Key Points:
Long-term recurrence data on pure metabolic calcium stone formers are limited.
The presented data highlight the importance of medical therapy in preventing future stones among high-risk patients.
Our study shows that the benefit of medical therapy may take 5 years to be evident; this fact should be considered in planning future studies.
Background: Long-term recurrence data on kidney stones are limited. We investigated stone recurrence in calcium-oxalate (CaOx) and calcium-phosphate (CaP) stone formers over a 10- to 12-year follow-up period.
Methods: We retrospectively identified patients from a surgical database with (1) CaOx or CaP stones, (2) postsurgical computed tomography imaging, and (3) at least 10 years of clinical follow-up and imaging. Data on medical therapy (MT), defined as being on thiazide/thiazide-like diuretic, potassium citrate, and/or allopurinol, were collected. Patients' records were reviewed for stone recurrence over a 10- to 12-year period. Associations between stone type, MT, and time to recurrence were analyzed with Kaplan–Meier survival curves and Cox proportional hazard models. Multivariate analysis was done using the Cox proportional hazard model.
Results: Of the 149 individuals who met inclusion criteria, 87 (58.3%) underwent baseline 24-hour urine testing, and 46 (30.8%) were prescribed MT in the form of thiazide (26/46; 57%), potassium citrate (25/46; 54%), and allopurinol (5/46; 11%). Compared with non-MT patients, patients on MT were more likely to have diagnosis of hypertension (P = 0.008) and be hypocitraturic at baseline (P = 0.01). Over a mean of 10.6 years, patients on MT had significantly fewer stone events compared with those not on MT (21.3% versus 37.5%, P = 0.04), with 8 (17%) individuals discontinuing their MT over the study period. Patients with predominantly CaP mineral subtype had more stone events than CaOx (64% versus 36%, P = 0.006), a phenomenon likely driven by higher baseline urine pH (>6, 58.8% versus 33.9%, P = 0.02). By survival analysis, the impact of stone subtype and MT became apparent at follow-up months 20 and 60, respectively.
Conclusions: In a population of calcium stone formers at high recurrence risk, patients with CaOx mineral subtype and on MT had the lowest stone event rate on long-term follow-up. These findings suggest that the beneficial effect of MT may take up to 5 years to become evident clinically and by surveillance imaging.