Increased Ambient Temperature and Hyponatremia Presentations: A 10-Year Retrospective Study at an Australian Hospital.

Objective: To determine the relationship between ambient air temperature and the incidence of hyponatremia in a heat-prone region.

Methods: We conducted a retrospective study that correlated serum sodium concentrations documented at the Austin Hospital in Melbourne over 10 years from January 2014 to December 2023 with publicly available temperature data from the Australian Bureau of Meteorology. The main outcome measures were serum sodium concentrations and incidence of hyponatremia admissions when correlated to temperature, and, following heatwave events, defined as temperature above 30 °C over 5 consecutive days.

Results: Over this period, 45 718 low serum sodium results were identified from 26 557 unique patients. Serum sodium concentrations in January (Australian summer) were 0.55 mmol/L lower (95% CI 0.36 to 0.77, P < .001) than in September (Australian early spring). Women had lower sodium concentrations than men (-0.21 mmol/L, 95% CI -0.29 to -0.12, P < .001), as did patients older than 80 years when compared with those younger than 65 years (-0.39 mmol, 95% CI -0.50 to -0.29, P < .001). Hospital admissions with hyponatremia were more frequent during summer months. Profound hyponatremia admissions (sodium ≤125 mmol/L) were more frequent following a heatwave than without (7.6% vs 6.5%, P = .04).

Conclusion: Our study demonstrates that serum sodium concentrations are lower and profound hyponatremia-related hospital admissions higher when ambient temperatures are warmer. This suggests that hyponatremia is a climate-associated health issue. Local public health advice for water consumption during heatwaves should consider this risk, and prompt action to limit climate change is required to mitigate this risk.