Comparison of quantitative and qualitative PCR assays for cytomegalovirus DNA in plasma

Abstract

We analyzed the performance characteristics of the qualitative AMPLICOR CMV Test (Roche Molecular Systems, Pleasanton, Calif.) and quantitative COBAS AMPLICOR CMV MONITOR Test (Roche Molecular Systems) assays and compared the performance of the AMPLICOR quantitative assay with an in-house-developed cytomegalovirus (CMV) DNA PCR assay. The quantitative AMPLICOR assay was found to be more sensitive than the qualitative AMPLICOR assay. The quantitative AMPLICOR assay has a lower limit of sensitivity of 400 CMV DNA copies/ml of plasma and is linear to 50,000 CMV DNA copies/ml of plasma. Compared to the in-house PCR assay, the AMPLICOR quantitative assay gave lower viral load values at all concentrations tested, but the difference between the two assays was not consistent across the entire dynamic range of the AMPLICOR quantitative assay. At the lower end of the assay, the viral load values obtained with the in-house PCR assay were three- to fivefold (0.5 to 0.7 log units) higher than those measured with the AMPLICOR assay. At higher input concentrations, the differences between the two assays approached 10-fold. This direct comparison of the in-house assay and the quantitative AMPLICOR assay provides the ability to compare previously published in-house data with an assay widely available for future research and clinical monitoring of patients with CMV infections.

FIG. 1

(A) Mean log₁₀ CMV DNA for each laboratory versus the input concentration of the quantitation standard (nominal CMV DNA scaled by +1 log₁₀ unit). The diagonal line indicates identity. Laboratories 1 to 3 used the quantitative AMPLICOR assay; laboratory 4 performed an in-house PCR assay. (b) Mean residuals (i.e., observed value minus expected value) for all three laboratories performing the quantitative AMPLICOR assay.

FIG. 2

The standard deviation of the log₁₀ CMV DNA copy number versus the input concentration of the quantitation standard (nominal CMV DNA scaled by +1 log₁₀ unit) for the three laboratories performing the quantitative AMPLICOR assay. The horizontal dotted line is at 0.15 log₁₀ unit.