AUDIENCE: OBGYN, Internal Medicine, Infectious Disease, Family Practice
ISSUE: The FDA is alerting physicians who care for pregnant women meeting CDC Zika virus clinical criteria and/or CDC Zika virus epidemiological criteria, that the U.S. commercial testing facility, Laboratory Corporation of America (LabCorp), has reported some false positive results from the ZIKV Detect test.
Because confirmation tests may take a week to a month to complete, the FDA is issuing this alert so that health care providers and patients know about a higher likelihood of false positive results.
While the FDA has not yet determined if the reported false positives are related to the ZIKV Detect test or the commercial testing facility, it is important to remember that IgM tests remain useful in ruling out Zika exposure but require confirmatory testing.
BACKGROUND: The ZIKV Detect IgM Capture ELISA is used for the preliminary (presumptive) detection of Zika virus IgM antibodies in human sera collected from patients with a history of clinical signs and symptoms associated with Zika virus infection (Centers for Disease Control and Prevention [CDC] clinical criteria for Zika virus) and/or a history of residence in or travel to a geographic region with active Zika transmission at the time of travel (CDC Zika virus epidemiological criteria).
In August of this year, the FDA authorized the ZIKV Detect IgM Capture ELISA manufactured by InBios International, Inc. as the first commercially available Zika serological IgM test. Since then, several commercial laboratories have started migrating their serological testing from the CDC assay authorized at the beginning of this year to the new commercial assay.
The CDC test and the ZIKV Detect test report only presumptive positive results, and samples have to be sent for confirmation. Past performance characteristics indicate most of the presumptive positive results from both tests have been ultimately confirmed.
After transitioning to the ZIKV Detect test, LabCorp observed higher than expected false positive results. The CDC confirmed less than half of those presumptive positive results captured by LabCorp through the ZIKV Detect test.
RECOMMENDATIONS: The FDA urges health care providers to be aware that:
- Positive IgM Zika virus results are only presumptive for the detection of antibodies to Zika virus.
- Confirmation of IgM Zika virus presumptive or possible positive results requires additional testing by CDC or by qualified laboratories.
- The confirmatory testing may take a week to a month to be performed, but can be prioritized if CDC is aware that the sample is from a pregnant woman. Laboratories should be notified of the patient’s pregnancy status.
The FDA urges health care providers to:
- Inform their patients that presumptive positive results need to be confirmed, so that pregnant women are not making health care decisions based on incomplete information.
- Not rely on presumptive positive Zika virus IgM test results as the sole basis of significant patient management decisions. Take the following into consideration before diagnosing Zika virus infection in pregnant women:
- clinical observations,
- patient history,
- epidemiological information, and;
- results from other testing such as follow-up confirmatory testing.
- Notify the laboratory of the patient’s pregnancy to facilitate prioritization of confirmatory testing by CDC or qualified laboratories.
Healthcare professionals and patients are encouraged to report adverse events or side effects related to the use of these products to the FDA's MedWatch Safety Information and Adverse Event Reporting Program:
- Complete and submit the report Online: www.fda.gov/MedWatch/report
- Download form or call 1-800-332-1088 to request a reporting form, then complete and return to the address on the pre-addressed form, or submit by fax to 1-800-FDA-0178
- Centers for Disease Control and Prevention General Zika Virus Information
- Centers for Disease Control and Prevention Zika Information for Pregnant Women