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

OBJECTIVE: To evaluate the association between heat index and kidney stone recurrence in a national Veterans Affairs cohort of kidney stone formers. METHODS: This retrospective cohort study of patients with an index kidney stone event from 2010-2020 used Veterans Healthcare Administration data. Heat exposure was defined as 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. RESULTS: 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 seven-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 to 1.10; P=0.028). 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 to 1.05); P=0.003). CONCLUSION: 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.