Hyponatremia among the institutionalized elderly in 2 long-term care facilities in Taipei

Hyponatremia is common in the institutionalized elderly, and syndrome of inappropriate antidiuretic hormone secretion was deemed the most important etiologic factor. The purpose of this study was to evaluate the prevalence and etiologic factors of hyponatremia among institutionalized elderly and to explore its association with nutritional status.

Subjects in 2 private long-term care facilities (LTCFs) participated in this study. Periodic nutritional evaluations, including anthropometric measurements and serial laboratory examinations, were performed every 6 months. When hyponatremia was identified, serum osmolality, serum levels of cortisol, thyrotropin, antidiuretic hormone, urine osmolality, and electrolyte profile were done instantly. Water loading tests were performed for subjects with euvolemic, hypo-osmolar hyponatremia. Nutritional status (i.e. hemoglobin, serum albumin, serum total cholesterol, body mass index [BMI], and mean body weight loss within 6 months) was compared between hyponatremic and normonatremic subjects during hyponatremic episodes and at follow-up (6 months later).

In total, 67 (mean age = 77.2 +/- 8.8 years, M/F = 45/22) LTCF residents were enrolled. The prevalence of hyponatremia was 31.3% (21/67) during the 6-month period, and 62.5% of these cases were related to reset osmostat. In addition, BMI was similar between hyponatremic and normonatremic subjects during hyponatremic episodes (19.1 +/- 3.2 vs 20.5 +/- 4.0 kg/m2, p = 0.16), but became significantly lower in hyponatremic subjects 6 months later (18.5 +/- 3.2 vs 20.8 +/- 4.2 kg/m2, p = 0.027). However, the mean body weight loss during the 6-month follow-up was similar (3.0% vs 0.8%, p = 0.25). Furthermore, hemoglobin and serum levels of albumin were similar between groups during hyponatremic episodes and at follow-ups, but serum levels of total cholesterol were significantly lower in hyponatremic subjects on both occasions (166.9 +/- 30.5 vs 190.2 +/- 38.2 mg/dL, p = 0.016 during hyponatremic episodes and 153.6 +/- 29.4 vs 182.8 +/- 35.5 mg/dL, p = 0.003 at follow-up).

About a third of LTC-dwelling elderly would experience hyponatremia during the 6-month period, and 62.5% of them were due to reset osmostat. The relationship between hyponatremia and undernutrition deserves further investigation.