Practical outpatient evaluation for recurrent nephrolithiasis

An important aspect of recent progress in urolithiasis research has been the discovery that certain metabolic derangements may be associated with and may play a pathogenetic role in renal stone formation. The goal of an outpatient evaluation is to identify, as economically and efficiently as possible, the particular physiologic defect present in a given stone-former so that selective, rational therapy can be applied. Such an evaluation should be capable of detecting primary hyperparathyroidism, renal tubular acidosis, intestinal diseases that cause hyperoxaluria, and stones composed of uric acid, cystine, or struvite. In each of these instances, a selective treatment program is required. However, for the remaining 80 to 90 per cent of calcium stone-formers, many believe that diagnostic efforts are largely unwarrranted since most of these patients respond to a thiazide diuretic. Why bother to determine whether a patient with calcium nephrolithiasis has absorptive hypercalciuria, renal hypercalciuria, hyperuricosuria, or no detectable physiologic abnormality if thiazide diuretics reduce the incidence of stone recurrence in each circumstance? The answer to this important question determines the extent of the metabolic evaluation.