Zika MAC-ELISA: Key Facts

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The page below is a sample from the LabCE course Zika Virus: Overview and Laboratory Testing. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Zika MAC-ELISA: Key Facts

  • If the positive control P/N is ≥ 2.0, then the testing is valid, and the results can be released.
  • If the P/N result for the patient specimen is <2, the test is considered negative and reported as, "no evidence of recent Zika virus infection detected." Typically, no further analysis is required.
  • If the patient's P/N result is between 2 and 3, the test is considered equivocal and is reported as, "equivocal for anti-Zika virus antibodies."
  • If the patient's P/N result is ≥ 3.0, then the test is considered presumptive positive and is reported as, "serological evidence of possible Zika virus infection. Additional testing is required."
  • Important note: Zika IgM levels over the course of illness are not well characterized. IgM levels are variable, but generally, levels are positive starting near day four post onset of symptoms and continuing for 12 or more weeks following initial infection.
  • The results of this test cannot be used as the sole basis of patient management decisions and must be combined with clinical observations, patient history, epidemiological information, and other laboratory evidence.
  • Negative results do not preclude the possibility of Zika virus infection, past or present. Negative results may be seen in specimens collected before day four post onset of symptoms or after the window of detectable IgM closes.
  • It is equally important to understand that cross-reaction with other flaviviruses and possible nonspecific reactivity can occur, making results difficult to interpret. Consequently, presumed positive, equivocal, or inconclusive tests must be forwarded for confirmation by plaque-reduction neutralization testing (PRNT). PRNT is performed by the CDC or a CDC-designated confirmatory testing laboratory to confirm presumed positive, equivocal, or inconclusive IgM results. (Additional description of the PRNT test is in the next section).
The table below is a summary of the interpretation and reporting of the Zika MAC-ELISA test results:
Test Specimen
Zika virus infection not detected.
Report results. If an early acute specimen, refer to interpretation instructions above.
2 P/N < 3
Zika MAC-ELISA results were equivocal for the presence of anti-Zika virus antibodies.
Send report to CDC along with the specimen for confirmatory testing.
≥ 3
Presumptive Positive
Serological evidence of possible recent Zika virus infection identified. Additional testing required.
Send report to CDC along with the specimen for confirmatory testing.