Serum sodium level is inversely correlated with body temperature in children

Several studies have demonstrated that non-osmotic antidiuretic hormone activity contributes to the development of hyponatremia in children with common febrile diseases. However, the relationship between hyponatremia and body temperature has remained unclear. We therefore examined this relationship in children with common diseases.

In this retrospective case study based on a chart review, 1,973 children presenting with acute illnesses at Hirakata City Hospital between November 2008 and October 2009, and for whom blood test data were available, were enrolled. The median age of this cohort was 2.7 years and the mean serum sodium concentration was 136.4 mEq/L; 454 patients showed hyponatremia (<135 mEq/L). The patients were classified into four groups on the basis of body temperature, <37 °C, 37 °C (37.0-37.9 °C), 38 °C (38.0-38.9 °C) and ≥39 °C, and their serum sodium concentration was compared.

The mean sodium level was significantly lower in febrile (135.9 mEq/L) than in non-febrile (138.5 mEq/L) patients. The mean serum sodium levels in the four temperature groups were, in ascending order, 138.5 mEq/L (95% CI, 138.3-138.8 mEq/L), 137.3 mEq/L (137.1-137.5 mEq/L), 136.1 mEq/L (135.8-136.3 mEq/L) and 134.6 mEq/L (134.4-134.9 mEq/L), respectively. The serum sodium level in each individual temperature range became significantly lower as body temperature increased (P < 0.001).

There is a clear inverse correlation between serum sodium level and body temperature in children with common febrile diseases, and fever may play an important role in this relationship.