A thermodynamic equilibrium model for calcium salt urolithiasis: clinical application.

It is proposed that urine is better modelled as a true equilibrium rather than in a supersaturated/metastable state and that the free citrate3- ion plays a major role in maintaining dispersion of the solid particles (reduced agglomeration). Published urinary chemistries, in conjunction with the computer programme SEQUIL, have been used to formulate a novel risk index for calcium stone formation independent of the traditional clinical classification of the stone former. Applying the risk index to three consecutive 24-hour urine samples of 39 untreated Ca stone formers showed that 35 (90%) patients produced at least one abnormal urine. Traditional single urinary parameter assessment, Ca/Cr, oxalate/Cr or citrate/Cr ratios, showed that only 17, 14, and 18% of the patients, respectively, had an abnormality, while taking all three together 24 (70%) had some abnormality and thus 30% were 'idiopathic' stone formers. Treatment regimens have been devised using the computer programme to return an abnormal urine to the normal according to the proposed risk index. In most urines two or more factors had to be changed simultaneously. Clinically there has been only one recurrence in 36 months, whereas before they had 4.4/3 years.