HOW IS HIV DIAGNOSED?

Laboratory investigations:

1. ELISA tests – to detect antibodies. The most common test to detect HIV antibodies is the ELISA test, which is abbreviation of ENZYME LINKED IMMUNO SORBENT ASSAY. ELISA tests is preferred as an initial test for HIV testing mainly because it is simple and sensitive.
   
   It is therefore suitable for testing large number of blood samples. It is important to remember that there are several ELISA kits available commercially and not all of them confirm to recommended guidelines. It is therefore recomended that the ELISA test is performed in laboratories approved or supported by the National AIDS Control Organisation.
   
   The Government of India has recommended that only if two consecutive and separate ELISA test have indicated the presence of antibodies, further tests to confirm HIV infection are recommended. These tests are expensive and therefore many medical practitioners recommend three consecutive ELISA tests to be done instead of doing a confirmatory test.
   
   If each of the tests indicates the presence of HIV antibodies, the tested person is said to have HIV infection. As mentioned earlier, a person infected with HIV develops antibodies only after about 3 to 6 weeks. The period between contracting the the actual infection and the time when antibodies appear in the blood is called the window period. ELISA test will be negative if the blood is tested in the window period.
   
   
2. The most common test used to confirm HIV infection is the Western Blot test. This test also detects antibodies to HIV. A western blot test is said to be positive if the test shows reactivity to at least two components of the virus. A negative test is one, which does not indicate antibodies to any of the components of the virus.
   
   In case there is reactivity to one or more antigens only, or if there is weak reaction, the test results is said to be doubtful. It is important to remember that about 15% people who are not infected with HIV can also have doubtful test result. This is why Western Blot test is recommended only after two consecutive ELISA tests have been positive.
   
   
3. Viral Load - to identify the virus and estimate it’s number in the body. The most common test to detect HIV itself is called polymerase chain reaction or PCR test. These tests indicate the presence of the virus in newborn babies or adults within a week of their getting HIV infection. The PCR test can also estimate the number of viruses in the blood and therefore are used to assess the progress of the disease.
   
   
4. CD4 (T4) count – to estimate the number of T cells in the blood. Estimating the number of T cells in the blood or the total CD-4 count in the blood is used for identifying the stage of HIV infection, plan the most suited treatment option and establish the diagnosis of AIDS. It can also be used to decide whether specific preventive measures are desirable for opportunistic infections or not. This is because a decline in CD4 cells indicates increased risk of getting infections. A CD4 count of less than 200 is diagnostic of full blown AIDS. It is also used as marker for response to treatment given.

WHEN IS A BLOOD TEST TEST FOR HIV RECOMMENDED?

The HIV test results can have major impact on the psychological status of the person tested, family, relationships with other members, employment opportunities, etc. This is why HIV testing should not be done without informed consent. This means that the person being tested should understand the consequences of the test results. It is also important to keep the test results confidential.

HIV testing without consent is done for all blood samples collected for transfusion and during sentinel surveillance. The test results are however confidential and anonymous. Testing the blood for HIV without informed consent is ethically wrong and is strongly discouraged by the Government of India and all agencies involved in prevention and control of HIV/AIDS in India.

WHAT DO HIV RESULTS MEAN?

Negative test result:

• The person tested does not have HIV infection, or
• The person tested has HIV infection but is in Window Period.

Positive test result in a person above 15 months of age:

• The person tested has antibodies against HIV in his/her blood.
• Presence of antibodies indicates that the person has HIV infection. He/she can therefore spread the virus to others.

• The child has received antibodies to HIV from his/her mother.
• The HIV antibodies acquired by a child from the mother normally disappear by 15 months.
• HIV test needs to be repeated after the child is 15 months old in order to find out if the child has got HIV infection or not.