It depends upon how promptly the calibration laboratory fulfilled its responsibilities during the test process and whether the laboratory ever successfully completed a proficiency test before. FDA will generally view the laboratory as having adequately fulfilled these responsibilities if it contacted NIST at least 60 days in advance of the expiration date to request a proficiency test for mammography calibrations and if it promptly performed its part of the calibration process when requested by NIST. If the laboratory takes these actions and NIST is unable to complete the test before the expiration date, then FDA will generally accept the validity of calibrations performed for 60 days after the expiration date, unless the laboratory is notified during that 60 day period that the test failed. If NIST still has not been able to complete the proficiency test by the end of these extra 60 days, the situation will be reviewed by FDA on a case by case basis to determine if additional time can be granted without unduly jeopardizing the public health. Note that a laboratory that has not completed its first proficiency test cannot be used to calibrate air kerma instruments used to meet the MQSA requirements.