FIG. 1.

Comparison of plasma viral load determination by using QIAamp extraction versus the standard Amplicor protocol. Aliquots of clinically obtained HIV-1-positive plasma specimens were thawed and measured by the standard Amplicor test. Other aliquots of these specimens were thawed, diluted 10-fold in HIV-negative control plasma, and extracted by the QIAamp procedure, and the purified RNA was measured by the Amplicor test. Expected viral loads were calculated as 10% of the value measured for the undiluted aliquot by the standard Amplicor test. Closed squares, data points for specimens with a detectable measurement in the QIAamp test. One diluted specimen (open square) was negative for HIV RNA (expected readout, 73 copies/ml; measured value, <17 copies/ml). Linear regression (r² = 0.91; n = 22), as shown by the solid line, and the 95% confidence intervals (dotted lines) result in an equation of y = (0.97 ± 0.07)x − (0.14 ± 0.18) (the slope and the y-intercept values are indicated as the mean ± SE).