Question
How do you interpret accuracy of HIV tests?
11 March 2008. Related: All topics, HIV testing.
On this website, it has been stated that HIV antibodies are present in 95% of people within 30 days after infection. Are they detectable by the antibody test at this stage also?
Why then is it recommended that the test be carried out after 3 months? Is this because after 3 months antibodies will be present in 100% of infected people? (give or take the odd very rare occurrence of people developing antibodies after this period)
Am I right in saying that a negative antibody test 6 weeks after possible exposure to HIV would mean around a 98% chance that the person is not infected with HIV, given that antibodies would have developed (and would be detected) in about 98% of infected people by this stage ?
Answer
To your first question: yes, guidelines estimate that about 95% of people have HIV antibodies within about four weeks.
To your second question: after 3 months, antibodies will be detectable in more than 99.999% of people who have been infected with HIV.
To your third question: yes, you are right. At any time time between 30 an 90 days, the percentage will gradually increase from 95% to close to 100%.