HOW IS HIV DIAGNOSED?
- 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
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
- 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.
- Viral Load - to identify the virus and estimate its 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.
- 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
- Presence of antibodies indicates that the person
has HIV infection. He/she can therefore spread the virus to others.
Positive test result in a person under 15 months of age:
- The child has received antibodies to HIV from his/her
- 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.