Seasonal variation in the incidence of hyponatremia

To study the seasonal variation in the incidence of hyponatremia and to correlate it with the rainfall pattern.

Retrospective analysis of patients having serum sodium of less than 120 meq/L was done during the 24 months from March, 1995. Patients with fever, renal failure, cardiac failure, cirrhosis, hyperlipidemia, hyperproteinemia, patients taking diuretics and postoperative patients were also excluded. Average inpatient number and rainfall for each month was noted. Daily incidence of hyponatremia was expressed as percentage of total inpatients for each day and was compared with the rainfall.

A total of 353 patients had hyponatremia during the two years from March, 1995; 174 cases during the first year and 179 during the second year. Average inpatient strength was 302.17 +/- 21.41 during the first year and 313.67 +/- 12.94 during the next year. The incidence of hyponatremia was 0.24 +/- 0.096% between June and August and 0.1 +/- 0.04% between December and February (95% confidence interval 0.045-0.235, p < 0.01). Statistically significant correlation was observed between rainfall pattern and hyponatremia, r = 0.711, 95% confidence interval 0.478-0.913, p = 0.01 during 95-96 and r = 0.825, 95% confidence interval 0.478-0.949, p < 0.001, during 96-97.

Incidence of hyponatremia is higher during the peak southwest monsoon season with similar pattern for the study period of two years. Humidity and temperature may have important role in the manifestation of hyponatremia.