Effects of sub- and supraoptimal indoor temperatures on kidney injury in home-bound frail elderly patients: A pilot case-crossover study

BACKGROUND/PURPOSE: With the acceleration of global warming, environmental temperature extremes pose health risks, particularly for frail older adults. This exploratory pilot study aimed to investigate associations between indoor temperatures and kidney injury in home-bound, frail, elderly patients. METHODS: This pilot case-crossover study included 32 frail, older adult patients receiving home-based care, which included continuous monitoring of the indoor environment and quarterly assessment of biomarkers. Possible kidney injury (pKI) was defined by rapid (eGFR) decline, with alternative definitions for sensitivity analysis. RESULTS: Among 284 kidney function tests, 84 met the pKI definition (29.6%). Both low and high indoor temperatures were associated with increased pKI risk, with significant cumulative lag effects: cold-season exposure beyond 43 days and warm-season exposure beyond 18 days. Changes in renal dysfunction biomarkers (e.g., copeptin, neutrophil gelatinase-associated lipocalin (NGAL), and heart rate variability (HRV) suggest that vasopressin and sympathetic pathways may be involved. CONCLUSIONS: Suboptimal indoor temperatures may trigger subclinical renal functional stress in frail older adults. Monitoring and adaptive strategies are necessary to mitigate risks associated with climate change.