EVALUATION OF A SIMPLE TEST TO ESTIMATE URINE SATURATION WITH CALCIUM OXALATE IN STONE-FORMING PATIENTS

Abstract

In 43 patients with recent-onset calcium oxalate nephrolithiasis (25 male, 18 female; age range: 17-61 yr), urine saturation with calcium oxalate (CaOx) was calculated using a computer program (Equil-AT). The results in kJ/mol (normal < or = 2.0) were compared with those obtained with a simple test consisting of the addition of increasing amounts of calcium and oxalate to 3 tubes containing 10 ml urine. Development of turbidity in tube I denotes urine supersaturation with CaOx; turbidity in tubes II or III indicates lesser degrees of saturation, while a lack of turbidity (NT: no turbidity) shows undersaturation. Both saturation estimates were performed using aliquots of 24-hour urine collections. Twenty-one samples developed turbidity in tube I, 9 in tube II, and 6 in tube III, while 7 showed NT. There were no significant differences in Equil-AT values between II and III and between III and NT (p < 0.05 for I vs II and I vs III). High computer-calculated saturation values were found in 86% of group I samples and 22% of group II samples. None of the urines exhibiting turbidity in tube III or NT had high saturation values as estimated by Equil-AT. The turbidity test was also performed using freshly voided morning urine samples from the same patients. The results agreed with those obtained using the same test on aliquots of 24-hour collections, although in 10.8% of patients the morning test indicated higher levels of saturation. It is concluded that the turbidity test is a rapid, inexpensive and accurate way of estimating urine saturation with CaOx in the outpatient clinic.