Hi,

Was HIV 1&2 Abs/P24 Ag screen an antigen-antibody test that looked for HIV p24 antigen and antibodies to HIV-1 and HIV-2?

There was the word ENDOCRINOLOGY above my test result in my test report. What's that?

Opening comments: Yes, these tests are for both p24 antigen and antibodies to HIV1 and 2. I have no idea why your lab might have included the word endocrinology; it doesn't seem to relate directly to the test result. "Not detected" and "negative" mean the same thing.

To your numbered questions:

1,2. All the main AgAb tests perform equally well. All or most of the usual tests are marketed internationally, and for the most part the same tests are used in most industrialized countries. However, some tests, perhaps especially in developing countries, may have been developed regionally and not subjected to serious research as to their performance.

3-6. Negative results of the AgAb tests are conclusive 45 days or more after the last possible exposure, the interval advised by CDC. On this forum, we often round that off to 6 weeks; we are unaware of any reports of anyone testing negative at 42 days and positive at 45 days or more. The only exception is when anti-HIV drugs are taken to prevent infection, i.e. pre- or post-exposure prophylaxis (PrEP, PEP). If prophylaxis is unsuccessful, the time to positive test results is prolonged, at least to 6 weeks after the last drug dose, and some experts advise 3 months. There are no precise data on this issue. There are no significant differences between the venous (lab-based) and finger-stick tests. The rapid ("point of care") tests have a slightly higher rate of false positive results; therefore, all positive rapid tests should be confirmed with lab-based testing on venous blood.

7. These test types all seem to be equal in performance, within limits just discussed (i.e. venous/lab based versus rapid). You don't mention the oral fluids tests (Oraquick® and perhaps other brands outside the US):  they miss 2-5% of all HIV infections, no matter how long after exposure. In a way, it isn't the fault of the tests:  HIV antibody and p24 antigen concentrations are just lower in the oral fluids sampled than in blood.

8. Most experts (and we on this forum) consider 8 weeks conclusive for HIV2, although some experts may still recommend three months.

9. My understanding is that there have been a few case reports of persons who acquired HIV and HCV simultaneously in whom antibody detection was delayed. Usually there is no change in p24 Ag detection, and test performance is not affected. For the most part, these issues make no real world difference. Partly this is because simultaneous infection is rare:  contrary to popular beliefs (and internet buzz), HCV is NOT sexually transmitted except in men who have sex with men who participate in potentially traumatic anal sex practices (i.e. with likely blood exposure). For all other sexual exposures, simultaneous HIV and HCV infection simply isn't an issue. But it might rarely come up for persons infected by shared injection equipment, in whom both HIV and HCV are major risks.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD

Thanks for your reply. I certainly learned a lot from your forum.

So based on your reply, can I be confident that a single rapid (point of care) AgAb test at 8 weeks is sufficient to exclude both HIV-1 and HIV-2?

You seem to indicate that venous tests = lab-based tests. I wonder if some labs can also perform point-of-care tests using venous samples. Do you count these kinds of tests as "lab-based"?

By the way, why is there a strange whiteness behind my original texts? It changes my font and punctuation marks. Hopefully, it didn't affect your reading and understanding of my questions.

I don't know what kind of test my lab performed. I only know that the test was HIV 1&2 Abs/P24 Ag and was performed using my venous sample. So, assume that my lab performed a point-of-care (rapid) AgAb test (rather than a "lab-based" test involving specialized machinery) on my venous blood sample 8 weeks after exposure, can I be sure that I don't have HIV?

"I wonder if some labs can also perform point-of-care tests using venous samples." I suppose this could happen, but I see no reason and doubt it's a frequent practice. In any case, I see no reason why a rapid test would be any less accurate if performed on venous rather than finger-stick (capillary) blood. But if these thoughts continue to occur, why not call the lab and ask?

The display of your text had no unusual background or appearance on my computer. I'm sure I correctly understood all your comments and questions.

Do all HIV antigen-antibody tests (including the finger-stick tests) detect both IgG and IgM antibodies? Can I be sure that my HIV 1&2 Abs/P24 Ag screen test was for both IgG and IgM antibodies?

Thank you again for your help!

That completes the two follow-up exchanges included with each question and so ends this thread. I hope the discussion has been helpful. If you are pleased with the service you received, you might consider making a tax-deductible (if you're in the US) donation to our sponsor, the American Sexual Health Association www.ashasexualhealth.org. ASHA is the nation's leading nonprofit agency that supports sexual health with an emphasis on STI prevention.

Best wishes and stay safe.