Problems in the interpretation of HIV-1 viral load assays using commercial reagents.
During routine monitoring of human immunodeficiency virus (HIV) viral load, two problems arose. First, a number of patients, the majority being African, were found to have low viral loads by the Chiron branched-chain DNA assay in conjunction with low CD4(+) cell numbers. In order to determine whether this was due to failure of the branched-chain DNA assay to detect non-B subtypes of HIV, selected samples were subtyped and HIV RNA quantified by branched-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 load by branched-chain DNA, which was confirmed by the NASBA and RT-PCR assays. 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. Discrepancies between viral load and CD4(+) cell numbers did not appear therefore to be related to subtype. Second, while quantification of HIV RNA was being conducted using version 2 of the branched-chain DNA assay (lower detection limit 500 HIV RNA copies/ml) the manufacturers had developed a more sensitive assay and a comparative evaluation was therefore conducted. In approximately 30% of samples the viral load was up to 10 times higher with the more sensitive assay. These experiences emphasise the importance of close collaboration between the clinic and the laboratory.
O'Shea
S
S
Department of Virology, Guy's and St. Thomas' Hospital Trust, London, United Kingdom. o'shea@gstt.sthames.nhs.uk
Chrystie
I
I
Cranston
R
R
Mullen
J
J
Corbett
K
K
Murphy
G
G
Parry
J V
JV
De Ruiter
A
A
Banatvala
J
J
D018791:CD4 Lymphocyte Count; D005069:Evaluation Studies as Topic; D015658:HIV Infections / Q000097:blood / Q000276:immunology / Q000821:virology*; D015497:HIV-1 / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D006801:Humans; D012367:RNA, Viral / Q000097:blood; D011933:Reagent Kits, Diagnostic; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012703:Serotyping; D019562:Viral Load / Q000379:methods*
D012367:RNA, Viral; D011933:Reagent Kits, Diagnostic