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Tests and diagnosis
By Mayo Clinic staffHIV is diagnosed by testing your blood or oral mucus for the presence of antibodies to the virus. The Centers for Disease Control and Prevention (CDC) encourages voluntary HIV testing as a routine part of medical care for all adolescents and adults ages 13 to 64. Although the CDC says that everyone should be tested at least once, yearly testing is recommended only for people at high risk of infection.
Unfortunately, HIV tests aren't accurate immediately after infection because it takes time for you to develop these antibodies — usually about 12 weeks. In rare cases, it can take up to six months for an HIV test to become positive.
ELISA and Western blot tests
For years, the only available test for HIV was the enzyme-linked immunosorbent assay (ELISA) test that looked for antibodies to the virus in a sample of your blood. If this test was positive — meaning you had antibodies to HIV — the same test was repeated. If the repeat test was also positive for HIV antibodies, you'd then have another confirming blood test called the Western blot test, which checks for the presence of HIV proteins. The Western blot test was important because you may have non-HIV antibodies that cause a false-positive result on the ELISA test. Combining the two types of tests helped ensure that the results were accurate, and you'd receive a diagnosis of HIV only if all three tests were positive. The downside is that it can take up to two weeks to get the results of the ELISA and Western blot tests, a period of time that can take an emotional toll and that discouraged many people from returning to get their test results.
Rapid tests
Now, several rapid tests can give highly accurate information within as little as 20 minutes. These tests look for antibodies to the virus using a sample of your blood or fluids collected on a treated pad that's rubbed on your upper and lower gums. The oral test is almost as sensitive as the blood test and eliminates the need for drawing blood. A positive reaction on a rapid test requires a confirming blood test. And because the tests are relatively new and were originally approved for use only in certified laboratories, they may not be available everywhere.
Home tests
Currently, the Food and Drug Administration (FDA) has approved only one HIV test for home use. The Home Access HIV-1 test, marketed by Home Access Health, is as accurate as a clinical test, and all positive results are automatically retested.
Unlike a home pregnancy test, you don't evaluate the test yourself. Instead, you mail in a drop of your blood, then call a toll-free number to receive your results in three to seven business days. This approach ensures your privacy and anonymity — you're identified only by a code number that comes with your kit. The greatest disadvantage is that you're not offered the counseling that you typically receive in a clinic or doctor's office, although you're given referrals for medical and social services. No matter what type of test you choose, if you test positive for an HIV infection, tell your sexual partner or partners right away so that they can be screened and take steps to protect themselves.
If you receive a diagnosis of HIV/AIDS, your doctor will use a test to help predict the probable progression of your disease. This test measures the amount of virus in your blood (viral load). Studies have shown that people with higher viral loads generally fare more poorly than do those with a lower viral load. Viral load tests are also used to decide when to start and when to change your treatment.
