Detection of HIV – By ELISA and Western Blot technique


Human Immunodeficiency virus (HIV) is an infectious disease that attack the immune system. If not treated, it can develop into Acquired Immunodeficiency Syndrome (AIDS) which is a prolonged and fatal illness. HIV is spread through vaginal, oral, or anal sexual contact. It is also spread through blood, blood factor products,injection, and through breast milk.

Diagnosis of HIV infection by ELISA / Western blot technique

HIV ELISA / Western blot is a set of blood tests used to diagnosis chronic infection with human immuno deficiency virus (HIV). The Enzyme- Linked Immunosorbent Assay (ELISA or EIA) is the first test that your doctor will prescribed to screen HIV. ELISA and the Western blot test detect antibodies in your blood. Antibodies are proteins that your immune system produce in response to the presence of foreign substances such as viruses. If you test positive for HIV on the ELISA test, you will have to carry out Western blot test after that to confirm HIV infection.

Sometimes, HIV does not show positive test on ELISA which can happen if someone is in the early stages of the infection where body does not produces enough antibodies to the virus for the test to detect. This early stage of the infection is referred as the “window period”. According to the Centres for Disease Control and Prevention, window period usually is in between two and eight weeks. However in rare cases it can take long as six months to develop antibodies. However, sometimes there are false positives with the ELISA test also such as diseases like Lyme disease, syphilis or lupus may produce a false positive.

Hence these both test ELISA and Western Blot require a high degree of both sensitivity and specificity. In the United States, this is achieved using algorithm combining two tests for HIV antibodies. If antibodies are detected by an initial test based on the ELISA method, then a second test using Western blot determines the size of the antigens. The combination of these two methods is considered to be highly accurate.


How ELISA test is performed?

Enzyme- linked immunosorbent assay was the first screening test employed for detection of HIV. In this test the patient serum is diluted and applied to membrane coated with HIV antigens. If antibodies to HIV antigens are present in the serum, they will bind to them. The ELISA reagent will detect the bound antibodies and the color change will indicate the positive result. ELISA is a faster and a very sensitive test used for detection of HIV infection.


How is Western blot test performed?

Like ELISA test, Western blot is also an antibody detection test. But unlike ELISA, HIV antigens are first separated by applying electric current and then immobilized (coated to membrane) in Western blot. Now the patient’s serum is applied to the membrane containing well separated HIV proteins (antigens)and if antibodies are present in patient’s serum, they will bind to specific antigens. Antibodies that do not attach are washed away. The western blot rarely produces false- positive result and hence is used to confirm the presence of HIV infection in people who test positive first with ELISA.

Once the HIV test is detected positive it is highly recommended to seek immediate medical treatment for the infection, so that you can live full and long life. The earlier you detect your HIV status, the earlier you can start treatment to prevent further more health complications and transmission of virus to others.



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