Hyponatraemia in older people as a sign of adrenal insufficiency: a case-control study.

BACKGROUND

Hyponatraemia is a common cause of hospitalisation in older adults. Adrenal insufficiency (AI) can result in hyponatraemia.

AIM: The aim of our study was to determine the frequency and characteristics of AI in elderly patients with hyponatraemia.

METHODS

Thirty patients ≥65 years with Na(+) ≤130 mmol/L and 30 age-matched control subjects, all hospitalised, were included in the study. Plasma cortisol levels were determined before and after intravenous administration of 1 µg synthetic adrenocorticotropin hormone. A peak cortisol >550 nmol/L was considered to exclude AI.

RESULTS

Sodium levels were 125 ± 5 and 139.8 ± 2 mmol/L in the hyponatremic and control groups respectively. Baseline cortisol <550 nmol/L was found in a half of hyponatremic patients. However, stimulated cortisol levels were compatible with AI in only one case (3%) and none of the controls. The mean cortisol levels were significantly higher in hyponatremic compared with control subjects, both in the basal state (585 ± 215 and 381 ± 135 nmol/L, respectively, P < 0.001) and after stimulation (933 ± 254 and 781 ± 160 nmol/L, P < 0.05). However, the incremental increase in cortisol levels after stimulation was similar in the two groups (361 ± 196 and 403 ± 155 nmol/L)

CONCLUSIONS

AI is an uncommon cause of hyponatraemia in older age. Based on this small cohort, AI may be present in 3% of elderly patients with hyponatraemia. AI cannot be excluded by baseline cortisol in a significant minority of hyponatremic patients and further testing with adrenocorticotropin hormone stimulation is needed.