Correlation and agreement between assay-derived data and expected values.

aEach laboratory's assay-derived data were plotted against the expected values, and the slope (Δ assay-derived value/Δ expected value) and coefficient of determination (r2) were calculated using Microsoft Excel. A slope of 1.0 and r2 value of 1.0 indicates perfect correlation.bBland-Altman difference plots were used to calculate the mean quantitative bias as the mean of the differences between each reported value and its expected value. Values are in log10 parasites/mL. An absolute value of ≤0.5 log10 parasites/mL indicates an absence of quantitative bias.cAll calculations were based on all NAT-positive samples.dNIH quantities were generated by regression of CT values to nominal values and should be viewed as a measure of variation only.