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HIV
Diagnosis

Blood tests are the most common way to diagnose HIV. These tests look for antibodies to the virus that the body creates in an attempt to fight the virus.

People exposed to the virus should get tested immediately, although it can take the body anywhere from six weeks to a year to develop antibodies to the virus. Follow-up tests may be needed depending on the initial time of exposure.

Early testing is crucial. If you test positive for the virus, you and your doctor will discuss and develop a treatment plan that can help fight HIV and ward off complications. Early testing also can alert you to avoid high-risk behavior that can spread the virus to others.

Most health care providers offer HIV testing, often with appropriate counseling. Anonymous and free testing also is available. During testing, your doctor will ask about your symptoms, medical history and risk factors, and perform a physical examination.

Tests for HIV and AIDS

The primary tests for diagnosing HIV and AIDs include:

  • ELISA Test — ELISA, which stands for enzyme-linked immunosorbent assay, is used to detect HIV infection. If an ELISA test is positive, the Western blot test is usually administered to confirm the diagnosis. If an ELISA test is negative, but you think you may have HIV, you should be tested again in one to three months.

    ELISA is quite sensitive in chronic HIV infection, but because antibodies aren't produced immediately upon infection, you may test negative during a window of a few weeks to a few months after being infected. Even though your test result may be negative during this window, you may have a high level of the virus and be at risk of transmitting infection.
  • Home Tests — The only home test approved by the U.S. Food and Drug Administration is called the Home Access Express Test, which is sold in pharmacies.
  • Saliva Tests — A cotton pad is used to obtain saliva from the inside of your cheek. The pad is placed in a vial and submitted to a laboratory for testing. Results are available in three days. Positive results should be confirmed with a blood test.
  • Viral Load Test — This test measures the amount of HIV in your blood. Generally, it's used to monitor treatment progress or detect early HIV infection. Three technologies measure HIV viral load in the blood: reverse transcription polymerase chain reaction (RT-PCR), branched DNA (bDNA) and nucleic acid sequence-based amplification assay (NASBA). The basic principles of these tests are similar. HIV is detected using DNA sequences that bind specifically to those in the virus. It is important to note that results may vary between tests.
  • Western Blot — This is a very sensitive blood test used to confirm a positive ELISA test result.

For more information, please see FAQ: HIV Testing.

Reviewed by health care specialists at UCSF Medical Center.