Validation of Post-Acidification p24 Antigen as a Prognostic Marker for HIV Disease Progression

The HIV p24 antigen has demonstrated predictive value for HIV disease progression independent of CD4 count. An acidification procedure has resulted in 40–70 percent p24 antigen positivity across HIV clinical stages, although the predictive value of post-acidification p24 antigen for disease progression has not been fully validated. We hypothesized that there would be significant differences in p24 antigen positivity between matched cohorts of rapid progressors (RP) and slow progressors (SP). Seven hundred sixteen people enrolled in the USAF HIV Natural History Study were stratified according to the slope of CD4 change over time. RP were defined as people in the fastest 15 percent of CD4 decline who also progressed at least 2 Walter Reed (WR) stages. SP were defined as people in the slowest 15 percent of CD4 decline who did not progress more than 1 WR stage. Twenty-five RP were matched to 25 SP based on initial CD4 count (median CD4 RP=750, SP=720), WR stage, age, and duration of follow-up (RP=1086 das, SP=1126 days) with no significant differences between groups. Ten/25(40 percent) of the RP and 2/25(8 percent) of the SP were p24 antigen positive by the acidification assay (p=0.018). Using the standard assay, 6/25(24 percent) of RP and 1/25(4 percent) of SP were p24 antigen positive RP and SP. p24 antigen as detected with the acidification assay was predictive ffor HIV rapid progressors when compared to slow progressors in early stage HIV patients even when controllong for initial CD4 count, age, and duration of follow-up.