Stone formers with state-assisted insurance (SAI) are more likely than those with private insurance to form calcium phosphate rather than calcium oxalate stones, according to a study.

Benjamin W. Herrick, MD, of Dartmouth Hitchcock Medical Center in Lebanon, N.H., and colleagues retrospectively reviewed data from 346 stone formers. SAI were more likely than privately insured patients to form calcium phosphate instead of calcium oxalate stones (77.4% vs. 10.1%), the researchers report online ahead of print in the Journal of Endourology.

Among patients with calcium stones, the likelihood of forming calcium phosphate stones over calcium oxalate stones was 10 times higher among those with state-assisted insurance compared with privately insured patients.

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In addition, SAI patients also had significantly higher urinary sodium, pH, and supersaturation of calcium phosphate compared with privately insured patients. They also had a lower supersaturation of uric acid.

“These findings may reflect dietary or other unmeasured differences, and have important implications for resource allocation and counseling, as treatment may differ for these groups,” the authors wrote.

Compared with privately insured patients, SAI patients were significantly more likely to be female (55% vs. 38%) and younger (43.5 vs. 49.2 years).