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Comparison of the Roche Amplicor HIV-1 Monitor Assay and the Roche COBAS TaqMan HIV-1 Assay for the Measurement of HIV in EDTA- and PPT-preserved Plasma Samples in South Africa
Zinhle Makatini*1, Z Hu2, D Follmann2, H Highbarger3, N Poole4, J Trusler4, P Sangweni5, J Metcalf2, H Lane2, and R Dewar3
1Univ of Limpopo, Pretoria, South Africa; 2NIAID, NIH, Bethesda, MD, US; 3SAIC-Frederick, MD, US; 4BARC SA Pty Ltd, Johannesburg, South Africa; and 5Project Phidisa, 1 Military Hosp, Pretoria, South Africa
Background: To determine the concordance between 2 methods for
measuring HIV viral load, we tested 452 plasma samples, half preserved with
EDTA and half preserved with Plasma Preparation Tubes (PPT), with the Roche
Amplicor HIV-1 Monitor assay and the Roche COBAS TaqMan
HIV-1 assay.
Methods: Duplicate plasma samples, one preserved with EDTA and the
other with PPT, from 126 patients enrolled in a prospective, randomized,
treatment protocol in South Africa (Project Phidisa), were tested using 2
commercially available assays for measuring HIV viral load: the Amplicor HIV-1 Monitor assay (Roche Diagnostics) and the
COBAS TaqMan HIV-1 assay (Roche Diagnostics). Results
were analyzed for concordance using the paired t-test, least squares regression, and box plot. Agreement between
measures was determined using the Bland-Altman difference regression.
Results: Analysis indicates that when measures above the limit of
detection are compared, Amplicor tends to produce viral load readings about 0.2
log10 higher than TaqMan for both EDTA and
PPT preserved samples. However, 1 unit of change in TaqMan
reading corresponds to roughly the same amount of change in Amplicor
reading. In addition, evaluation of
agreement between the measures indicates that the TaqMan
and Amplicor Monitor assays yield concordant results
(measurements differ <0.5 log10) for EDTA (82%) and PPT (81%)
samples.
Conclusions: Although the TaqMan assay
produces lower viral load readings than the Amplicor assay, this newer,
real-time polymerase chain reaction method of viral load measurement is an
acceptable alternative to the Amplicor assay for both EDTA and PPT preserved
samples, and shows trends in viral load as accurately as the Amplicor
assay. In addition, its wider linear
range (40 to 10,000,000 copies/mL, as opposed to the Amplicor’s 50 to 75,000 copies/mL) not only makes it a more
desirable tool for following patient progress on treatment protocols, but
eliminates the added time and cost required to dilute samples in order to
obtain a meaningful reading.
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