HCV RNA serum concn (in IU/ml) Estimated input (in IU) of HCV RNAb No. positive/no. tested % Positive results 604,000 33,250 8/8 100 120,800 6,640 8/8 100 24,160 1,328 8/8 100 4,830 265 6/7 85.7 960 53 6/8 75 190 10.6 0/8 0 38 2.1 0/8 0 0 0 0/8 0

^a Uncoagulated blood from a viremic patient (viral burden, 604,000 IU/ml) was diluted with fresh blood from an HCV-seronegative individual. Eight five-fold serial blood dilutions were spotted to form multiple replicate DBS that were extracted and assayed as described in the text.

^b Estimated HCV RNA input in the DBS was determined by adjusting values for viremia in serum for the volume of blood spotted and for the relative hematocrit value.

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