What Is the Window Period for HIV Testing?

Newer combination tests are faster and more accurate

A blood sample being held with a row of human samples for analytical testing including blood, urine, chemistry, proteins, anticoagulants and HIV in lab
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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 an HIV test. This period is determined by the sensitivity of a test, many of which are designed to detect antibodies (proteins produced by the 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 is insufficient for detection. Testing prematurely not only places a person at risk of misdiagnosis but cause further spread of the disease by people unaware of their status.

The window period should not be confused with the incubation period which is the time between exposure to a disease and the appearance of the symptoms.

Window Period Continues to Shrink

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

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

Most recently, fourth-generation rapid combination tests, which detect antibodies and antigens, have reduced the window period to between 12 and 26 days while offering a sensitivity of 87.5 percent to 96 percent.

This new testing technology is considered the gold standard for HIV testing and is better able to confirm acute infection, allowing for earlier treatment.

Testing Considerations

While newer combination tests are able to detect HIV faster than ever, the actual window period can vary depending on the person's immune response. It is important, therefore, to avoid coming in too early to test. If in doubt, speak with your doctor or health provider for advice.

This is especially true if using an over-the-counter product like the OraQuick in-home HIV test. As an antibody-based test, you should wait at least three months from the time of exposure before testing yourself, according to the manufacturer.

It is also important to note that the OraQuick in-home test has a false negative rate of around seven percent, meaning that one out of every 12 tests will deliver an incorrect "all clear" sign.

If you're unsure about the accuracy of an in-home test, contact your nearest clinic to schedule a confidential HIV test. You can find a testing site near you by accessing the online locator offered by the U.S. Department of Health and Human Services.

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

According to the Centers for Disease Control and Prevention, around 1.2 million Americans are living with HIV of which an estimated 14 percent remain undiagnosed.

Moreover, persons unaware of their HIV status account for a third of all new infections in the U.S.

Sources:

Centers for Disease Control and Prevention. "Prevalence of Diagnosed and Undiagnosed HIV Infections - United States, 2008 to 2012." MMWR. July 26, 2015; 64(24):657-662.

Department of Health and Human Services. "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. "Screening for HIV: U.S. Preventive Services Task Force Recommendation Statement." Rockville, Maryland; April 2013; accessed February 7, 2014.

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