Laboratory Testing

IMPORTANT NOTICE: Updated Zika Testing Guidance

On April 2, 2018, DSHS updated its testing guidance for pregnant women in Texas.

  • Pregnant women who live in Cameron, Hidalgo, Kinney, Maverick, Starr, Val Verde, Webb, Willacy, and Zapata counties should be tested three times during pregnancy using PCR only.
  • Elsewhere in the state, pregnant women with no symptoms but recent possible exposure (for example, women who have traveled to areas with ongoing Zika transmission) should be tested as soon as possible, up to 12 weeks after exposure, using PCR only.
  • DSHS recommends that Zika virus PCR testing be performed on paired urine and serum specimens when possible. Doing so maximizes the sensitivity of the testing, since persistence of viral RNA in various body fluids is not uniform. Serum specimens can be tested without a paired urine specimen, but urine specimens cannot be tested without a paired serum specimen.

The guidance for testing non-pregnant residents remains the same.

  • Residents of the nine higher-risk counties with a rash plus one other common Zika symptom (fever, joint pain or conjunctivitis) should be tested.
  • Residents of any part of the state with three or more Zika symptoms should be tested.
  • Any non-pregnant resident with Zika symptoms starting within two weeks of travel to an area with ongoing Zika transmission or sexual contact with a potentially exposed traveler should be tested.

Read the DSHS Health Alert for more information. Visit the Health Professionals page of this website for information about caring for pregnant women and patients exposed to Zika.

The DSHS Austin Laboratory and many other Texas Laboratory Response Networks (LRNs) are performing the Trioplex Real-Time reverse transcriptase polymerase chain reaction (rRT-PCR) for Zika and the Zika virus-specific IgM Antibody Capture Enzyme-Linked Immunosorbent Assay (Zika MAC-ELISA). Please review the Chikungunya, Dengue, and Zika PCR and Serology Specimen Criteria guidance document (75 kb, PDF) (updated Dec. 16, 2016) to facilitate laboratory testing of individuals meeting the testing criteria. Specimens submitted to the DSHS Austin Laboratory must be accompanied by a G2-V form and a completed Chikungunya, Dengue, and Zika Testing Supplemental Information Form (65 kb, PDF) (updated Sept. 12, 2016). The plaque-reduction neutralization test (PRNT), used to confirm Zika virus infection, is available at the U.S. Centers for Disease Control and Prevention (CDC) and some state laboratories.

On May 31, 2017 the CDC released interim guidance on Zika virus antibody testing and interpretation of results. Because of the differences in recommended clinical management of Zika and dengue virus infections, and the risk of adverse pregnancy outcomes in women infected with Zika virus during pregnancy, a conservative approach to the interpretation of antibody test results is necessary to reduce the possibility of a missed diagnosis of either infection. The timing of IgM antibody testing and the thresholds of plaque reduction neutralization test (PRNT) have changed.

  • For symptomatic pregnant women, both the IgM test and real-time reverse transcription polymerase chain reaction (rRT-PCR) test should be performed concurrently, as soon as possible or up to 12 weeks after symptoms began; if the RT-PCR result is negative, and the Zika IgM test result is non-negative, then PRNT should be performed.
  • Based on earlier flavivirus research and limited preliminary data specific to Zika virus, the historical use of a 4-fold higher titer by PRNT might not discriminate between anti-Zika virus antibodies and cross-reacting antibodies in persons who have been previously infected with or vaccinated against a related flavivirus (i.e., secondary flavivirus infection).
  • Together with a positive or equivocal IgM to Zika or dengue virus:
    • A PRNT titer >10 will be interpreted as a evidence of infection with that specific flavivirus infection when the PRNT to the other flavivirus(es) tested is <10.
    • A PRNT titer <10 to a specific flavivirus will be interpreted as no evidence of infection with that virus.
    • If PRNTs are positive i.e., >10 to multiple flaviviruses, this will be interpreted as evidence of recent infection with a flavivirus.

CDC will continue to update this guidance as additional data becomes available. For more information about this guidance, visit Interim Guidance for Interpretation of Zika Virus Antibody Test Results .

Additional guidelines for healthcare providers are on the Health Professionals page.

If you are unsure whether your patient meets the recommended testing criteria for DSHS, please contact your local health department or DSHS public health region for assistance.