HIV Tests For Screening and Diagnosis
HIV tests are very accurate, but no test can detect the virus immediately after infection. How soon a test can detect infection depends upon different factors, including the type of test being used. There are three types of HIV diagnostic tests: antibody tests, combination or fourth-generation tests, and nucleic acid tests (NATs).
Antibody tests detect the presence of antibodies, proteins that a person’s body makes against HIV, not HIV itself. Most HIV tests, including most rapid tests and home tests, are antibody tests. It can take 3 to 12 weeks for a person’s body to make enough antibodies for an antibody test to detect HIV infection. In general, antibody tests that use blood can detect HIV slightly sooner after infection than tests done with oral fluid.
Combination or fourth-generation tests look for both HIV antibodies and antigens. Antigens are a part of the virus itself and are present during acute HIV infection. It can take 2 to 6 weeks for a person’s body to make enough antigens and antibodies for a combination test to detect HIV. Combination tests are now recommended for testing done in labs and are becoming more common in the United States. There is also a rapid combination test available.
NATs detect HIV the fastest by looking for HIV in the blood. It can take 7 to 28 days for NATs to detect HIV. This test is very expensive and is not routinely used for HIV screening unless the person recently had a high-risk exposure or a possible exposure with early symptoms of HIV infection.
The earliest possible testing window period is using a 4th generation duo test, which is considered by many experts to be conclusive at 28 days.
A third generation test will give you a good indication of your status at 6-8 weeks but a final confirmation test is recommended at 12 weeks to be conclusive.
When in doubt, any HIV expert that actually knows what they're talking about will recommend a confirmatory test at 12 weeks or 90 days post exposure. The six to 12 month post exposure window period has been outdated since 2004. So if you're seeing a doctor that recommends anything past 90 days then they are very much behind the times and don't have a clue what they are talking about.
On a related note, DNA-PCR and RNA-PCR tests are not recommended by any HIV experts who know what they're talking about because of the high rate of false positives and other technical issues with that test. That is why they recommend the 28 day post exposure 4th generation duo test as the earliest possible time to get a test that can be considered conclusive.