Question
Which test shall I take for HIV – antibody or PCR?
2 January 2008. Related: All topics, HIV testing.
I have read with much confusion over taking either an antibody or a pcr test. Which one should I take and when would the result be conclusive? I have read that even taking antibody test at 6 months is not conclusive, therefore better to take a pcr. Please help.
Answer
Thank you for your question. I totally understand your confusion about the various HIV tests available and how to distinguish which one you should take.
The HIV PCR test is a sensitive test but is only recommended in specific circumstances. Viral load tests are not approved to diagnose HIV.
It is not normally used to test HIV in adults because they are less accurate, take longer to get a result and are more complicated and
You should not worry about the different numbers, as long as both results are negative.
I took the duo test twice – at 25 days the result was 0.13 and at 29 days it was 0.18 – this increase has got me quite worried. While both results are negative – why the increase. Is it because I developed a bad cold from day 28 onwards?
Would appreciate your opinion.
Even though PCR is not an approved test for diagnosing HIV, the negative result is likely to mean that you have not been infected.
Your plan to take an atibody test to confirm this at 3 and 6 months is good advice.
A further PCR test is unlikely to give you any additional information.
I do not have data on sensitivity of PCR as a diagnostic test, by time since exposure. Usually it is pretty sensitive if you get a positive result that is over 5,000 copies/mL. In early infection this would be common. A negative result is a good indication that no virus was found.
I had an HIV PCR test done 18 days after possible exposure. It came back negative. I will get the standard done at 3 and 6 months. If I got the PCR test a little after 28 days will the results be very reliable? Also, how reliable are the PCR results at 18 days?
Yes, 6 months positive cases are really rare, but yes, they exist. They are less than 0.01% of cases.
Some epidemiological studies suggest that taking longer than 6 months to generate an antibody response is considerable smaller.
How rare are these 6 months positive cases? If someone test at 6 months negative, is the result 100% reliable?
Thank you for your answer. I have always come across the statement of 6 months to test positive is very rare. Would you please help to better understand it? In what circumstances would these rare cases happen? Do they really happen or is it only a safety factor to double the actual window period time frame? What about after 6 months, a year? PLease help.