Endocrine Abstracts

Introduction: Hyponatremia is the most prevalent electrolyte disturbance in hospitalized patients. Seasonal variation with higher incidence of profound hyponatremia during summer months has been described for patients in the emergency department setting. Whether this observation is also true among medical inpatients is unknown. This study aimed at analyzing the seasonal incidence of hyponatremia as well as sex and age specific differences among medical inpatients.

Methods: Medical inpatients diagnosed with hyponatremia between January 2009 and December 2015 using prospective administrative data were included in this nationwide cohort study. The primary outcome was the monthly alteration in hyponatremia incidence. Secondary outcomes were the impact of outdoor temperature on hyponatremia incidence and differences among sex and age groups.

Results: Of the 2,426,722 medical inpatients included in this study, 84,210 were diagnosed with hyponatremia, of whom 61% (n=51,262) were female. There was a strong seasonal variation in the incidence of hyponatremia. While the highest overall incidence of hyponatremia was observed in July (9.2%, n=8,976), it was lowest in December (5.5%, n=6,530). The overall incidence of hyponatremia in men was lower by 37% (OR 0.63 [95% CI 0.62 to 0.64]) compared to women. Sex-specific difference was most pronounced in the warmest month of July (mean temperature 20.1°C, OR 0.57 [95% CI 0.54 to 0.59]). The strongest association between seasonality and hyponatremia was seen in elderly female inpatients admitted during summer.

Conclusions: The incidence of diagnosed hyponatremia in medical inpatients increases during summer months with higher outdoor temperature. Association between seasonality of hyponatremia and outdoor temperature was most pronounced in elderly female inpatients.