Extreme Heat, Health Care Use, And Costs: Evidence From Commercial Insurance, Medicaid, And Medicare Advantage Authors: Jeff Romine jeff.romine@carelon.com, Amy Liu, Daniel Cullen, Katelyn Tang, Hakon Mattson, Mark Talavera, Arax Nazarian, Melissa Clarke, and Winnie C. Chi

https://www.healthaffairs.org/doi/10.1377/hlthaff.2025.01665?utm_campaign=may%202026%20issue&utm_medium=email&_hsenc=p2ANqtz--Vt36HO4mAu_7IvVmr_bIBW-deuIfWTcmamcsGbifF3-gFOSFCTKL--ZBYsRdWBLkVVEWyGbfcWApxkcnXZYufCeaLQg&_hsmi=415566602&utm_content=ahead%20of%20print&utm_source=hasu Extreme heat events have been demonstrated to increase emergency department (ED) visits, hospitalizations, and mortality, but evidence of their impacts on the associated costs and on outpatient use is more limited. We used 2016–23 health insurance claims from a large, national insurer and national temperature and humidity data to conduct a regression analysis on the relationship between extreme heat exposure and ED, inpatient, and outpatient use and cost in the commercial insurance, Medicaid, and Medicare Advantage (MA) populations. One additional day with a heat index of 100°F or hotter within a week was associated with increased ED use and cost across nearly all coverage populations and age groups. Extreme heat was associated with significant increases in inpatient use for children with commercial coverage (1.4 percent), members ages 18–64 with Medicaid coverage (0.47 percent), and MA members (0.5 percent) but was not associated with statistically significant increases in inpatient cost for any population group. It was not associated with increases in outpatient use or cost in any population group. MA members had the highest annual cost due to extreme heat. These findings provide evidence to inform population health management strategies, seasonal preparedness planning, and policy interventions to mitigate heat-related morbidity and health care costs.