Risk factors for the development of hyponatremia in psychiatric inpatients.

BACKGROUND: When inpatients who are on psychiatry services develop hyponatremia, medical consultation is usually required for evaluation and management, thus halting or delaying psychiatric treatment. Risk factors for the development of hyponatremia in this population have not been studied.
METHODS: A case-control study of psychiatric inpatients in a tertiary care facility was performed. Sixty-four patients who had a serum sodium level of less than 130 mmol/L were identified; three control subjects were chosen from the inpatient psychiatry service for each case. Risk factors investigated included medications, psychiatric diagnoses, basic demographic variables, and medical comorbidities.
RESULTS: Univariate and logistic regression analyses revealed that, in addition to diuretic use (adjusted odds ratio, 8.2; 95% confidence intervals, 2.2 to 30.8), use of fluoxetine (adjusted odds ratio, 21.4; 95% confidence interval, 5.3 to 86.9), tricyclic antidepressants (adjusted odds ratio, 4.9; 95% confidence interval, 1.6 to 15.2), and calcium antagonists (adjusted odds ratio, 4.0; 95% confidence interval, 1.1 to 14.2) were all associated with the development of hyponatremia. Important comorbidities included elevated creatinine levels, chronic obstructive pulmonary disease, hypertension, systolic blood pressure, and diabetes. Although age was significantly associated with hyponatremia in univariate analyses, it was not significant in multivariate analyses.
CONCLUSIONS: Among psychiatric patients, hyponatremia is often associated with factors other than psychogenic polydipsia, including medications and medical comorbidities. Although elderly psychiatric inpatients seem to develop hyponatremia more often than younger patients, once drugs and comorbidities are taken into account, age does not appear to be a significant risk factor for hyponatremia in this population.