Heat-related acute kidney injury risk in England: a nationwide case-crossover analysis of 947,342 AKI alerts

Abstract Background Acute kidney injury (AKI) incidence is rising and while heat–AKI associations are established, the demographic and clinical groups most vulnerable remain unclear. Identifying these groups is essential for kidney-specific heatwave guidance. Methods 947,342 AKI alerts in England from April to September, 2017-2021, UK Renal Registry data were linked to HadUK-Grid dataset and hospital admission data. A time-stratified, bidirectional case-crossover design with distributed lag models estimated odds ratios (ORs) for AKI associated with temperatures above 25°C, stratified by demographic characteristics and admission diagnosis. Results Heat exposure was associated with AKI (OR 1.038; 95%CI 1.036–1.040 per 1°C rise above 25°C) with highest odds for stage 3 AKI (OR 1.047; 95%CI 1.039–1.055). Associations are more marked in males (OR 1.041; 95%CI 1.037–1.044) than females (OR 1.035; 95% CI 1.032-1.039); odds doubled in ≥85s (OR 1.054; 95%CI 1.049-1.060) compared to 45–64 years age group (OR 1.027; 95%CI 1.021-1.032). Ethnic risks varied: Chinese (OR 1.054, 95% CI: 1.012–1.098), White (OR 1.041; 95% CI 1.038–1.044), Indian (OR 1.033; 95% CI 1.019–1.047), Pakistani/Bangladeshi (OR 1.027; 95% CI 1.011–1.044), Caribbean (OR 1.024; 95% CI 1.005–1.042), and African (OR 1.001; 95% CI 0.982–1.021), with differences partly explained by younger age distribution in ethnic minority groups. Heat-related AKI was more marked for admissions of patients with delirium (OR 1.061; 95% CI 1.029–1.094) and with respiratory diseases (OR 1.044; 95% CI 1.037–1.052). Conclusions There was effect modification by age for heat-related AKI risk, with especially high risks amongst older individuals; those admitted with delirium or respiratory illness and some ethnic groups. These findings support the development of targeted kidney-specific hot weather guidance to protect vulnerable populations identified.