Abstract
To examine the factors and patient characteristics predisposing to formation of calcium oxalate monohydrate or calcium oxalate dihydrate kidney stones, we compared blood and 24-hour urine tests, gender distribution and patient age in 2 groups of patients with pure calcium oxalate monohydrate (422) and calcium oxalate dihydrate (68) stones treated at the lithotripsy unit of the Wellesley Hospital and University of Toronto during 4 years. The calcium oxalate monohydrate group included relatively more women (31% versus 16% in the calcium oxalate dihydrate group, chi-square 7.89, p = 0.005). Patients were older in the calcium oxalate monohydrate group (59 ± 13 versus 51 ± 13 years, p = 0.001). The calcium oxalate monohydrate group had lower urinary calcium (4.19 ± 2.34 versus 7.19 ± 3.38mmol, per day, p <0.0001), calcium oxalate relative saturation rate (6.9 ± 3.9 versus 8.9 ± 3.3, p = 0.001), brushite relative saturation rate (0.7 ± 0.8 versus 1.2 ± 0.9, p = 0.0001) and urinary pH (5.72 ± 0.75 versus 5.93 ± 0.72). When corrected for patient age and gender, the calcium oxalate dihydrate group still had higher urine calcium levels. Higher urine pH in the calcium oxalate dihydrate group was age-related. In summary, we present evidence that calcium oxalate dihydrate stones are relatively more common among younger male patients with higher urine calcium levels and higher urine pH.
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