HIV P24 Ag/Ab Test, Duo Test, Combo Test at our Clinic
Let’s first get some basics right:
Duo Test = Combo Test = P24 Ag/Ab test
All these terms refer to the same thing. Basically it is a test that simultaneously tests for the HIV P24 Antigen and the HIV antibody.
The HIV P24 antigen is a small piece of protein that is found on the capsule of the HIV virus. When a person is infected with HIV, these bits of protein can be found floating in the blood. The HIV P24 test is a test that detects these bits of protein. This test was first developed as a HIV screening test but rapidly ran out of favor due to the development of more advanced NAAT tests. (For more details on NAAT testing please read: http://www.drtanandpartners.com/nucleic-acid-amplification-testing-naat/)The window period for P24 testing is also very small. This test alone is only accurate for between 3 and 6 weeks post exposure. So it is a test with very limited applications unless combined with the HIV antibody test. The presence of P24 Antigens in the blood indicates a recent HIV infection.
We all already know that the HIV antibody test becomes quite reliable at 4 weeks and as good as conclusive at 6 weeks. Although most health authorities still recommend a 3 months window period. So putting these 2 tests together gives you a very powerful tool to diagnose HIV infection in as little as 3 weeks. Personally I prefer to conduct the Combo test at 4 weeks because I believe that is when the level of P24 antigen peaks in the blood giving us maximum accuracy.
In our clinic, we use the Determine™ HIV-1/2 Ag/Ab Combo Test by Alere. It is a rapid test that takes only 20 minutes for us to get results. We are also approved to conduct this test as part of the Anonymous HIV testing Program.
The test is conducted very much like the HIV antibody test. All we need is blood from a finger prick. (For more details on Anonymous HIV Testing at our clinic please read: http://www.drtanandpartners.com/anonymous-hiv-testing-at-our-clinic/)
The performance characteristics for the Determine™ HIV-1/2 Ag/Ab Combo Test by Alere are as follows:
1. 100% sensitivity across 1179 samples including HIV-1 Group O and HIV-2.
2. 2 to 20 days earlier detection of HIV infection compared to the Determine™ HIV-1/2 Antibody (3rd Generation) Test by Alere.
3. 99.6% specificity. i.e. 0.4% false positive rate.
So the Combo Test has many advantages including:
1. Earlier detection of HIV infection.
2. Rapid (20 minutes)
The only problem is that it costs more.
About Dr. Tan
Dr. Tan graduated from the National University of Singapore in 2001. His residency was in the two largest public hospitals in Singapore; Tan Tock Seng Hospital and Singapore General Hospital.