What is an ELISA HIV Test
ELISA stands for Enzyme Linked Immunosorbent Assay. It is the most common HIV test and is used up till this day to detect HIV infection. This test detects the presence of HIV antibodies in the bloodstream. The immune system forms these proteins known as antibodies so that immune cells can target and destroy the invading pathogen – in this case, HIV.
A positive result should warrant another ELISA test to ensure that sample was not tainted or mixed up. Two positive ELISA tests means that a confirmatory test known as the Western Blot should be done. In many countries, the presence of one positive ELISA test will lead to a confirmatory Western Blot test.
HIV Window Period and Seroconversion
The process of developing antibodies against the virus may take 3 to 12 weeks to occur and is known as seroconversion. The period before seroconversion is referred to as the “window period”.
While the average time for seroconversion to occur is 8 weeks, most people will have antibodies present within 5 to 6 weeks after exposure. Rarely, seroconversion may take up to 6 months. There are a few cases globally where this had occurred but other factors may have been partly responsible for these accounts.
Ideally a sexually active adult should have an HIV test every 6 months even if HIV infection is not suspected or the first signs of HIV are not present.
Does a Positive ELISA Test Mean That You Are HIV-Positive?
No. There are other diseases that produce antibodies which may register a positive ELISA result. This is called a false-positive result.
These other diseases may include :
- Lyme disease
- Lupus and possibly other types of autoimmune diseases.
- Certain blood and immune birth defects.
There are other possibilities (medical conditions and prophylactic therapies) that may give rise to non-HIV antibodies which could contribute to a false-positive result. This is rare these days with modern testing methods. However, a Western blot test should ALWAYS be done to confirm HIV infection.
Does a Negative ELISA Test Mean That You Are HIV-Negative?
No. You may be in the “window period” where seroconversion has not as yet occurred. Further testing should be considered in 3 to 6 weeks after a negative result.
With modern testing methods, a negative result by the 6th to 8th week after exposure is usually an indication of being HIV-negative. A negative result at 12 weeks after exposure is usually considered conclusive of being negative.
What is the Western Blot Test?
The Western blot tests for the presence of the certain proteins. It is conclusive for a diagnosis of HIV when combined with positive ELISA test results.
Western blot testing can be done for other infectious diseases and results may take up to 1 to 2 weeks depending on the availability of facilities. Private laboratories will have results available within 48 to 72 hours. The cost of the Western blot test is higher than an ELISA test so it is usually reserved only as a confirmatory test.
Does a Negative Western Blot Test Mean That You Are HIV-Negative?
No. During the “window period” (prior to seroconversion), the Western blot test may not register a positive result. The test should then be repeated in 3 to 6 weeks time.
In the event that an ELISA test is positive and the Western blot test is negative, your doctor will need to consider further testing to identify the cause of the false-positive ELISA result. PCR (polymerase chain reaction) testing may also be considered to confirm a diagnosis of HIV infection. This test detects the presence of nucleic acids (HIV RNA and DNA) to confirm HIV infection.
Article reviewed by Dr. Greg. Last updated on June 8, 2010