What is an ELISA test for HIV?
Enzyme-Linked Immunosorbent Assays (ELISAs) or Enzyme Immuno-Assays
(EIAs) are the most widely used screening tests for HIV/AIDS and
detect antibodies produced by our body against HIV. Earlier test
kits used crude viral antigens to detect HIV antibodies but the
new kits use more specific recombinant protein and synthetic
peptide antigens, giving highly sensitive and specific test
results. Some new kits also detect viral antigens for an early
diagnosis.
What is a Simple/Rapid test for HIV?
Simple/Rapid tests are designed for use where a
preliminary/screening test result is required, are easy-to-use and
are especially useful in resource-limited countries. These are
quick and easy to perform – taking only 10 minutes to 2 hours –
and require little or no additional equipment. These are based on
agglutination, immuno-dot, immuno-chromatographic or immuno-filtration
techniques.
What is the difference between an ELISA and a Simple/Rapid test
for HIV? ELISAs are highly sensitive and specific, and are able to detect
HIV-1/ HIV-2 and their variants. They need skilled technicians,
sophisticated equipment and constant electricity supply. They are
more suitable for testing large numbers of samples per day, as
well as in blood banks or for surveillance studies.
The Simple/Rapid tests are also able to differentiate between
HIV-1 and HIV-2, and are better for emergency testing, and in
small laboratories with low numbers of tests per day.
How long after a possible exposure should I get tested for HIV? The ELISA or Rapid/Simple tests for HIV look for antibodies
produced by our body to fight HIV. The time period between HIV
infection and the appearance of detectable HIV antibodies is
called the window period, and usually lasts between 14-21 days.
Most people develop detectable antibodies within three months
after infection, but may rarely take upto six months. Therefore
testing is currently recommended six months after the last
possible exposure.
If your test is negative, and you were not exposed to risk of HIV
infection for six months before taking the test, it means you do
not have HIV infection.
Why is counselling important?
The pre-test information and counselling for an informed consent
are necessary before testing. The post-test and follow-up
counselling provide a good opportunity to learn more about HIV,
discuss your risks and learn how to avoid infection.
How is the test for HIV confirmed?
Confirmatory tests are used to verify whether specimens found
reactive with a screening test actually contain antibodies to HIV
or not. These are expensive and use the principle of line
immune-assays or Western blot. However, studies have shown that a
combination of two / three ELISAs and/or Simple/Rapid assays using
different antigens (whole viral lysate, recombinant antigens and
synthetic peptides) can provide results that are as reliable as
the confirmatory assays at a much lower cost.
A positive result means that you have HIV infection and could
benefit from special medical care. Additional tests can assess how
strong your immune system is and whether treatment is indicated.
Some people stay healthy for a long time with HIV infection, while
others develop serious illness and AIDS more rapidly.
Does an HIV positive test mean that the person tested has AIDS?
No, HIV is an unusual virus because a person can be infected with
it for many years and yet may appear to be perfectly healthy. But
the virus gradually multiplies inside the body and eventually
destroys the body's ability to fight off illnesses. It is still
not certain that everyone with HIV infection will get AIDS, but
most people with HIV will develop serious health problems, though
this may be after many years. A person with HIV may not know he is
infected but can unknowingly pass the virus on to other people.
What is the difference between HIV-1 and HIV-2?
There are two types of HIV that are currently known - HIV-1 and
HIV-2. Worldwide, the predominant virus is HIV-1. Both viruses are
transmitted by blood and blood products, sex, and from infected
mother to child. Although the disease caused by both is clinically
indistinguishable, HIV-2 is less easily transmitted and the period
between initial infection and illness is longer for HIV-2.
What are CD4 T-cells? CD4 T-cells are lymphocytes (white blood cells), also known as
helper T-cells, and co-ordinate the immune response. These CD4
T-cells are the main targets of HIV, which destroys infected CD4
T-cells, leading to an overall weakening of the immune system.
Lower numbers of circulating CD4 T-cells indicates a weakening of
the immune system and progression of HIV disease.
What is HIV viral load? The viral load refers to the number of viral particles found in
each millilitre (ml) of blood. The more HIV viral particles in the
blood, the faster the CD4 T-cells are likely to be destroyed and
the faster the progress toward AIDS. A result below 10,000 is
considered a low result. A result over 100,000 is considered a
high result.
How is disease progress monitored?
CD4 T-cell counts are used, together with the viral load test, to
get a complete picture about how the immune system is fighting the
virus. As HIV multiplies within the body, the viral load increases
and HIV destroys the CD4 T-cells, lowering the number of CD4
cells. Generally, the higher the HIV viral load, the more CD4
T-cells are being destroyed. The goal is to keep CD4 T-cell count
high and the viral load low.
The number of CD4+ T-cells and viral load will guide a patient and
their doctor in deciding when to start anti-viral treatment and
assess the response in patients on treatment.
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