Low specific gravity urine with crystalluria as discriminant index for nephrolithiasis

A community-based study for crystalluria in morning urine (MU) specimens was carried out under light microscopy. The MU specimens were collected from 29 males with renal stones (GI), 36 age-and sex-matched normal controls (GII) and 27 household members of GI who did not have stones (GIII). The findings can be summarized as follows. 1. In the groups as a whole, almost all crystal and crystal aggregate found was oxalate type and with highest prevalence in GI. 2. In urine with low specific gravity (SG) i.e. less than or equal to 0.010, prevalence of oxalate crystals in GI (57.7%) was significantly higher (p less than 0.05) than in both GII (5.9%) and GIII (13%). Furthermore, at this range of SG, 15 per cent of the MU specimens in GI showed aggregation of oxalate crystals, whereas, the condition was neither found in GII nor GIII. 3. Our data suggest urine supersaturation with respect to calcium oxalate was found in both renal stone patients and normal subjects but more frequently in the former and also suggests more deficiency or lack of inhibitors for oxalate crystal nucleation and aggregation in urine of renal stone patients. The occurrence of oxalate crystals and crystal aggregates in urine of low SG may be useful as an index to discriminate stone patients from normal subjects or as an index to indicate the high risk group in the community.