Osmotic resistance of urinary red cells in glomerular and non-glomerular haematuria

The determination of glomerular or non-glomerular origin of urinary red blood cells (U-RBC) is an important goal in the management of haematuric children. Morphological changes of glomerular RBC are secondary to cell membrane damage, due, in part, to the hypotonic osmotic stress to which U-RBC are submitted during their passage through tubular segments. This study was performed on 2 urine specimens obtained from 30 patients with a known cause of haematuria. After centrifugation, both sediments were resuspended in two saline solutions (at 200 mosm/l and at 300 mosm/l) where they remained for 90 min. The number of U-RBC per microliters in each (U-RBC 200 and U-RBC 300) was determined by microscopic count in Burker's chamber. The U-RBC 200/U-RBC 300 ratio was calculated for all patients. We found that in non-glomerular haematuria the ratio was near to 1, whereas cases of glomerular origin had lower values. The discriminant threshold between this ratio was 0.76 (p < 0.001). We suggest that determination of osmotic resistance of U-RBC may be a reliable method to differentiate the origin of bleeding in haematuric children.