Antiretroviral treatment monitoring with an improved HIV-1 p24 antigen test: An inexpensive alternative to tests for viral RNA

Monitoring of viral RNA has become indispensable for the management of HIV- 1 infection, but is expensive. This study investigated whether a highly imp roved test for p24 antigen could serve as an alternative. Thirty-four patie nts enrolled during 1997 into two treatment studies were tested prospective ly for viral RNA by the Roche HIV-1 Monitor((R)) and for p24 antigen using signal-amplification-boosted ELISA of heat-denatured plasma. P24 antigen wa s detectable in 75.8% of 178 samples and HIV RNA in 73.9% of 138 samples. T he half-life of p24 antigen in the first phase of effective treatment was 1 .6.4 days (RNA, 1.7 +/- .8). An apparent second, slower decay phase had a h alf-life of 42 +/- 16 days. Treatment failure occurred in 14 patients. Seco ndary treatment failures with RNA rebounds from undetectable levels to less than or equal to 10(3) copies/ml in two patients with an undetectable vira l load and 10(3) HIV RNA copies/ml, respectively, at baseline were not dete cted by p24 antigen but carried a low risk for secondary resistance mutatio ns. The other 12 failures were on average detected 29 days earlier by p24 a ntigen than by RNA (P=.0204), owing to slightly more frequent testing for p 24 than for RNA (2.7 vs. 2.4 tests). Average costs for p24 antigen testing up to a failure were only 20.5% of those for RNA (P < .0001). These results indicate that heat-denatured, amplification-boosted p24 antigen measuremen t can be used as a simple and inexpensive alternative to HIV RNA testing fo r monitoring treatment. (C) 2001 Wiley-Liss,inc.