Calcium oxalate crystallization properties in urine with different specific electrical conductivities.

The relationship between the degree of urine dilution and the risk of calcium oxalate crystallization was studied in 32 urine samples collected from stone formers and normal subjects during an 8-hour period between 10 p.m. and 6 a.m., and in 4-hour urine samples collected during 24-hour periods from 6 patients with calcium stone disease. The risk of calcium oxalate crystallization was analyzed in terms of the increase in oxalate concentration required for a standardized precipitation of crystals of calcium oxalate. The degree of urine dilution was determined with a new instrument (urimho) designed for measuring the concentration, in terms of specific electrical conductivity, in urine samples of droplet size. With this device urine concentration can be expressed in urimho values between 1 and 5. There was a good correlation between recordings of specific electrical conductivity performed with the new device and with a conventional conductivity meter. There was a statistically significant positive correlation between urimho values and calcium oxalate crystallization. Calcium oxalate crystallization greater than 1.3 was not observed in any sample with a urimho value of 2 but it was noted in 31% of the samples with urimho values greater than 2. A positive relationship was also recorded between the urine pH and the urimho level, which is noteworthy because there was an inverse relationship between urine pH and calcium oxalate crystallization. A pH greater than 6 was observed in 78% of the samples with a urimho value of 2 but it was noted in only 27% of the samples with urimho readings between 3 and 5. A considerable variation in the response in urinary flow to ingested volumes was recorded. Therefore, monitoring of urine dilution by means of a sample device like the urimho might be of great help for patients with calcium stone disease in an effort to prevent recurrent stone formation by urine dilution, provided a urimho value of less than 3 can be maintained.