FDA Warns of False Positive Results With Zika Test

Results from ZIKV Detect assay require confirmatory testing

The FDA has alerted physicians who care for pregnant women meeting Centers for Disease Control and Prevention (CDC) Zika virus clinical criteria and/or CDC Zika virus epidemiologic 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 issued the alert so that health care providers and patients know about a higher likelihood of false positive results.

The FDA has not yet determined whether the reported false positives were related to the ZIKV Detect test or to the commercial testing facility. The agency emphasized that while immunoglobulin M (IgM) tests remain useful in ruling out Zika exposure, they require confirmatory testing.

The ZIKV Detect IgM Capture enzyme-linked immunosorbent assay (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 (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 epidemiologic criteria).

In August, the FDA authorized the ZIKV Detect IgM Capture ELISA manufactured by InBios International, Inc., as the first commercially available Zika serologic IgM test. Since then, several commercial laboratories have started migrating their serologic 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 that most of the presumptive positive results from both tests have been ultimately confirmed, the FDA noted.

After transitioning to the ZIKV Detect test, LabCorp observed higher-than-expected false positive results. The CDC confirmed less than half of the presumptive positive results.

The FDA advises health care providers to be aware that:

  • Positive IgM Zika virus results are presumptive only for the detection of antibodies to Zika virus.
  • The confirmation of IgM Zika virus presumptive or possible positive results requires additional testing by the CDC or by qualified laboratories.
  • 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.

Source: FDA; December 23, 2016.