ELISA Test For HIV guide


What is it?

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.

How is ELISA different from a Simple/Rapid test?

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?

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 being HIV positive mean one 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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