infections
Human Immunodeficiency Virus (HIV) Infection
Diagnosis of HIV Infection
Tests to detect antibodies to the HIV virus in a sample of blood or saliva Tests to detect HIV RNA in a sample of blood Early diagnosis of HIV infection is important because it makes early treatment possible. Early treatment enables infected people to live longer, be healthier, and be less likely to transmit HIV to other people. Doctors usually ask about Transmission of HIV Infection (such as possible exposure in the workplace, high-risk sexual activities, and use of injected street drugs) and about symptoms (such as fatigue, rashes, and weight loss). Doctors also do a complete physical examination to check for signs of opportunistic infections, such as swollen lymph nodes and white patches inside the mouth (indicating thrush), and for signs of Kaposi sarcoma of the skin or mouth. If doctors suspect exposure to HIV infection, they do a screening test for HIV. Doctors also offer a screening test to all adults and adolescents, particularly pregnant women, regardless of what their risk appears to be. Anyone who is concerned about being infected with HIV can request to be tested. Such testing is confidential and often free of charge. The current (4th-generation) combination screening test tests for two things that suggest HIV infection: Antibodies to HIV HIV antigens (p24 antigen) Antibodies are proteins produced by the immune system to help defend the body against a particular attack, such as that by HIV. Antigens are foreign substances that can trigger an immune response. The body takes several weeks to produce enough antibodies to be detected by the test, so results of the antibody test are negative during the first few weeks after the virus enters the body (known as the "window period" of acute HIV infection). However, results of the p24 antigen test can be positive as early as 2 weeks after the initial infection. The combination tests can be done quickly by a laboratory. Also, a version of these tests can be done in a doctor's office or clinic (called bedside testing). If results are positive, doctors do a test to distinguish HIV-1 from HIV-2 and a test to detect the amount of HIV RNA in the blood (the viral load). The combination screening test is quicker and less complex than older screening tests, which use enzyme-linked immunosorbent assay (ELISA) to detect HIV antibodies and then confirm positive results using a separate, more accurate, specific test such as the Western blot test. Other, older rapid bedside tests are also available. These tests can be done using a sample of blood or saliva. If results of these rapid screening tests are positive, they are confirmed by ELISA (with or without Western blot) or by repetition of one or more other rapid tests. If people at low risk have a negative test result, the screening test is not repeated unless their risk status changes. If people at the highest risk have a negative test result (especially if they are sexually active, have several sex partners, or do not practice safer sex), testing should be repeated every 6 to 12 months. HIV RNA tests can confirm positive results of an antibody test or detect evidence of HIV infection when antibody test results are negative. HIV RNA tests often use techniques to produce many copies of an organism's genetic material (called nucleic acid amplification). These tests can detect very small amounts of HIV RNA in blood and are very accurate. If HIV infection is diagnosed, blood tests should be done regularly to measure the following: CD4 count Viral load If the CD4 count is low, people are more likely to develop serious infections and other complications of HIV such as certain cancers. Viral load helps predict how fast the CD4 count is likely to decrease over the next few years. These two measurements help doctors determine How soon to start antiretroviral medications What effects treatment is likely to have Whether other medications may be needed to prevent complicating infections With successful treatment, the viral load falls to very low levels within weeks, and the CD4 count begins a slow recovery toward normal levels. AIDS is diagnosed when the CD4 count falls below 200 cells per microliter of blood or when extreme wasting or certain serious opportunistic infections or cancers develop. Various tests may be done to check for conditions that can accompany HIV infection. These tests include the following: Bone marrow aspiration and biopsy: To further evaluate low blood cell counts (including anemia), which may be due to lymphomas, cancers, and opportunistic infections Computed tomography (CT) with a contrast agent or magnetic resonance imaging (MRI): To check for damage to the brain or spinal cord 