Heat Index and Kidney Stone Recurrence Among Patients With Nephrolithiasis in a Veterans Affairs Population

To evaluate the association between heat index and kidney stone recurrence in a national Veterans Affairs cohort of kidney stone formers.

This retrospective cohort study of patients with an index kidney stone event from 2010 to 2020 used Veterans Healthcare Administration data. Heat exposure was defined as the number of days per year exceeding the 95th percentile heat index and was modeled both as a continuous and categorical (quartiles) variable. Cox proportional hazards models, additionally adjusting for demographics, rurality, social deprivation, and high-risk status for kidney stone recurrence, were used to assess the association with subsequent stone recurrence.

Among 136,340 patients, crude rates of recurrence ranged from 10.1% in the second quartile to 12.7% in the fourth quartile of heat exposure over the 7-year follow-up period. In adjusted analysis, patients in the highest quartile of heat exposure had a 5% greater risk compared with the lowest quartile (HR, 1.05; 95% CI, 1.01-1.10; P = .028). Modeling heat exposure as continuous, each 10-day increase in annual extreme heat days was associated with a 3% higher risk (HR, 1.03, 95% CI, 1.01-1.05); P = .003).

Higher heat index is associated with kidney stone recurrence risk in U.S. veterans. These findings suggest clinicians should consider environmental heat index when counseling high-risk patients.