Urine immunocytology as a noninvasive diagnostic tool for acute kidney rejection: a single center experience.

Renal biopsy is a gold standard for establishing diagnosis of acute rejection of the renal allograft. However, being invasive, renal biopsy has potential significant complications and contraindications. Therefore, possibility to noninvasively diagnose acute rejection would improve follow-up of kidney transplant patients. The purpose of this study was to evaluate urine immunocytology for T cells as a method for noninvasive identification of patients with acute renal allograft rejection in comparison to renal biopsy. In this prospective study a cohort of 56 kidney, or kidney-pancreas transplant recipients was included. Patients either received their transplant at the University Hospital "Merkur", or have been followed at the "Merkur" Hospital. Patients were subject to either protocol or indication kidney biopsy (a total of 70 biopsies), with simultaneous urine immunocytology (determination of CD3-positive cells in the urine sediment). Acute rejection was diagnosed in 24 biopsies. 23 episodes were T-cell mediated (6 grade IA, 5 grade IB, 1 grade IIA, 1 grade III and 10 borderline), while in 1 case acute humoral rejection was diagnosed. 46 biopsies did not demonstrate acute rejection. CD3-positive cells were found in 21% of cases with acute rejection and in 13% of cases without rejection (n.s.). A finding of CD3-positive cells in urine had a sensitivity of 21% and specificity of 87% for acute rejection (including borderline), with positive predictive value of 45% and negative predictive value of 68%. Although tubulitis is a hallmark of acute T cell-mediated rejection, detection of T cells in urine sediment was insufficiently sensitive and insufficiently specific for diagnosing acute rejection in our cohort of kidney transplant recipients.