Rapid HIV tests
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.1 During June 2010, the FDA approved the first fourth generation test in the United States.2
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.
HIV home sampling and HIV home testing
It is generally recommended that an HIV test is carried out in a healthcare setting. However, in some countries home sampling and home testing kits are available.
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.
There is one company in the USA that offers an FDA-approved home sampling kit for HIV.3 Many home sampling kits that have not been approved by the FDA are being marketed online.4
There is also a company in the UK that offers home sampling services using oral fluid instead of blood.5 If a person’s test result is positive they will need a follow up blood-test at a clinic.
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 will require a further confirmatory blood-test in a clinic.
In many countries it is illegal to sell HIV test kits to the public. If a test is purchased over the internet, there is no guarantee that the test kit is genuine or will provide accurate results.
There is currently a debate about allowing the kits to be sold in America and the UK. AVERT opposes the legalisation of the sale of home testing kits in the UK because of the lack of post-test counselling.
No comments:
Post a Comment