Linking basic principles of solution chemistry to kidney stone formation timelines.

Kidney stone formation remains enigmatic, largely because of its multifactorial nature, and because assessment is by necessity based mostly on a posteriori analysis and/or on specific analyses (e.g., prescribed components found in urine) that focus on particular conditions. Here, we offer a different perspective to assess overall aspects of stone formation, delineating a method to calculate minimum times of stone formation as a function of stone type (calcium oxalate, calcium phosphate, and uric acid) and size (up to 10 mm), in the form of the pure mass of the stone, without consideration of actual formation or aggregation causes or processes. The calculations thus represent characteristic measures that delineate limits on times required to form specific stone volumes as a function of chemical content and mass. The times to form each stone type and specific size vary considerably, ranging from days to years. A key factor is the amount of the "building block" material in urine that actually contributes to stone formation, i.e., the % yield from solution to solid phase. In some cases, unrealistically high yields (e.g., 5-10%) are required to form a stone with a specified size, type, and time; this indicates that other factors - at least some of which can be deduced from the analysis - play key roles in stone formation. This information thus provides estimates that constrain assessments of stone formation mechanisms and interpretation of clinical findings.