THE VALUE OF COMPARATIVE VOLUMETRIC ANALYSIS OF URINARY AND BLOOD ERYTHROCYTES TO LOCALIZE THE SOURCE OF HEMATURIA

Abstract

Purpose We evaluate comparative volumetric analysis of blood and urinary red blood cells (RBCs) to identify the source of hematuria. Comparative volumetric analysis is defined as the difference between mean corpuscular erythrocyte volume in peripheral blood (MCVB) diluted in urine supernatant after centrifugation and mean corpuscular volume of urinary erythrocytes (MCVU). The potential of MCVB-MCVU to distinguish the origin of hematuria is compared to MCVU alone. The fundamental hypothesis is that RBCs that can go through the glomerulus will be smaller than those from the collecting system or lower urinary tract, thus having a smaller MCVU and larger difference between MCVB and MCVU. Materials and Methods A prospective detailed urological evaluation was performed on 210 patients with glomerular or nonglomerular hematuria detected by urinary sediment, clinical radiological evaluation, endoscopy, cytology, and sometimes bladder or renal biopsy. After evaluation 24 cases with an uncertain source of hematuria were excluded from study. Specialized urinalysis, volumetric analysis and clinical investigation were performed in a blind fashion. MCVU and MCVB-MCVU were registered for every patient. The Technicon* H-3 system with angle laser scattering dual system allowed measurement of mean corpuscular volume in a minimal number of RBCs, and resuspension of RBC pellets in the same urinary supinate avoided effects of osmolarity and pH on RBC size and shape. Reproducibility in assessing the index was tested in 50 cases in which comparative volumetric analysis was repeated on 2 consecutive days. Unpaired t test was performed, and a threshold value of MCVB-MCVU with maximum sensitivity and specificity to detect glomerular hematuria was identified. The potential of urinary and comparative volumetric analysis to distinguish the source of hematuria was evaluated and compared by receiver operating characteristics curve analysis. Results Hematuria was nonglomerular in 53 (28.4%) and glomerular in 133 (71.6%) patients. Mean MCVB-MCVU was significantly different for nonglomerular (0.6 fl.) and glomerular (30.5 fl.) sources (p < 0.0001). There was a correlation between repeat independent measures of MCVU and MCVB-MCVU. The highest positive predictive value to detect a glomerular origin is desirable so that unnecessary investigation can be obviated without the risk of missing a nonglomerular source. With a limit of 16 fl. specificity and positive predictive value were 98 and 99%, respectively. Receiver operating characteristics curve analysis to localize the source of hematuria revealed significant differences in favor of comparative volumetric analysis versus urinary volumetric analysis alone. Conclusions MCVB-MCVU using the Technicon H-3 system is a useful noninvasive and accurate method to locate the source of hematuria. A value of 16 fl. or greater practically rules out a nonglomerular origin and obviates further urological investigation. We have incorporated this investigation in our diagnostic algorithm for hematuria.