About HIV Test (2)

Rapid HIV tests

OraQuick HIV-1/2 rapid test kit
These tests are based on the same technology as ELISA tests, but instead of sending the sample to a laboratory to be analysed, the rapid test can produce results within 20 minutes.

Rapid tests can use either a blood sample or oral fluids. They are easy to use and do not require laboratory facilities or highly trained staff.

All positive results from a rapid test must be followed up with a confirmatory test, the results of which can take from a few days to a few weeks.

Antigen test (P24 test)
Antigens are the substances found on a foreign body or germ that trigger the production of antibodies in the body. The antigen on HIV that most commonly provokes an antibody response is the protein P24. Early in HIV infection, P24 is produced in excess and can be detected in the blood serum (although as HIV becomes fully established in the body it will fade to undetectable levels).

P24 antigen tests are not usually used for general HIV diagnostic purposes, as they have a very low sensitivity and they only work before antibodies are produced in the period immediately after HIV infection. They are now most often used as a component of 'fourth generation' tests.

Fourth generation tests
Some of the most modern HIV tests combine P24 antigen tests with standard antibody tests to reduce the ‘diagnostic window’. Testing for antibodies and P24 antigen simultaneously has the advantage of enabling earlier and more accurate HIV detection.

In the UK, fourth generation tests are the primary recommendation for HIV testing among individuals, but are not offered by all testing sites. During June 2010, the FDA approved the first fourth generation test in the United States.

PCR test
A PCR test (Polymerase Chain Reaction test) can detect the genetic material of HIV rather than the antibodies to the virus, and so can identify HIV in the blood within two or three weeks of infection. The test is also known as a viral load test and HIV NAAT (nucleic acid amplification testing).

Babies born to HIV positive mothers are usually tested using a PCR test because they retain their mother's antibodies for several months, making an antibody test inaccurate. Blood supplies in most developed countries are screened for HIV using PCR tests. However, they are not often used to test for HIV in individuals, as they are very expensive and more complicated to administer and interpret than a standard antibody test.

Home sampling
With a home sampling kit, a person can take a sample (usually a blood sample) and send it to a laboratory for testing. They can phone up for the results a few days later. If the result is positive then a professional counsellor will provide emotional support and referrals. The main advantages of home sampling are convenience, speed, privacy and anonymity.

Home testing
A home self-test involves a person conducting a rapid antibody HIV test in their home. The person takes either a blood or saliva sample and can interpret the result within minutes. A positive result may require a further confirmatory blood-test in a clinic.

UNAIDS suggest that home testing could be a partial solution in parts of the world where there is a severe number of people living with HIV who don’t know their status. In many health-care settings people worry about their test results remaining confidential and supervised home-based testing has the potential to help overcome some of these issues. A study in Kenya has also shown that home-based counseling and testing (HBCT) can be the most effective gateway to getting people who test positive into care and treatment.