Challenging Issues in Diagnosis and Screening of BK Virus Nephropathy in Kidney Transplant Recipients, A Multicenter...

BK virus nephropathy (BKVN) is an important complication of kidney transplantation and kidney biopsy remains the gold standard for its diagnosis. Urine/serum polymerase chain reaction (PCR) is a more sensitive diagnostic method, although it has some potential limitations.

This study enrolled all kidney transplant recipients who underwent kidney transplant biopsy, collected from three medical centers. Urine and serum PCR results of the patients were also collected from the molecular laboratories. The cut-off value for positive viral DNA load in serum and urine were > 104 and > 107 copies/mL, respectively. Sensitivity, specifity, positive and negative predictive values (PPV, NPV) and cut off values for PCR results were compared with pathologic diagnosis among laboratories.

Among 369 biopsy samples, 33 (8.9%) had definite diagnosis of BKVN. PCR results were available for 138 cases. Three patients with definite BKVN had negative PCR results. In 22 patients, PCR was positive without evidence of BKVN. The overall sensitivity, specificity, PPV and NPV of PCR for detecting BKVN, based on a unique cut-off value, were 88, 81, 51, and 97%; respectively. The overall accuracy of PCR in all laboratories was high (82 to 86%), however significant inter-laboratory differences in sensitivity and specificity was found . A 2-log difference in threshold value for positive results was observed in one laboratory.

PCR may show a significant variability between different laboratories. Interpretation of PCR results using a single cut-off value for all laboratories, may decrease the sensitivity for the diagnosis and screening of BKVN.