Predictive Value of the Combination of Peripheral Blood Lymphocyte Count and Urinary Cytology in BK Polyomavirus–associated Nephropathy

Background: Graft biopsy is the gold standard for diagnosis of BK polyomavirus–associated nephropathy (BKPyVAN), and polymerase chain reaction is the most specific screening technique. Development of a noninvasive, cost-effective marker for BKPyVAN is important. Methods: We reviewed 492 adult kidney transplant patients. We investigated peripheral blood lymphocyte (PBL)count and urinary cytology at graft biopsy in patients with BKVPyAN (n = 21), acute T-cell–mediated rejection (n = 79), and no evidence of acute rejection (n = 149). We performed univariate and multivariate logistic regression and receiver operating characteristics analyses to compare the test performance of PBL count, urinary cytology, and their combination for diagnosis of BKPyVAN. Results: The PBL count at biopsy was significantly lower in the BKPyVAN group than the acute T-cell–mediated rejection and no acute rejection groups (959 ± 290/μL, 1433 ± 673/μL, and 1531 ± 549/μL, respectively; P <.01). The PBL count was 959 ± 290/μL at diagnosis of BKPyVAN and increased to 1123 ± 377/μL, 1238 ± 419/μL, and 1292 ± 491/μL at 1, 2, and 3 months after treatment, respectively (P <.05). On univariate analysis, the area under the curve was significantly higher for the combined model than for PBL and cytology alone (0.930, 0.797, and 0.875, respectively; P <.01). The improved test performance in the combined model remained significant after multivariate adjustment (0.972, 0.844, and 0.928, respectively; P <.01). Conclusions: Decreased PBL count was found in BKPyVAN, and the predictive performance of the combination of PBL count and urinary cytology was significantly enhanced for diagnosis of BKPyVAN.