Diagnostic Tests for HIV/AIDS


Diagnostic Test list for HIV/AIDS: The list of diagnostic tests mentioned in various sources as used in the diagnosis of HIV/AIDS includes:

  • HIV antibody blood test - though the test sometimes cannot detect HIV for 6 months; sometimes not till 15 months for infected infants.
  • Immune tests
  • PAP smears - needed more often to check for cervical cancer in women.

Tests and diagnosis discussion for HIV/AIDS: HIV infection is often difficult to diagnose in very young children. Infected babies, especially in the first few months of life, often appear normal and may exhibit no telltale signs that would allow a definitive diagnosis of HIV infection. Moreover, all children born to infected mothers have antibodies to HIV, made by the mother's immune system, that cross the placenta to the baby's bloodstream before birth and persist for up to 18 months. Because these maternal antibodies reflect the mother's but not the infant's infection status, the test is not useful in newborns or young infants.

In recent years, investigators have demonstrated the utility of highly accurate blood tests in diagnosing HIV infection in children 6 months of age and younger. One laboratory technique called polymerase chain reaction (PCR) can detect minute quantities of the virus in an infant's blood. Another procedure allows physicians to culture a sample of an infant's blood and test it for the presence of HIV.

Currently, PCR assays or HIV culture techniques can identify at birth about one-third of infants who are truly HIV-infected. With these techniques, approximately 90 percent of HIV-infected infants are identifiable by 2 months of age, and 95 percent by 3 months of age. One innovative new approach to both RNA and DNA PCR testing uses dried blood spot specimens, which should make it much simpler to gather and store specimens in field settings.1

Because early HIV infection often causes no symptoms, a doctor or other health care provider usually can diagnose it by testing a person's blood for the presence of antibodies (disease-fighting proteins) to HIV. HIV antibodies generally do not reach detectable levels in the blood for one to three months following infection. It may take the antibodies as long as six months to be produced in quantities large enough to show up in standard blood tests.

People exposed to the virus should get an HIV test as soon as they are likely to develop antibodies to the virus - within 6 weeks to 12 months after possible exposure to the virus. By getting tested early, people with HIV infection can discuss with a health care provider when they should start treatment to help their immune systems combat HIV and help prevent the emergence of certain opportunistic infections (see section on treatment below). Early testing also alerts HIV-infected people to avoid high-risk behaviors that could spread the virus to others.

Most health care providers can do HIV testing and will usually offer counseling to the patient at the same time. Of course, individuals can be tested anonymously at many sites if they are concerned about confidentiality.

Health care providers diagnose HIV infection by using two different types of antibody tests, ELISA and Western Blot. If a person is highly likely to be infected with HIV and yet both tests are negative, the health care provider may request additional tests. The person also may be told to repeat antibody testing at a later date, when antibodies to HIV are more likely to have developed.

Babies born to mothers infected with HIV may or may not be infected with the virus, but all carry their mothers' antibodies to HIV for several months. If these babies lack symptoms, a doctor cannot make a definitive diagnosis of HIV infection using standard antibody tests until after 15 months of age. By then, babies are unlikely to still carry their mothers' antibodies and will have produced their own, if they are infected. Health care experts are using new technologies to detect HIV itself to more accurately determine HIV infection in infants between ages 3 months and 15 months. They are evaluating a number of blood tests to determine if they can diagnose HIV infection in babies younger than 3 months. 2

A window period is a recommended waiting period to receive an accurate HIV test result. Generally, it is a six-week to six-month period from the moment of your last unsafe sex encounter to the moment that you receive a HIV screening. This is the time your body uses to create antibodies in the blood stream, which signify exposure to HIV. This process is known as seroconversion.

It is important when receiving an HIV test to ask what kind of test is being used. Whenever someone is screened for HIV, two types of tests are used. They are, 1) a reactive test, and 2) a confirmatory test. A reactive HIV test indicates if HIV antibodies are in the blood (such as the Elisa Test). A reactive test may give a false positive reading to anyone with kidney or renal failure, to a woman that has had multiple pregnancies, anyone receiving the influenza vaccine, or to anyone that has received gamma globulin. When a reactive test has a negative result, that means no HIV antibodies were detected. But in order to receive an accurate reading, the CDC recommends you wait a specific window period: six weeks to six months and either abstain from all sexual activity, or practice safe sex in every sexual situation, and then get a confirmatory test, such as the Western Blot Test.

A confirmatory test (such as the Western Blot) provides the HIV status of a person. A positive test result on a confirmatory test means that the person has been infected with HIV, has HIV antibodies in his or her blood, and can infect others.

Being HIV positive does not mean that the person has acquired immunodeficiency syndrome (AIDS) or that it is 100% guaranteed that the person will get AIDS, though research has shown that it is likely to happen. 3

Diagnosis of HIV/AIDS: medical news summaries: The following medical news items are relevant to diagnosis of HIV/AIDS:

1. excerpt from Backgrounder - HIV Infection in Infants and Children: NIAID
2. excerpt from HIV Infection and AIDS, An Overview, NIAID Fact Sheet: NIAID
3. excerpt from Women and HIV-AIDS: NWHIC

Last revision: April 2, 2003

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