Risk factors in calcium stone disease of the urinary tract.

The concept that calcium stone formation may be explained on the basis of a number of risk factors is developed. The main risk factors involved are shown to be calcium, oxalate, pH, acid mucopolysaccharides and uric acid. A method is described for calculating and combining the individual risk factors into a measure of the "relative probability" of forming stones (PSF). PSF values are generally lower in normal subjects than in stone-formers. Amongst the normals, PSF values are lower in children and women than in men. Recurrent stone-formers have the highest PSF values and these correlate well with the severity of the diseases as defined by the stone episode rate of the patient. Single stone-formers have PSF values intermediate between those of normal men and those of recurrent stone-formers.