6H 4 2-| 0 Dear Sir, Docci et al. [1] reported recently that urinary red cell volume distribution curves (RCVDC) obtained using red cell analysers (RCA) were useful in diagnosing glomerular and nonglomerular haematuria. In an evaluation of the technique in patients with haematuria referred to a hospital-based nephrourology unit we found the technique lacked specificity and sought reasons to explain this. We used a Coulter S + IV RCA and a modification of the method of Shichiri et al. [2] to

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... are the samples. 10 ml of fresh urine was centrifuged (1,500 rpm, 5 min), the supernatant removed and the sediment resuspended in Isoton III buffer and injected directly into the red cell counting chamber. Urine was passed through polycarbonate filters (0.8 and 3.0 µm, Nucleopore) and these examined with scanning electron microscopy. Centrifuga-tion of urine against a sucrose polymer was used in an attempt to separate urinary RBC from urinary debris. The serial dilution of normal peripheral blood in urine produced in turn, non-glomerular, mixed and glomerular RCVDC at decreasing cell concentrations. In addition, urine from 7 normal subjects (6 without urinary RBC and 1 with 35 × 10V1) all showed glomerular RCVDC. Filtration of haematuric urine from a 79-year-old man after prostatectomy (fig. la) trapped RBC (3.5-9.5 µm diameter) and particulate debris (1.0-7.5 µm diameter). Urine from a 56-year-old man with crescentic glomerulonephri-tis (fig. lb) produced similar results although it was not possible to carry out an estimate of red cell size (particulate debris 1-13 µm diameter). RCVDC from the cells obtained following centrifugation of urine against the sucrose polymer showed modal cell volumes < 50 fl or 80-100 fl, i.e. RCVDC thought to indicate glomerular or 0 12 3 4 Diameter, µm 9 10 11 12 13 14 15 16 Fig.l . Size distribution of urinary particles obtained by filtration of haematuric urine from a 79year-old man after prostatectomy (a) and a 56-year-old man with crescentic glomerulonephritis (b). ¾ = RBC. non-glomerular haematuria. Direct microscopy showed predominantly cellular debris with the RBC pellet and predominantly amorphous debris at the supernatant/ sucrose junction.