Eosinophiluria is common among patients after ileal conduit surgery

Background: Urinary eosinophils are used to screen for acute interstitial nephritis (AIN). Technologists in the Mayo Clinic Renal Laboratory observed that patients with urinary diversion surgeries frequently had an unusually high number of urinary eosinophils. Methods: Urine samples from three cohorts of patients were studied (n=20 each): (1) urinalysis samples with a "stoma" source indicating a previous ileal conduit surgery; (2) urine samples clinically submitted for eosinophil quantification; (3) randomly selected urinalysis samples with a minimum of 1-3 white cells per high-powered field. Urinary eosinophils were quantified after Hansel staining as the mean of independent counts by four blinded technologists. Results: Eosinophils composed an average 19% of the urinary white cells in the stoma group, even though none had a clinical suspicion of AIN. In contrast, only 3.5% and 4.6% of the urinary white cells were eosinophils among patients with clinically-ordered eosinophiluria testing and in a random sample of patients with pyuria, respectively (p<0.001 for each group vs. the stoma patients). Importantly, 90% (18 out of 20) of the stoma patients had >5% eosinophils, meeting the criterion for a positive test. Conclusions: Patients with a previous ileal conduit surgery have markedly elevated urinary eosinophils, far in excess of typical patients with pyuria or those with clinically-ordered eosinophiluria testing. Therefore, urinary eosinophils are not a useful screen for AIN in patients after ileal conduit surgery.