Hyponatremia in a hospital population.

The frequency, causes, and outcome of hyponatremia (plasma sodium less than 125 mmol/L), and the value of some routine investigations were studied during a six month period in a hospital population. The incidence and prevalence of hyponatremia were 1.5 and 2.6 per 100 patients per day, respectively. A majority of patients (75%) developed hyponatremia in the hospital. The commonest cause of hyponatremia was normovolemic hyponatremia (79 patients). Hypovolemic and hypervolemic hyponatremia were seen in 63 and 21 patients, respectively. Urine osmolality did not differ between the three groups, and was of little diagnostic value. The mortality in the hyponatremic patients was 41.7%.