Erythrocyte morphology in asymptomatic microhematuria: experimental studies and clinical significance

Renal and postrenal origin of hematuria can be differentiated by analysis of the morphology of the erythrocytes in the urinary sediment. In order to investigate the mechanisms which cause the membrane changes in dysmorphic erythrocytes, indicating renal origin of bleeding, normal red blood cells were exposed in vitro to an osmotic environment similar to that of the nephron. Upon exposure of osmotically challenged erythrocytes to a hemolytic environment, 50 to 90% of the cells became dysmorphic in a time- and dose-dependent manner and were indistinguishable on light and electron microscopy from those obtained in vivo from a patient with proven glomerular microhematuria. The reliability of erythrocyte morphology in differentiating between renal and postrenal microhematuria was evaluated by performing microscopic analysis as the initial step in the investigation of 316 consecutive patients. In 123 patients with eumorphic red cells in their urine complete urological investigation revealed a postrenal source of bleeding in 85%. Out of 193 patients with dysmorphic erythrocytes, 132 were followed up for at least 2 years after only minimal diagnostic evaluation. An additional postrenal source of bleeding developed in two patients, which was easily diagnosed by the change in erythrocyte morphology. Our studies, representing experience over 6 years with asymptomatic microhematuria, show that microscopic examination of erythrocyte morphology as initial diagnostic step is a safe, inexpensive and efficient method which renders invasive investigations superfluous in the majority of patients.