QUANTIFICATION OF HIV-1 RNA IN PLASMA - COMPARABLE RESULTS WITH THE NASBA HIV-1 RNA QT AND THE AMPLICOR HIV MONITOR TEST

We investigated and compared the reproducibility, accuracy, detection limits, and dynamic ranges of two commercial kits for quantification o f RNA viral load using a titrated virus stock (laboratory strain HIV-1 IIIB) and 107 plasma samples of 25 HIV-1-infected patients. The high reproducibility of both methods (SD = 0.2-0.3 log for both methods) al lowed reliable detection of a 0.5 log change in RNA viral load. Both m ethods had a similar detection limit (at least 10(3) RNA copies/ml pla sma) and a dynamic range that extended over a 5 log (AMPLICOR) or a 6 log (NASBA) range of HIV-1 input. For HIV-1 IIIB, the viral load was c ompatible with measurements of virus-associated p24 antigen. For 21 pa tients (91 samples), the RNA viral load was similar with both methods, differing by no more than 0.5 log. For four patients, the difference in viral load between the two methods was >0.5 log for all 16 samples. For three of these patients, this could be explained by mismatches wi th primers or probes in the gag sequence; there was no correlation to the viral subtype. The RNA viral load determination was highly sensiti ve compared with p24 antigen measurement (>95% of patients had a detec table viral load vs. 40% who had a detectable p24 level), but in the p 24-positive samples the correlation between the antigen level and the RNA viral load was of only borderline significance. We also found that the viral RNA in whole blood was stable for at least 48 h during tran sport at room temperature. These observations show that both the NASBA HIV-1 RNA QT test and the AMPLICOR HIV monitor test are reliable para meters of the viral load, with great promise for their use as potentia l surrogate markers.