(A) Representative results of sensitivity of QAS-PCR detection of male donor WBCs in enriched subpopulations from spiked female blood. Four different male donor blood samples with known leukocyte concentrations were diluted fourfold, and serial dilutions were spiked into four different female recipient whole blood samples. For the assay of CD4⁺ cells, three different levels of male CD4⁺ cells (32, 8, and 2) were spiked into female blood, and for CD8⁺ cells, 27, 5, or 1 male CD8⁺ cells were spiked. For the CD15⁺ cell assay, 30, 6, or 1 male CD15⁺ cells were spiked, and for the CD19⁺ cell assay, samples containing 60, 12, or 2 male CD19⁺ cells were created. Each dilution was then processed through the assay protocol. (B) Representative results of QAS-PCR reproducibility (6×) for male donor CD4⁺ cells spiked into female whole blood.