Diagnosis of HIV - HIV tests

chillibreeze writer — Suchitra Preetham

What is HIV?

HIV stands for Human Immunodeficiency Virus.

How does HIV spread?

HIV spreads through sexual fluids and blood. It can be contracted in the following ways:

Sex with an HIV infected person
Transfusion of infected blood and blood products
Infected mother to the baby
Sharing of infected needles with someone who is infected with HIV.

HIV TESTS

HIV is mainly diagnosed by screening blood for HIV antibodies. Our body produces antibodies for any bug that enters our system. These antibodies are specific and are used to detect the infection. The tests used to detect HIV antibodies are known as anti-HIV antibody tests.

ANTI-HIV ANTIBODY TESTS

SPOT TESTS: Spot tests or rapid tests. These tests are easy to perform and do not require sophisticated laboratory equipment. The results are interpreted visually and are available almost immediately. Though these tests are easy to perform, there is a chance of a false result.
ELISA: THE BEST TEST FOR HIV. ELISA is the most widely used anti-HIV antibody test. The ELISA test is usually performed as a batch. Unlike the Spot tests, the ELISA tests require specialized equipment and experienced personnel to perform and interpret the results. However the results of an ELISA test are accurate.
WESTERN BLOT: The Western blot is a confirmatory test for HIV. Almost always the ELISA test results are accurate; however there are times when the ELISA test does not give a clear positive or negative result. These are referred to as indeterminate results. Indeterminate results can be confirmed using a Western blot.

LIMITATIONS

Anti-HIV antibody tests can be performed only 4 to 6 weeks after contracting the HIV infection. This is because antibodies reach detectable levels only after 4 weeks. During this period, anti-HIV antibody tests will test negative. This is also called the WINDOW PERIOD.

Once produced, HIV antibodies persist for life.

DIAGNOSIS IN THE WINDOW PERIOD

WHICH TESTS

An early infection is detected by Direct or HIV Antigen detection tests. These tests detect the presence of the virus in the blood. Minute quantities of viruses can also be picked up by these tests. Examples are

Polymerase Chain Reaction (PCR) for proviral DNA
RT-PCR (Reverse Transcriptase-PCR) for viral RNA
p24 antigen test

WHEN TO GET TESTED

Antigen tests for HIV are expensive; as they require sophisticated laboratory equipment and personnel; therefore they are not common. However these tests are recommended

in the window period and
for babies born to HIV infected mothers

ELISA IS NOT THE BEST TEST FOR A NEWBORN BABY

Diagnosis of an HIV infection in babies born to HIV-infected mothers cannot be established by conventional anti-HIV antibody tests. This is because the presence of HIV antibodies in the newborn may not necessarily indicate infection of the baby, but may be due to the antibodies of the mother, which are passed on to the baby during pregnancy. These maternal antibodies (antibodies from the mother) circulate in the blood of the baby for up to 18 months. In order to determine HIV infection in a baby, direct tests such as the RT-PCR is recommended.

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—About our writer:

Suchitra says, "A born dreamer, I love flowers and chocolate. My life revolves around my husband and two adorable kiddies. I am passionate about my work as a medical microbiologist in a HIV/ AIDS center."