Seasonal variation in the prevalence of profound hyponatremia (<125 mmol/l) in patients on admission to an acute hospital in Japan

Abstract

Hyponatremia is a common but important electrolyte disorder mostly complicated with other diseases. Recently, we experienced a case of a hypertensive patient in her seventies taking a thiazide diuretic, who presented with disorientation due to severe hyponatremia (serum sodium level, 104 mmol/l) on admission. Taking this opportunity, patients with profound hyponatremia (<125 mmol/l) on admission were investigated. Patients newly admitted to Matsumoto Medical Center (an acute hospital) were surveyed retrospectively for one year from May 1, 2016 to April 30, 2017. Patients with profound hyponatremia on admission were selected, and their clinical characteristics were evaluated. A total of 108 out of 4223 patients (2.6%; 67 men, 41 women) showed profound hyponatremia, and 101 out of 108 patients were 65 years old and over. The prevalence of profound hyponatremia in the warm season of April to October (3.1%, 76 in 2444 patients) was significantly ( p = 0.002, χ2 test) higher than that in the cold season of November to March (1.8%, 32 in 1779 patients). The monthly prevalence tended to correlate with the monthly average temperature of the local area ( r = 0.517, p = 0.085). There were six patients treated with thiazide diuretics in the warm season, while there were no such patients in the cold season, not reaching a significant difference ( p = 0.240). The present study demonstrated an increased risk of hyponatremia in elderly patients during the warm season. Considering also the relevant literature, health professionals should pay enough attention to thiazide- or drug-induced hyponatremia and the impact of water/salt intake for heat exposure.