Q: Is a negative result obtained from a HIV DNA PCR test result, wherein the sample is given 72 hours post exposure, a true & conclusive negative? What is the right time to give a sample for HIV testing after suspected exposure?

A:No. The HIV RNA appears in blood around 15 days post exposure depending upon the replication profile of the virus strain. Therefore, blood samples should be tested regularly after exposure: 2 weeks; 4 weeks; 6 weeks; 8 weeks; 10 weeks and 12 weeks. Samples should be tested for the presence of HIV proviral DNA in the peripheral blood lymphocytes by polymerase chain reaction, particularly Real-time PCR assay from an accredited laboratory. Looking for HIV RNA in plasma during window period is less sensitive. Samples collected after 6 weeks post-exposure should first be tested for the presence of HIV antibodies. If positive, it will indicate HIV infection.