Red cell volume distribution curves in the diagnosis of glomerular and non-glomerular hematuria

It has been suggested that measurement of red blood cell (RBC) volume, by red cell analyzers (RCA), may be used to distinguish glomerular from non-glomerular hematuria. The RCA measures all urinary particles, including RBC. We found that red cell volume distribution curves (RVDC) obtained with a Coulter S+IV RCA were non-specific in predicting the cause of hematuria. Normal RBC added to urine at about 15,000/mm3 produced the expected non-glomerular RCVDC but at decreasing RBC concentrations mixed and then glomerular RCVDCs were found. Urine from 7 normal subjects (6 without urinary RBC) showed particle volume distribution curves identical to glomerular RCVDC. These urinary particles were examined by scanning electron microscopy (SEM) after filtration (3 microns and 0.8 micron pore size). Hematuric urine from a patient after prostatectomy contained RBC (3.5-9.5 microns diameter) and particulate debris (1.0-7.5 microns diameter). Similar results were obtained for a patient with crescentic glomerulonephritis (particles 1-13 microns diameter). Attempts to separate glomerular urinary RBC from debris by centrifugation against a sucrose polymer were unsuccessful. The shape of the RCVDC obtained with RCA is altered by the presence of debris in urine. The true MCV of glomerular RBC is still unknown. The usefulness of RCA in the diagnosis of hematuria is limited to patients with large numbers of urinary RBC.