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Introduction: A relationship between nephrolithiasis and socioeconomic status (SES) has been suggested but remains undefined. We examined stone composition, 24-hour urinary risk factors and SES in patients evaluated in two regional stone clinics to elucidate whether a relationship exists.
Methods: We performed a retrospective review of stone formers who completed a 24-hour urinalysis as part of a metabolic evaluation for nephrolithiasis. We used state-assisted, need-based health insurance (SAI) as a surrogate for lower SES and compared these patients to those with private insurance (PI). Baseline characteristics were compared including stone composition when available. Multivariate analyses were performed adjusting for known risk factors for stones.
Results: 346 patients were included. Patients with SAI (16%) were significantly more likely to be female (55% vs. 38%, p=0.026), and younger (43.5 vs. 49.2, p=0.003). Among those with stone composition data (200), those with SAI were as likely to form calcium phosphate (CaPhos) as calcium oxalate (CaOx) stones (46.9% vs. 31.3%, p=0.436). Patients with PI were significantly less likely to form CaPhos than CaOx stones (77.4% vs. 10.1%, p<0.001). On multivariate analysis, patients with SAI had significantly higher urine sodium, supersaturation of CaPhos, and pH and lower supersaturation of uric acid compared to patients with private insurance.
Conclusion: Those with SAI have an increased likelihood of CaPhos stones than patients with PI, which is supported by the significant differences in their 24-hour urine profiles and may reflect dietary differences. This data has important implications for resource allocation, as metabolic and surgical approaches may differ for these stones.