Differential diagnosis of acute allograft rejection and CMV-infection in renal transplantation by urinary cytology.

Acute allograft rejection and CMV-infection are the most common complications after renal transplantation. Quick differential diagnosis between these two complications is still difficult but necessary, since both complications demand a different therapy. More than 2500 urinary samples from 33 transplanted patients were prospectively examined and part of them evaluated quantitatively. Urinary samples of patients with acute renal failure, long-term haemodialysis or immunosuppressive therapy served as controls. The following cytomorphological criteria proved to be useful: Tubular epithelial cells, casts, oxalate crystals (sand-glass shaped), dirty background, increasing erythrocyturia, mixed cell clusters, lymphocytes and mitoses. Rejection is going on when the number of renal tubular cells is increased and two or more further criteria are positive. 25 acute allograft rejections without acute renal failure were diagnosed clinically. All 25 rejections were also diagnosed by urinary cytology. Nevertheless, it is not possible to differentiate between acute allograft rejection and acute renal failure of other origin. CMV-infection was serologically detected in 7 patients. In 6 of them viral infected cells were found in the urine shortly after the onset of unspecific clinical symptoms. Besides the typical "owl-eye" cells milkglass nuclei, sometimes with eosinophilic condensation, were seen while criteria for transplant rejection were never observed at the same time. Cytologic examination of voided urine is a simple diagnostic help for the differentiation between allograft rejection and CMV-infection after renal transplantation.