Experiences with the measurement of inhibitory activity of urine and crystallisation inhibitors by different techniques.

The effect of urine, pyrophosphate (PPi), citrate and diphosphonate on the formation, the growth rate or the aggregation of calcium oxalate or calcium phosphate crystals was measured by 4 different methods. The degree of supersaturation and the area of crystal surface present in the test systems were found to be limiting factors for the action of inhibitors. Citrate and PPi proved to be important urinary inhibitors of the growth of calcium oxalate crystals. Comparison between stone formers and healthy controls revealed a significant lack of PPi in urine of male patients. The inhibitory effect of PPi in urine of healthy people was enhanced by unknown factors. This enhancement could not be found in about 60% of the stone patients. Problems relating to measurement and clinical importance of inhibitors are discussed.