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People are diagnosed with AIDS when they have certain signs or symptoms defined by the U.S. Centers for Disease Control and Prevention (CDC). The CDC's definition of AIDS includes:

  • Less than 200 CD4+ T cells per cubic millimeter of blood, compared with about 1,000 CD4+ T cells for healthy people. CD4+T cells are white blood cells that play an important role in the body's immune system. These cells are destroyed by HIV. Even when a HIV-positive person feels well and is not experiencing any symptoms of the disease, CD4+ T cells are being infected by HIV.
  • CD4+ T cells accounting for less than 14 percent of all lymphocytes, a type of white blood cell.
  • One of more of the illnesses listed below:
    • Candidiasis of bronchi, esophagus, trachea or lungs
    • Cervical cancer that is invasive
    • Coccidioidomycosis that has spread
    • Cryptococcosis that is affecting the body outside the lungs
    • Cryptosporidiosis affecting the intestines and lasting more than a month
    • Cytomegalovirus disease outside of the liver, spleen or lymph nodes
    • Cytomegalovirus retinitis that occurs with vision loss
    • Encephalopathy that is HIV-related
    • Herpes simplex including ulcers lasting more than a month or bronchitis, pneumonitis or esophagitis
    • Histoplasmosis that has spread
    • Isosporiasis affecting the intestines and lasting more than a month
    • Kaposi's sarcoma
    • Lymphoma that is Burkitt type, immunoblastic or that is primary and affects the brain or central nervous system
    • Mycobacterium avium complex or disease caused by M kansasii
    • Mycobacterium tuberculosis in or outside the lungs
    • Other species of mycobacterium that has spread
    • Pneumocystis jiroveci, formerly called carinii, pneumonia
    • Pneumonia that is recurrent
    • Progressive multifocal leukoencephalopathy
    • Salmonella septicemia that is recurrent
    • Toxoplasmosis of the brain, also called encephalitis
    • Wasting syndrome caused by HIV infection

Symptoms also may include anxiety, dementia, depression and insomnia.

Tests for HIV and AIDS

Blood tests are the most common way to diagnose the human immunodeficiency virus (HIV), the virus that causes acquired immunodeficiency syndrome (AIDS). These tests look for antibodies to the virus that are present in the blood of infected individuals. People exposed to the virus should get tested immediately.

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

Because it can take from six weeks to six months to develop antibodies to the virus, follow-up tests may be needed. Your doctor will ask about your symptoms, medical history and risk factors and perform a physical examination.

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.

Reviewed by health care specialists at UCSF Medical Center.