Hyponatremia in sick children: a marker of serious illness.

To study the association between hyponatremia (serum sodium < or = 130 mEq/L) and the final outcome of the illness, we correlated serum sodium concentration at the time of hospitalization with the length of hospital stay and mortality in a prospective study of 727 sick children aged upto 12 years, who sought emergency care. The mean +/- SE duration of hospital stay (7.7 +/- 0.4 days) among 217 children with serum sodium < or = 130 mEq/L was about 30% longer than that of 510 children with serum sodium > or = 131 mEq/L (5.9 +/- 0.3 days) (p < 0.01). This remained unaffected by the sex and the age group, but was further prolonged in children with hypotonic--euvolemic type of hyponatremia as compared to those with hypovolemic hyponatremia. The mortality rate in 510 children with normal serum sodium concentration (> or = 131 mEq/L) was 5.3%. In contrast, it was 17% in 47 children with serum sodium < 125 mEq/L (Relative Risk 3.2; 95% Confidence Interval 1.6-6.7) and 9.3% in 170 children with serum sodium between 126-130 mEq/L (Relative Risk--1.8; 95% Confidence Interval 1.1-3.7) (p < 0.01). Hyponatremia in acutely ill children at admission indicates a poor prognosis.