Urine cytology and the diagnosis of renal allograft rejection: I. Studies using conventional staining

OBJECTIVE: To determine the reproducibility and validity of urine cytology for the diagnosis of acute renal allograft rejection (AR). STUDY DESIGN: We conducted a blind, prospective study of 10 renal allograft recipients. Freshly voided aliquots of urine were obtained on each hospital day and at each outpatient visit for a mean of 52.8 ± 26.2 (SD) days following transplantation. The samples were prepared by cytocentrifugation and then stained by a modified Papanicolaou method. To determine interobserver reproducibility, the differential cell counts of two blinded cytopathologists were compared. A cytodiagnosis of AR was made when the urine sample contained < 55% neutrophils and > 20% lymphocytes. To determine the validity of the cytology the result was compared to the histologic and clinical diagnoses. Biopsies were obtained one hour following vascular anastomosis and at the time of graft dysfunction and were scored by two blinded pathologists according to the Banff classification. The clinical diagnosis was determined by a retrospective review conducted by four blinded clinicians. RESULTS: The interoperator reading of urine cytology was more reproducible than histology, with kappa values of 0.40 ± 0.15 (SE) and 0.21 ±0.10 (SE), respectively. Urine cytology was accurate for the diagnosis of AR, with a sensitivity of 80% and a specificity of 96% as compared to the clinical and histologic findings. CONCLUSION: Our observations support the claim that urine cytology is useful for diagnosing AR.