quantitative Analytical Methods, Proposed Guideline NCCLS Document EP6-P describes a protocol for sample preparation and value assignment as well as a format for statement of claims. You should evaluate the goodness of fit of the linear model using chi-square or ANOVA, as appropriate.

Some immunoassays may exhibit a "high dose hook effect", in which there is a fall in response of the assay at high concentrations. Whenever appropriate (e.g.,for two-site or sandwich immunoassays), you should extend linearity studies beyond the reportable range to the highest concentrations that may be encountered in clinical settings in order to evaluate whether your device exhibits a high dose hook effect.

The description of your protocol in the summary report should include sample types and preparation, concentrations and number of replicates. The acceptance criteria or summary data should include slope, intercept and confidence intervals of the estimated line, the range of linearity and the degree of deviations (biases) from the estimated line that were observed or that are considered acceptable for various concentration levels. Often these deviations can be best described by listing observed or acceptable values relative to expected values for each level evaluated. FDA recommends this approach. You should include summary data or acceptance criteria for high dose hook effect if it applies to your assay methodology.

You should provide information on how samples outside the reportable range should be treated. If you recommend that users dilute samples that are above the reportable range, you should provide a specific protocol for dilution and include in the summary report a validation of that protocol. You should also clarify how samples with concentrations outside the range of linearity are reported to the user.


In addition to the lower limit of detection, you should characterize the functional sensitivity of the assay, which is the lowest drug concentration for which acceptable assay precision is observed. Often this is considered the concentration at which the inter-assay coefficient of variation is not greater than 20%. As an alternative to determining the functional sensitivity, you can include precision of samples at the lower end of your claimed reportable range in the precision evaluation. (See precision section above.)

The description in the summary report should include sample type, definition of your measures of sensitivity and acceptance criteria or data summary. Clarify in the summary report how measurements below the level of sensitivity are reported to the user.

Specificity for parent compound

As a measure of assay specificity, you should characterize cross-reactivity with cyclosporine or tacrolimus metabolites. Metabolites that should be included for cyclosporine specificity studies are AM1, AM4n, AM9, AM19, AM1c, AM1c9 (see reference 7, figure 2 for definitions). Metabolites that should be included for tacrolimus specificity studies are MI, MII, MIII, MIV, MV, MVI, MVII, MVIII (see reference 2, table 3 for definitions). Typically, these studies involve spiking the metabolites into drug-free whole blood pools to final concentrations of at least 1000 ng/ml for cyclosporine or 40 ng/ml for tacrolimus. You should evaluate replicates of spiked samples. Materials of high purity should be used for these protocols, whenever available. You should describe the purity of metabolites used.

The description of your protocol and data summary or acceptance criteria in the summary report should include description of types of samples used for spiking, number of replicates, concentration of metabolite, computation or definition of cross-reactivity used and percent cross-reactivity for each metabolite.


You should characterize the effects of potential interferents on assay performance. Potential sources of interference that you should test include the following:

(1) endogenous compounds, such as (where applicable, the recommended upper limit concentration is given in parentheses):

  • bilirubin (60 mg/dL)
  • triglycerides (1500 mg/dL)
  • cholesterol (500 mg/dL)
  • uric acid (20 mg/dL)
  • rheumatoid factor (500 IU/ml)
  • hematocrit (15-60%)
  • albumin (12g/dL)
  • gamma globulin (12g/dL)
  • human anti-mouse antibodies, HAMA 

(2) commonly co-administered drugs including, but not limited to:

  • cyclosporine
  • tacrolimus
  • mycophenolic acid and its metabolite, MPAG
  • rapamycin
  • common over-the-counter drugs

(3) anticoagulants or preservatives with which the sample is likely to come in contact, such as EDTA. When testing these interferents, you should adjust cyclosporine or tacrolimus concentrations in the sample to near medical decision level or to a known concentration in the middle of the assay range. Typically, interference studies involve adding potential interferent to the sample containing the drug and determining any bias in recovery of cyclosporine or tacrolimus, relative to a control sample (to which no interferent has been added). Appropriate experimental designs, including guidelines for selecting interferents for testing, are described in detail in "Interference Testing in Clinical Chemistry; Proposed Guideline" (1986) National Committee for Clinical Laboratory Standards, Document EP7-P, which proposes the following recommendations. 

  • For endogenous substances, test up to the highest concentration expected based on experience with the intended use population. Interference studies using samples naturally high in the endogenous compound being tested can be informative and this approach should be considered when such samples are available.
  • For drug levels, test up to levels 10-fold higher than highest concentration reported following therapeutic dosage.
  • For specimen additives, test up to levels five times the recommended concentration.

If you observe interference at the concentration levels tested, you should test lower levels in order to determine the lowest concentration that could cause interference. You should test replicate samples in these protocols.

The description of your protocol and acceptance criteria in the summary report should include the following items: 

  • types and levels of interferents tested
  • sample type (e.g., spiked whole blood pools, samples naturally high in endogenous compounds)
  • concentrations of cyclosporine or tacrolimus in the sample
  • number of replicates tested
  • definition or method of computing interference.

When reporting acceptance criteria or data summary in the summary report, you should identify any observed trends in bias (i.e., negative or positive) and indicate the range of observed recoveries in the presence of the particular interferent. This approach is more informative than listing average recoveries alone.

For substances listed as non-interfering, you should state the criteria on which this is based, e.g., inaccuracies due to these substances are less than x % at cyclosporine concentrations of 200 ng/ml. If any potential interferents are known from the literature or other sources to interfere with the test system, you should include them in the labeling. You may not need to perform any additional interference testing with these known interferents.

Specimen collection and handling conditions

You should substantiate the labeled recommendations for specimen storage and transport, by assessing whether the device can maintain acceptable performance (e.g., precision, accuracy) over the storage times and temperatures (including freeze/thaw cycles) recommended to users. An appropriate study includes analysis of sample aliquots stored under the conditions of time, temperature, or allowed number of freeze/thaw cycles recommended in the package insert. You should state the criteria in the summary report for acceptable range of recoveries under the recommended storage and handling conditions.

Method comparison

Currently marketed cyclosporine and tacrolimus assays vary significantly in terms of cross-reactivity patterns with metabolites whose therapeutic and toxic effects are not well-defined [9-13]. Therefore, you should compare the new assay to a candidate reference method, specific for the parent compound. Carefully validated high performance liquid chromatography methods that measure parent drug specifically, such as methods described in references [14-16], should be used as reference procedures. In addition, for immunoassays, it may be beneficial to conduct a comparison study to a predicate device using an immunoassay technology similar to the new device.

You should follow the guidelines provided in the document, Method Comparison and Bias Estimation Using Patient Samples; Approved Guideline (1995) National Committee for Clinical Laboratory Standards, Document EP9A concerning experimental guidelines and statement of claims. You should evaluate patient samples with drug concentrations distributed across the reportable range of the assay. Cyclosporine is currently indicated for heart, liver and kidney transplant patients. Tacrolimus is indicated for kidney and liver tranplant patients. Since variations in assay performance have been observed for the various organ transplant types [9-11], you should evaluate samples from patients with heart, liver and kidney transplants for cyclosporine test systems and samples from liver and kidney transplant patients for tacrolimus test systems. Banked (retrospective) samples are appropriate for these studies as long as the information listed below concerning sample characterization is available. FDA believes it is helpful for samples from patients undergoing various treatment regimens to be included, and therefore recommends including samples from multiple geographic sites or clinical centers.

Appropriate sample size depends on factors such as precision, interference, range, and other performance characteristics of the test. The number of patients should also be large enough so that inter-individual variation would be observed. A statistical justification to support the study sample size should be provided in the protocol description in the summary report. We expect that the sample size target, however supported, will include a minimum of 50 samples from 50 individual patients for each organ transplant group, for which the drug and test are indicated (i.e., a minimum of 100-150 samples total).

If, in addition to samples discussed above, you choose to include multiple measurements from individual patients, you should summarize your results of appropriate statistical analyses such as Analysis of Variance, Generalized Estimating Equations, or Bootstrapping, to account for correlation of repeat measurements within patients in the study. If you choose to include multiple measurements from individuals you should ensure that they range over time, post-transplant.

For your data summary or acceptance criteria to be properly interpreted during the review process you should provide all relevant information on the sample population in the summary report and the package insert.

Information on sample population should include the number of:

  • individual patients represented by the samples;
  • data points;
  • clinical sites; and
  • samples from each transplant type.

You should state any specific selection criteria for samples. You should also indicate whether samples were collected from patients with specific clinical outcomes, or from centers using atypical or novel drug regimens. Factors such as age range (e.g., adults), time post-transplant (e.g., chronic, acute), and time of blood draw with respect to drug administration (e.g., trough, 2 hour) can influence drug-to-metabolite ratios and consequently, assay bias [17,18]. Therefore, you should describe these features of the sample population. You should clarify in the summary report the HPLC method used, and include references to validation of the procedure from the literature.

You should conduct separate analyses of data for each organ transplant group for which the test is indicated. If samples evaluated in the study include both trough and other times of blood draw relative to drug administration7, you should conduct separate analyses for these groups as well. When providing the results of the method comparison study, you should include the following information:

  • Scatterplots of the new assay versus the reference (e.g., HPLC) method. The plots should contain all data points, the estimated regression line and the line of identity. Data points in the plot should represent individual measurements.
  • A description of the method used to fit the regression line and results of regression analysis including the slope and intercept with their 95% confidence limits, the standard error of the estimate (calculated in the y direction), and correlation coefficient should be included in the summary report. In cases where parameters are not consistent throughout the reportable range, estimates of more than a single range may be appropriate. If the comparator, as well as the new assay is subject to measurement error, a regression method such as the Deming method may be appropriate, rather than Least Squares [19].
  • To illustrate the degree of inter-individual variations, you should include graphs of difference in measurements (i.e., new device minus reference HPLC method) versus the reference HPLC method. Appropriate representations include a bias plot of difference in measurements (y - x) versus the reference method (x), as recommended in NCCLS EP9 [20], or versus the mean of y and x, as recommended by Bland and Altman [21].

In the 510(k) summary report, you should explain how the summary data or acceptance criteria for the method comparison study support substantial equivalence. If you are submitting a traditional 510(k), you may also choose to include line data in order to clarify your protocol or results.

7 FDA currently considers the evaluation of trough samples sufficient for method comparison, as long as these samples sufficiently span the claimed therapeutic range.

Studies at external sites

You should demonstrate substantial equivalence at external laboratory sites in addition to that of the manufacturer. FDA recommends that you evaluate the assay in at least two sites. You may choose to include this as part of the method comparison study described above. Data from individual sites should initially be analyzed separately to evaluate any inter-site variation and results of the analysis should be included in the 510(k) summary report. Method comparison results from the individual sites can be pooled in the package insert, if you demonstrate that there are no significant differences in results among sites.


You should provide the following information about the calibrators in the assay kit in your summary report:

  • Protocol and acceptance criteria for real-time or accelerated stability studies for opened and unopened calibrators.
  • Protocol and acceptance criteria for value assignment and validation, including any specific instrument applications or statistical analyses used.
  • Identification of traceability to a domestic or international standard reference material.
  • Protocol and acceptance criteria for the transfer of performance of a primary calibrator to a secondary calibrator.

For information about calibrators marketed separately as class II devices under 862.1150, see the guidance "Abbreviated 510k Submissions for In Vitro Diagnostic Calibrators" (Withdrawn).

7. Labeling

The premarket notification should include labeling in sufficient detail to satisfy the requirements of 21 CFR 807.87(e). The following suggestions are aimed at assisting you in preparing labeling that satisfies the requirements of 21 CFR 807.87(e)8

8 Although final labeling is not required for 510(k) clearance, final labeling must also comply with the requirements of 21 CFR 801 or 21 CFR 809.10 before a medical device is introduced into interstate commerce. In addition, final labeling for prescription medical devices must comply with 21 CFR 801.109. Labeling recommendations in this guidance are consistent with the requirements of part 801 and section 809.10.


You should discuss the importance of consistency of time of blood draw with respect to last dose, as well as time of day. Consistency of time of day may be important considering reports that Cyclosporine A concentrations display a circadian rhythm with evening trough levels being significantly lower than morning trough levels [22].

You should discuss any limitations or instructions related to the specimen, such as appropriate matrices or anticoagulants (in most cases, EDTA).

You should provide instructions concerning preserving integrity of the specimen, such as temperatures for collection, transport, storage (short and long term) and procedural steps of the assay necessary to maintain assay performance. Storage conditions recommended to the user should be based on the conditions you have validated for your test system. You should clearly define any acceptance criteria that you apply in determining the recommended storage conditions (e.g., inaccuracies due to instability under these conditions are less than 10% for 95% of samples tested). Additional information on storage conditions based on literature can be cited if they are applicable to your test system.

Assay procedure

You should include appropriate time limits and temperature requirements for the procedural steps. Whenever applicable, you should describe expected appearance of the specimen through various procedural steps and advise users of any signs that may indicate whether the assay is proceeding correctly.

You should advise users how to proceed for samples with concentrations above the highest calibrator. If you instruct users to dilute these samples, you should provide a validated procedure for the dilution.

You should advise users of any steps that can be taken to minimize effect of carryover, or other causes of bias or irreproducibility, based on procedures you have validated for your test system.

Quality control

You should advise users of the specifics of calibration and quality control procedures necessary to ensure the performance claims of the system and include instructions for interpretation of the results of quality control samples, satisfactory limits of performance and instructions on how to proceed if limits of performance are not satisfied. You should include recommendations for appropriate quality control specimens. Consensus documents recommend that whole blood assays should employ whole blood controls with well-characterized drug preparations [4].


You should include the following limitation, when appropriate for your device type.

Patients with abnormal liver function, elevated bilirubin levels, unexpectedly high drug values, or increased time post-therapy may have impaired drug elimination and metabolite accumulation. For such patients, use of this assay may be supported with a method more specific for the parent compound (e.g., HPLC).

You should identify any exogenous or endogenous factors known to affect results and describe the effect on results (e.g., highly lipemic samples may cause falsely low results).

A number of drug interactions with cyclosporine and tacrolimus are mediated at the metabolic level. References listing drugs currently known to interact with metabolism of cyclosporine and tacrolimus should be cited in an appropriate section of the package insert.

Therapeutic ranges

Since therapeutic ranges vary depending on the methodology used as well as the clinical state of the individual, stating one specific therapeutic range is usually not appropriate for current cyclosporine and tacrolimus assays.

You should include cautionary explanations concerning the lack of firm therapeutic ranges to the user. You should discuss both patient variability and test variability. For example:

No firm therapeutic range exists for cyclosporine [tacrolimus] in whole blood. The complexity of the clinical state, individual differences in sensitivity to immunosuppressive and nephrotoxic effects of cyclosporine, co-administration of other immunosuppressants, type of transplant, time post-transplant and a number of other factors contribute to different requirements for optimal blood levels of cyclosporine. Therefore, individual cyclosporine values cannot be used as the sole indicator for making changes in treatment regimen and each patient should be thoroughly evaluated clinically before changes in treatment regimens are made. Each user must establish his or her own ranges based on clinical experience.

Therapeutic ranges vary according to the commercial test used, and therefore should be established for each commercial test. Values obtained with different assay methods cannot be used interchangeably due to differences in assay methods and cross-reactivity with metabolites, nor should correction factors be applied. Therefore, consistent use of one assay for individual patients is recommended.

Performance Characteristics

You should describe the protocol and results for each performance characteristic discussed in Section 6. Protocol descriptions and results in the package insert should include all of the information cited in Section 6, including scatterplots of the new assay versus the reference (e.g., HPLC) method and, in some cases, graphs of inter-individual variation or equivalent information, in order to best represent results of the method comparison for the user. See also applicable sections in the NCCLS guidelines cited in Section 6 concerning statements of claims.

8. New Instrument Applications

For information concerning application of cleared or approved test systems to additional analyzers, see the guidance entitled "Replacement Reagent and Instrument Family Policy". The approach described in that guidance is appropriate in cases when performance characteristics on the new analyzer meet pre-determined acceptance criteria specified in a protocol submitted by the manufacturer and reviewed by the FDA. If performance characteristics do not meet pre-determined acceptance criteria, a new 510(k) (which may be an Abbreviated 510(k)) is appropriate.

When the new analyzer is within the same family and does not involve any changes in reagents, sample treatment, or assay procedure that could potentially affect cross-reactivity or partitioning of metabolites, it is sufficient for the method comparison studies in the protocol to include comparison of samples on the new instrument to the previously cleared instrument. In this case, results of the method comparison study of the original test system versus the HPLC reference procedure should still be available to the user in the package insert. In contrast, when application to a new analyzer does include changes in reagents, sample treatment or procedure, a method comparison study including HPLC should be included in the protocol for the add-to and results should be included in the labeling.

9. References

1.Oellerich, M, Armstrong, VW, Kahan, B, Shaw L, Holt, DW, Yatscoff, R, Lindholm, A, Halloran, P, Gallicano, K, Wonigeit, K, Schutz, E, Schran, H, Annesley, T, Lake Louise Consensus Conference on Cyclosporine Monitoring in Organ Transplantation: Report of the consensus panel, Therapeutic Drug Monitoring 1995;17:642-654.

2.Jusko, WJ, Thomson, AW, Fung, J, McMAster P, Wong, SH, Zylber-Katz E, Christians, U, Winkler M, Fitzsimmons, WE, Lieberman R, McBride J, Kobayashi M, Warty V, Soldin SJ, Consensus Document: Therapeutic monitoring of tacrolimus (FK-506), Therapeutic Drug Monitoring 1995;17:606-614.

3.Oellerich M, Armstrong VW, Schutz, E, Shaw LM, Therapeutic monitoring of cyclosporine and tacrolimus, Clinical Biochemistry 1998;31:309-316.

4.Shaw, LM, Yatscoff RW, Bowers LD, Freeman DJ, Jeffrey JR, Keown PA McGilveray IJ, Rosano TG, Wong PY, Canadian Consensus Meeting on Cyclosporine Monitoring: Report of the Consensus Panel, Clinical Chemistry 1990;36:10.

5. Evaluation of Precision Performance of Clinical Chemistry Devices; Approved Guideline (1999) National Committee for Clinical Laboratory Standards, Document EP5-A

6. Evaluation of the Linearity of Quantitative Analytical Methods; Proposed Guideline National Committee for Clinical Laboratory Standards, Document EP6-P.

7. Holt, DW, Johnston A, Roberts NB, Tredger JM, Trull, AK, Methodological and Clinical Aspects of cyclosporine monitoring: Report of the Association of Clinical Biochemists Task Force, Ann Clin Biochem 1994; 31: 420-426.

8. Interference Testing in Clinical Chemistry; Proposed Guideline (1986) National Committee for Clinical Laboratory Standards, Document EP7-P.

9. Steimer, W, Performance and specificity of monoclonal immunoassays for cyclosporine monitoring: How specific is specific? Clinical Chemistry 1999;45:371-381.

10. Schutz D., Svinarov D, Shipkova M, Niedmann P, Armstrong VW, Wieland E, Oellerich M, Cyclosporine with Whole Blood Immunoassays (AxSym, CEDIA and EMIT) A critical overview of performance characteristics and comparison with      HPLC, Clinical Chemistry 1998; 44:2158-2164.

11. Holt DW, Johnston A, Kahan BD, Morris RG, Oellerich M, Shaw M, New approaches to Cyclosporine monitoring raise further concerns about analytical techniques, Clinical Chemistry 2000;46:872.

12. Murthy JN, Davis DL, Yatscoff RW, Soldin SJ, Tacrolimus metabolite cross-reactivity in different Tacrolimus assays, Clinical Biochemistry 1998;31:613-617.

13. Cao Z, Linder MW, Jevans AW, Brown G, Valdes Jr R, Comparison of Tacrolimus concentrations measured by the Imx Tacrolimus vs the PROTRAC II FK506 ELISA assays, Clinical Chemistry 1999;45:1868-1870.

14. Volosov A, Napoli KL, Soldin SJ, Simultaneous simple and fast quantification of three major immunosuppressants by liquid chromatography tandem mass spectrometry, Clinical Biochemistry 2001;34:285-290.

15. Zhang Q, Simpson J, Aboleneen HI, A specific method for the measurement of tacrolimus in human whole blood by liquid chromatography/tandem mass spectrometry, Therapeutic Drug Monitoring 1997;19:470-476.

16. Taylor PJ, Hogan NS, Lynch SV, Johnson AG, Pond SM., Improved therapeutic drug monitoring of Tacrolimus (FK506) by tandem mass spectrometry, Clinical Chemistry 1997;43:2189-2190.

17. Hamwi A, Salomon A, Steinbrugger R, Fritzker Sekeres M, Jager W, Szekeres T, Cyclosporine Metabolism in patients after kidney bone marrow, heart-lung and liver transplantation in the early and late posttransplant periods, American Journal of Clinical Pathology 2000;114:536-543.

18. Fernandez-Marmiesse A, Hermida J, Tutor C, Comparison of predose versus 2-hour postdose blood metabolites/cyclosporine ratios in kidney and liver transplant patients, Clinical Biochemistry 2000;33:383-386.

19. Linnet, K, Evaluation of regression procedures for method comparison studies, The Lancet 1993;39:424-432.

20. Method Comparison and Bias Estimation Using Patient Samples; Approved Guideline (1995) National Committee for Clinical Laboratory Standards, Document EP9-A.

21. Bland JM, Altman DG, Comparing methods of measurement: Why plotting difference against standard method is misleading, Lancet 1995;346:1085-1087.

22. Choi JS, Park HJ, Circadian changes in pharmacokinetics of cyclosporine in healthy volunteers, Research Communications in Molecular Pathology and Pharmacology 1999; 103:109-112.

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