Association between ambient temperature and first recorded hospitalizations for acute kidney injury in Taiwan: a nationwide case-crossover study

Although substantial epidemiological evidence has demonstrated associations between high temperatures and acute kidney injury (AKI), few studies have focused on initial AKI events or examined heterogeneity in heat-related risk across population subgroups, particularly occupational groups. This study aimed to examine the short-term effects of ambient temperature on first recorded AKI hospitalizations and to assess heterogeneity across demographic, clinical, occupational, and socioeconomic subgroups. We conducted a nationwide time-stratified case-crossover study of 474,949 first recorded AKI hospitalizations in Taiwan between 2008 and 2019 using data from the National Health Insurance Research Database. Associations between ambient temperature and AKI hospitalization were estimated using conditional logistic regression with distributed lag non-linear models over lag days 0–6. The main model focused on temperature exposure, while relative humidity and major ambient air pollutants were additionally evaluated in sensitivity analyses. Effect heterogeneity was examined across demographic, comorbidity, occupational, and socioeconomic subgroups. A J-shaped exposure–response relationship was observed, with the risk of AKI hospitalization increasing markedly at higher temperatures. Compared with the minimum morbidity temperature (MMT) of 3.9 °C, the OR at 33 °C was 1.530 (95% CI: 1.313–1.783). Above the 90th percentile of daily mean temperature (29.98 °C), each 1 °C increase was associated with a 14.2% increase in the odds of AKI hospitalization (OR = 1.142; 95% CI: 1.116–1.169). The estimated attributable fraction associated with temperatures above the MMT was 5.5%. The temperature-associated risk was greatest on the day of exposure and attenuated at later lags, indicating a predominantly acute effect. Significant effect modification was observed by age, hypertension, and diabetes status, whereas differences by sex, chronic kidney disease, occupation, and socioeconomic status were not statistically significant. Elevated ambient temperature may act as an acute trigger of first recorded AKI hospitalization. The association varied across age and comorbidity groups, highlighting heterogeneity in susceptibility to heat-related AKI. These findings support incorporating kidney health into heat action plans and considering population-specific susceptibility when developing strategies to reduce heat-related kidney injury.