CLINICAL COMPARISON OF AN ENHANCED-SENSITIVITY BRANCHED-DNA ASSAY ANDREVERSE TRANSCRIPTION-PCR FOR QUANTITATION OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 RNA IN PLASMA

The performance characteristics of an enhanced-sensitivity branched-DN A assay (bDNA) (Quantiplex HIV-1 version 2.0; Chiron Corp., Emeryville , Calif.) and a reverse transcription (RT)-PCR assay (AMPLICOR HIV-1 M onitor; Roche Diagnostic Systems, Inc., Branchburg, N.J.) were compare d in a molecular diagnostic laboratory. Samples used in this evaluatio n included linearity and reproducibility panels made by dilution of a human immunodeficiency virus type 1 (HIV-1) stock culture of known vir us particle count in HIV-1-negative plasma, a subtype panel consisting of HIV-1 subtypes A through F at a standardized level, and 64 baselin e plasma specimens from HIV-1-infected individuals. Plots of log(10) H IV RNA copies per milliliter versus log(10) nominal virus particles pe r milliliter demonstrated that both assays were linear over the stated dynamic ranges (bDNA, r = 0.98; RT.-CR, r = 0.99), but comparison of the slopes of the regression lines (bDNA, m = 0.96; RT-PCR, m = 0.83) suggested that RT-PCR had greater proportional systematic error. The b etween-run coefficients of variation for bDNA and RT-PCR were 24.3 and 34.3%, respectively, for a sample containing 1,650 nominal virus part icles/ml and 44.0 and 42.7%, respectively, for a sample containing 165 nominal virus particles/ml. Subtypes B, C, and D were quantitated wit h similar efficiencies by bDNA and RT-PCR; however, RT-PCR was less ef ficient in quantitating subtypes A, E, and F. One non-B subtype was re cognized in our clinical specimens based on the ratio of values obtain ed with the two methods. HIV-1 RNA was quantitated in 53 (83%) baselin e plasma specimens by bDNA and in 55 (86%) specimens by RT-PCR. RT-PCR values were consistently greater than bDNA values, with population me ans of 142,419 and 67,580 copies/ml, respectively (P < 0.01). The resu lts were highly correlated (r = 0.91), but the agreement was poor (mea n difference in log(10) copies per milliliter +/- 2 standard deviation s, 0.45 +/- 0.61) for the 50 clinical specimens that gave discrete val ues with both methods.