[Erythrocytes in the urine: glomerulonephritis or other source of bleeding. Answer with the microscope].

On the basis of an evaluation of the morphology of erythrocytes in urinary sediment, it is possible to distinguish between nephrological and urological hematuria. In the case of the former, the cells have "disruptive characteristics" (membrane evagination, ring formations, dwarf forms and loss of hemoglobin), enabling them to be distinguished from the regularly formed erythrocytes from hemorrhage within the urinary tract. Dysmorphic erythrocytes retain their characteristic shapes even when persisting in the urine for lengthy periods. An assessment of erythrocyte morphology forms a suitable basis for choosing appropriate further diagnostic measures for urological or nephrological work-up. The method of examination is simple and readily reproducible, and should therefore form an early part of the diagnostic strategy. Microscopic assessment erythrocyte shape is not suitable for the diagnostic work-up of tumors, nor can it obviate the need for kidney biopsy for the investigation of histomorphological changes in glomerular nephritis.