Hiv Aids Testing

HIV testing accurately diagnoses the presence of the virus. However, in order for an HIV test to be effective, it must be administered about two months after possible contact with HIV. This allows the body to produce a concentration of antibodies sufficient for the test to be accurate.

Do You Need an HIV Test?

An HIV test is not a routine medical procedure: only people who believe they have been exposed to the virus receive HIV testing. If any of the following factors are a concern, HIV testing is recommended:

  • an unplanned pregnancy
  • maternal HIV infection
  • sexual assault
  • sexual contact with an HIV positive individual or an intravenous drug abuser
  • needles shared for drug abuse, tattoos or body piercing
  • unprotected sex (anal, vaginal or oral).

In addition, HIV testing is recommended for anyone who has lost consciousness while intoxicated or high or has no memory of a particular period of time. People with a history of any sexually transmitted disease should also receive an HIV test. Anyone who has been diagnosed with any of the following conditions should be tested:

  • chlamydia
  • genital herpes
  • gonorrhea
  • hepatitis
  • trichomoniasis.

HIV Testing and Antibodies

HIV testing examines the blood for signs of HIV antibodies produced by the body in an attempt to fight the infection. Unfortunately, HIV testing does not usually detect HIV antibodies immediately after infection. The body requires some time to produce sufficient antibodies for HIV testing to accurately detect the presence of the virus.

In the majority of cases, HIV antibodies are present in detectable amounts within two to twelve weeks of infection. An HIV test may need to be repeated if performed too soon after infection.

Making a Definitive Diagnosis

Two HIV tests exist: the ELISA (enzyme-linked immunosorbent assay) and the Western Blot test.

ELISA is usually the first choice for HIV testing, but anyone requiring an HIV test will also receive the Western Blot test. Both tests are required for a definitive HIV diagnosis, as ELISA has been known to yield false positives (indicating the presence of HIV antibodies when none are actually present).

For both tests, a small sample of blood is necessary. In the United States, oral, needle-free versions are available.

HIV Testing and At-Risk Babies

Babies born to HIV positive mothers must receive HIV testing, although accurate results may not be available for up to eighteen months after birth.

All babies born to HIV positive mothers will have HIV antibodies at birth, as antibodies from the mother pass into the baby’s bloodstream. This does not, however, mean that the child is infected with HIV. Roughly 25 percent of non-breastfeeding babies born to HIV positive mothers end up infected with HIV.

Maternal HIV antibodies may be present in an infant for as long as eighteen months, masking whether the child is also producing antibodies. During this time HIV testing is not possible, as the maternal antibodies will yield a false positive on any HIV test.

Maternal HIV antibodies make the early diagnosis of infant HIV difficult, especially if the disease is asymptomatic in the first months of life.

HIV Testing without Antibodies

HIV testing that tests directly for the presence of the HIV virus, rather than HIV antibodies, is also available. The polymerase chain reaction HIV test (PCR) test detects the “viral load,” by measuring levels of viral DNA, and can be performed at any time after infection.

While PCR HIV testing is accurate, in most cases, its high cost and limited availability do not make it a viable alternative to antibody-detecting HIV tests in most instances.

Resources

American Association for Clinical Chemistry. (reviewed 20 July 2005). HIV antibody.

HIV InSite. (September 2004). Should I get tested for HIV?

HIV InSite. (September 2004). What happens when you get tested for HIV?

National Institute of Allergy and Infectious Diseases. (updated 4 April 2005). HIV infection and AIDS: An overview.

Medicomm. (nd). ELISA tests.