Diagnostic impact of dysmorphic red blood cells on evaluating microscopic hematuria: the urologist’s perspective

Purpose: Dysmorphic red blood cells (dRBCs) are indicative of glomerular disease and considered a first step in evaluating microscopic hematuria (MH). The predominance of dRBCs does not preclude urological disease; however, some contemporary guidelines advise nephrological evaluation without further urological evaluation, in contrast to the American Urological Association guideline. We investigated the feasibility and safety of omitting urological evaluation in patients presenting with MH. Methods: A retrospective analysis was performed on 411 consecutive patients who presented with MH between January 2012 and December 2014. MH was defined as ≥3 RBCs per high-power field. All patients received full urological and nephrological evaluations including history and physical assessment, renal function, urine cytology, %dRBC, cystoscopy, computed tomography (CT) imaging, and renal biopsy when indicated. Results: The median %dRBC was higher in patients with glomerular disease than in those with urological disease (40.4 vs. 21.1 %; p < 0.001). Among patients exhibiting %dRBC ≥ 40, 33/97 (34.0 %) had urological and 28/97 (28.9 %) had glomerular diseases. Urological diseases included 9/33 (27.3 %) clinically meaningful malignancies and 17/33 (51.5 %) conditions requiring immediate treatment. The rate of malignancy was comparable between %dRBC groups (p = 0.087). Among patients with final diagnoses who exhibited %dRBC ≥ 40, 32/61 (52.5 %) treatment-requiring conditions would have been unrecognized had cystoscopy and/or CT not been performed. For predicting glomerular disease, the presence of proteinuria demonstrated higher AUC than %dRBC ≥ 40 (0.77 vs. 0.65; p < 0.001). Conclusions: Identification of %dRBC ≥ 40 had modest diagnostic value in identifying glomerular disease, and concomitant presence of proteinuria was more indicative of glomerular origin in patients presenting with MH. Urological evaluation should not be omitted in these patients considering the prevalence of treatment-requiring urological disease.