A patient comes to hospital with a history of sore throat, diarrhea and sexual contact 2 weeks before. The best investigation to rule out HIV is -

The p24 antigen can be detected during window period, during which antibodies are not demonstrated in the serum. So, used for early detection. The p24 antigen appears within 2 weeks (average 16 days) after infection. So, it is the best investigation to rule out HIV among the options given above. Note: Nucleic acid test (NAT) is the earliest test to become positive, (even before p-24 antigen detection) Test Average period after infection when test becomes positive Nucleic acid test p24 antigen test Antibodies test 12 days 16 days 22 days Western blot: It detects the HIV antibodies. A lymph node biopsy can confirm a diagnosis of AIDS-related lymphoma.