Predictive value of kidney stone composition in the detection of metabolic abnormalities

Purpose To determine if kidney stone composition can predict the underlying medical diagnosis, and vice versa. Methods We studied 1392 patients with kidney stones who underwent a complete ambulatory evaluation and who submitted one or more stones for analysis. We ascertained the associations between medical diagnosis and stone composition. Results The most common kidney stones were composed of calcium oxalate (n = 1041 patients [74.8%]), mixed calcium oxalate–calcium apatite (n = 485 [34.8%]), and calcium apatite alone (n = 146 [10.5%]). The most common medical diagnoses were hypocitraturia (n = 616 patients [44.3%]), absorptive hypercalciuria (n = 511 [36.7%]), and hyperuricosuria (n = 395 [28.4%]). Calcium apatite and mixed calcium oxalate–calcium apatite stones were associated with the diagnoses of renal tubular acidosis and primary hyperparathyroidism (odds ratios ≥2), but not with chronic diarrheal syndromes. As the phosphate content of the stone increased from calcium oxalate to mixed calcium oxalate–calcium apatite, and finally to calcium apatite, the percentage of patients with renal tubular acidosis increased from 5% (57/1041) to 39% (57/146), and those with primary hyperparathyroidism increased from 2% (26/1041) to 10% (14/146). Calcium oxalate stones were associated with chronic diarrheal syndromes, but not with renal tubular acidosis. Pure and mixed uric acid stones were strongly associated with a gouty diathesis, and vice versa. Chronic diarrheal syndromes and uric acid stones were associated with one another, and brushite stones were associated with renal tubular acidosis. As expected, there was a very strong association between infection stones and infection, and between cystine stones and cystinuria. Conclusion Stone composition has some predictive value in diagnosing medical conditions, and vice versa, especially for noncalcareous stones.