Correction of under-quantified specimens with the second version of the Roche COBAS(R) AmpliPrep(R)/COBAS(R) TaqMan(R) assay for HIV-1 viral load

Initial evaluations of the COBAS(R) AmpliPrep/COBAS(R) TaqMan(R) HIV-1 Test (CAP/CTM) showed good performance but afterwards reports about under-quantification became available. The aim of this study was to investigate if the problem is solved with the second version of this assay, the COBAS(R) AmpliPrep/COBAS(R) TaqMan(R) HIV-1 Test, version 2.0 (CAP/CTM v2.0). Remaining plasma of 375 consecutive HIV-1 positive samples with viral load >/=4000 copies/ml was collected in 3 labs. Samples were diluted and retested with our routine method COBAS(R) AmpliPrep/COBAS(R) AMPLICOR(R) HIV-1 MONITOR Test v1.5 in the ultrasensitive mode (CAP/CA PHS) as well as with CAP/CTM and CAP/CTM v2.0 tests. An absolute difference between the results of two methods of >/=0.71 log10 copies/ml (cp/ml) was defined as moderately discrepant and an absolute difference of >/=0.93 log10 cp/ml as severely discrepant. In addition, criteria for considering the new methods equivalent to the routine method were formulated. CAP/CTM compared to CAP/CA PHS: 36 (9.5%) and 20 (5.3%) samples were respectively considered as moderately and severely under-quantified by CAP/CTM. The mean difference between CAP/CTM and CAP/CA PHS was -0.32 log10 cp/ml. Eight out of 19 of the severely under-quantified samples were from patients infected with HIV-1 subtype B strain. CAP/CTM v2.0 compared to CAP/CA PHS: No sample was moderately or severely under-quantified by CAP/CTM v2.0. A mean difference of +0.08 log10 cp/ml was found with CAP/CTM v2.0 compared to CAP/CA PHS. The under-quantification problem of the CAP/CTM kit was clearly demonstrated. Criteria for equivalence of CAP/CTM v2.0 to the routine test CAP/CA PHS were fulfilled.