On December 23, 2016, the FDA alerted 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 IgM Capture ELISA test.
The ZIKV Detect test is used for the preliminary (presumptive) detection of Zika virus IgM antibodies in human sera collected from patients who meet the CDC Zika virus clinical criteria—patients with a history of clinical signs and symptoms associated with Zika virus infection—and/or epidemiological criteria—patients with a history of residence in or travel to a geographic region with active Zika transmission at the time of travel.
Because confirmation tests may take a week to a month to complete, the FDA issued this alert to ensure that health care providers and patients know about a higher likelihood of false positive results. The ZIKV Detect test, while useful in ruling out Zika exposure, requires confirmatory testing.
In August 2016, the FDA authorized the ZIKV Detect IgM Capture ELISA manufactured by InBios International, Inc., as the first commercially available Zika serological IgM test. Subsequently, several commercial laboratories began migrating their serological testing from the CDC assay authorized at the beginning of 2016 to the ZIKV Detect IgM Capture ELISA.
The CDC test and the ZIKV Detect test report only presumptive positive results. Samples must 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.
As of December 23, 2016, the FDA had not yet determined if the reported false positives were related to the ZIKV Detect test or the commercial testing facility.
The FDA urged health care providers to be aware of two characteristics of Zika testing. First, 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 the CDC or by qualified laboratories. Second, the confirmatory testing may take a week to a month to be performed, but can be prioritized if the CDC is aware that the sample is from a pregnant woman. Laboratories should be notified of the patient’s pregnancy status.
The FDA urged healthcare providers for pregnant women meeting CDC Zika virus clinical criteria and/or CDC Zika virus epidemiological criteria to take three actions. First, inform patients that presumptive positive results need to be confirmed, so that pregnant women are not making health care decisions based on incomplete information. Second, do not rely on presumptive positive Zika virus IgM test results as the sole basis of significant patient management decisions. Doctors are advised to 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. Third, notify the laboratory of the patient’s pregnancy to facilitate prioritization of confirmatory testing by the CDC or qualified laboratories.
See the FDA Safety Alert
See also the CDC’s Clinical Guidance for Healthcare Providers Caring for Pregnant Women
See also the CDC’s Clinical Guidance for Healthcare Providers Caring for Infants & Children
See also the CDC’s Information on Zika and Pregnancy
See also the CDC’s Information on Zika and Women Trying to Become Pregnant
See also Medical Law Perspectives, May 2016 Report: Vectors of Risk: Zika, West Nile, and Similar Tick and Mosquito Disease Litigation
See also Medical Law Perspectives, March 2014 Report: Blood Draws, Testing, Transfusions: Venipuncture Injury, Inaccurate Results, Tainted Blood - The Liability Risks