Could the new HIV combined p24 antigen and antibody assays replace p24 antigen specific assays

The performance of twelve HIV combined p24 antigen and antibody assays available in Europe were compared. The assays were examined with a total of 1983 samples that included 1005 unselected HIV negative samples, 7 HIV-1 p24 Ag reference samples with HIV-1 Ag, 10 samples of a HIV antigen sensitivity commercial panel, 124 samples of 31 p24 antigen panels of different HIV-1 subtypes, 168 members of 24 HIV-1 seroconversion panels, 559 HIV-1 (groups M and O) antibody positive samples and 110 HIV-2 antibody positive samples. The specificity ranged from 99.4 to 100%. Ten of the 12 assays detected all anti-HIV positive samples irrespective of genotype while two assays missed one sample each (one subtype F and one subtype C). The combined assays could be classified into three groups. The first includes two assays (Enzygnost HIV Integral and Vironostika Ag/Ab) that have a clinical sensitivity similar to the two antibody only assays. The second includes the seven assays that detected infection after the p24 antigen only assay and show a delay from 3.3 to 5.17 days after HIV-1 RNA. The third group detected the infection before the p24 antigen assay and less than 3 days after nucleic acid testing (NAT). The improved ability to detect p24 Ag, at levels similar to specific HIV Ag assays, suggests that these new HIV combined Ag/Ab assays could replace p24 antigen only assays in situations for blood or organ screening when NAT is not feasible or not affordable.