Urinary red cell size: diagnostic value and determinants.

Urinary red blood cells (RBC) are usually small and morphologically abnormal in glomerular (GN) hematuria, and slightly enlarged and morphologically normal in nonglomerular (NG) hematuria. This study was performed to evaluate the diagnostic value of urinary red cell size and morphology and to investigate the mechanism of the alteration in cell size. In 34 consecutive patients with hematuria we examined the urinary RBC size distribution and mean corpuscular volume (MCV) by electronic sizing of suspensions of RBC in an isotonic medium and, in 28 cases, compared it with the presence of 50% or greater dysmorphia. In 15 consecutive cases, we correlated MCV values with urine chemistries. In two GN cases we recorded the urine MCV serially during a furosemide-induced diuresis. In vitro incubations of peripheral or urinary RBC in various electrolyte solutions prior to sizing were also performed. The MCVs were significantly lower in GN (p less than 10(-6)) and probable GN (p less than 10(-4)) than NG hematuria. A cutoff of 72 fl completely separated GN and probable GN from NG cases. Fifty percent or more 'dysmorphic' RBC were seen in 12 of 13 GN, 3 of 4 probable GN but in no NG sediments. In patients with NG hematuria, the ratio of urinary to peripheral MCV tended to be greater than unity and correlated strongly with pH (r = -0.97; p less than 0.002). The effect of pH was confirmed in vitro. Furosemide diuresis induced a partial correction of the microcytosis of GN RBC, which correlated with the changes in urine composition. Furosemide had no effect on GN cells in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)