Problems in the interpretation of HIV-1 viral load assays using commercialreagents

During routine monitoring of human immunodeficiency virus (HIV) viral load, two problems arose. First, a number of patients, the majority being Africa n, were found to have low viral loads by the Chiron branched-chain DNA assa y in conjunction with low CD4(+) cell numbers. In order to determine whethe r this was due to failure of the branched-chain DNA assay to detect non-B s ubtypes of HIV, selected samples were subtyped and HIV RNA quantified by br anched-chain DNA, NASBA, and the Roche Monitor RT-PCR assay. Twenty-eight ( 97%) of 29 Africans were infected with a non-B subtype of HIV and 15 (93.7% ) of 16 non-Africans with subtype B. Twenty-three samples had a low viral l oad by branched-chain DIVA, which was confirmed by the NASBA and RT-PCR ass ays. All three assays detected B and non-B subtypes with similar efficiency ; NASBA failed to detect HIV RNA in a small number of non-B samples. Discre pancies between viral load and CD4(+) cell numbers did not appear therefore to be related to subtype. Second, while quantification of HIV RNA was bein g conducted using Version 2 of the branched-chain DNA assay (lower detectio n limit 500 HIV RNA copies/ml) the manufacturers had developed a more sensi tive assay and a comparative evaluation was therefore conducted. In approxi mately 30% of samples the viral load was up to 10 times higher with the mor e sensitive assay. These experiences emphasise the importance of close coll aboration between the clinic and the laboratory. (C) 2000 Wiley-Liss, Inc.