Calcium oxalate crystalluria: crystal size in urine.

Studies of calcium oxalate crystals in urine suggest similarities to crystal growth in calcium oxalate renal calculi. Previous reports indicate that urinary crystals in patients in whom stones form are larger than those in normal subjects. We report herein a study on crystal size by structure and habit (shape) based on direct microscopic measurement of crystals in urine of 27 normal subjects and in 6 of 22 patients in whom stones form. The mean size of all crystals in normal subjects is 12.0 plus or minus 7.8 micrometers. Calcium oxalate monohydrate crystals are significantly smaller than calcium oxalate dihydrate (p less than 0.01). In 22 patients with stones there was no correlation between crystalluria and severity or duration of disease. The mean crystal size in 6 patients did not support the conclusion that patients in whom stones form excrete larger crystals than normal subjects.