New Method for Discriminating between Calcium Stone Formers and Healthy Individuals

Summary— A new method for discriminating between the urine of potential calcium stone formers and healthy persons has been proposed, based on determination of the calcium binding capacity of urine (CBC) by titration of early morning urine with a calcium chloride solution. For this purpose a new PVC matrix calcium ion selectrode for measuring calcium ion concentration in whole urine was used. The selectrode has a disposable membrane which can easily be prepared and replaced in the laboratory. Plots of the calcium ion concentration versus the concentration of total added calcium were linear up to a point where precipitation of calcium salts commenced. The slopes of these titration lines were used as criteria for discrimination. Statistical evaluation showed good separation between the urine of healthy and stone forming donors. A 2-sample t test with unequal variances gave mean values of 0.31 for healthy urine (13 samples) and 0.64 for stone forming urine (26 samples). Individual 99% confidence intervals were 0.21-0.40 for the controls and 0.54-0.73 for the patients respectively. D iscriminant analysis showed that from a group of treated patients with low DI (13 samples), 3 were classified as stone formers and 10 were non-formers. Thus there was good correlation with the clinical situation and with the previously proposed DI test.