Proportion of patients and controls with BK viremia. (A) The proportion of patients among controls and cases in each subset of HC who developed BK viremia at any level before or during HC. Post-eng indicates postengraftment. (B) The proportion of patients among controls and cases in each subset of HC who developed BK viremia above 10⁴ copies/mL. The sensitivity and the specificity of PCR-based BK viremia at any level either before or at time of HC was 86% and 75%, respectively, for clinical HC, and 92% and 72%, respectively, for postengraftment HC with documented BK viruria. The sensitivity and the specificity of BK viremia before HC was 66% and 85%, respectively, for clinical HC, and 92% and 88%, respectively, for postengraftment HC with documented BK viruria. Plasma BK viral load that measured above 10⁴ copies/mL before or during HC had a sensitivity and specificity of 63% and 95%, respectively, for diagnosing HC; and 57% and 95%, respectively, for diagnosing postengraftment HC with documented BK viruria.