What Is the Current Window Period for HIV?

Newer Combination Tests Reducing the Time to Get an Accurate Result

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HIV-1 rapid antibody/antigen combination test. Image courtesy Alere, Inc.

With infectious diseases like HIV, the window period is the time between the moment of infection and when that infection can be accurately be detected by either a saliva or urine test. This period is determined by the sensitivity of available tests, many of which are designed to detect antibodies (proteins produced by the body’s immune system in response to an infection), antigens (agents that trigger the immune response) or both.

It is during the window period that a test can deliver a false negative result if the concentration of antibodies or antigens in the blood are insufficient for reliable detection. Testing prematurely not only places a person at risk of misdiagnosis but potentiates further spread of the disease.

The window period should not be confused with the incubation period, which is defined as the period between exposure to a disease and the appearance of the first symptoms of that disease.

What Is the Window Period for HIV?

Current-generation HIV antibody tests have a window period of roughly 21 to 28 days. By week four, the tests are said to have a sensitivity of 95%, meaning that it will deliver a correct result in 95% of cases. By three months, the sensitivity increases to around 99.9%.

By contrast, HIV antigen tests detect the p24 protein found on the surface of HIV and can generally deliver a correct result in between 13 and 28 days, although sensitivity can be sometimes be lower.

Most recently, fourth-generation, rapid combination tests, which test for both antibodies and antigens, are known reduce the window period to between 12 and 26 days, while offering a sensitivity of between 87.5% and 96%. This new technology is seen to be vital in confirming acute stage infection and is considered the gold standard for HIV testing.

HIV Testing Considerations

While newer technologies are able to detect HIV far faster than ever, it is important to note that the window period can vary from person to person depending on the individual's immune response. It is important, therefore, to always speak with your doctor or clinic to ensure you are testing well outside of the window period.

If using a commercial, over-the counter device like the OraQuick in-home HIV test, it is important to note that, as an antibody test, the manufacturers recommended waiting for 3 months before testing. Furthermore, the OraQuick has a false negative rate of around 7%, meaning that one out of every 12 tests will deliver an incorrect "all clear" result.

If in doubt of a result, contact your nearest clinic to schedule a confidential HIV test. You can find a testing site nearest you by accessing the online locator offered by the U.S. Department of Health and Human Services.

The U.S. Preventive Services Task Force (USPSTF) currently recommends that all persons between the ages of 15 and 65 be screened for HIV as part of a routine doctor visit.

Sources:

Department of Health and Human Services (DHHS). "Guidelines for the Use of Antiretroviral Agents in HIV-1-Infected Adults and Adolescents." Accessed December 22, 2014.

Pilcher, C.; Louie, B.; Facente, S.; et al. "Performance of Rapid Point-of-Care and Laboratory Tests for Acute and Established HIV Infection in San Francisco." PLOS | One. December 12, 2013; DOI: 10.1371/journal.pone.0080629.

Malm, K.; von Sydow, M.; and Andersson, S. "Performance of three automated fourth-generation combined HIV antigen/antibody assays in large-scale screening of blood donors and clinical samples." Transfusion Medicine. 2009: 19(2):78-88.

U.S. Preventive Services Task Force (USPSTF). "Screening for HIV: U.S. Preventive Services Task Force Recommendation Statement." Rockville, Maryland; April 2013; accessed February 7, 2014.

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