Endocrine Abstracts

Background: Hyponatraemia is the most commonly observed electrolyte abnormality in hospitalised patients. The many causes of hyponatraemia may be classified either by volume status or aetiology. Thorough history taking, clinical examination and investigation are necessary in order to accurately determine the cause of hyponatremia and so formulate the most appropriate management plan.

Methods: Patients with serum sodium <131 mM were identified by daily automated search of the biochemistry database at Nottingham University Hospitals NHS Trust over a 2 week period (September 2012). Seventy-five patients fulfilled these criteria. Data regarding clinical history, examination of volume status, investigations undertaken, diagnosed aetiology of hyponatraemia, length of hospital stay and treatment were extracted retrospectively from the medical notes using a linked anonymised system.

Results: Patients, 53% female of average age 76.0 (±13.0), had serum sodium 126.5 mM (±4.1), potassium 4.4 mM (±1.0), creatinine 116.8 μM (±133), plasma osmolarity 270.1 Osmol/kg (±22.4), urinary osmolarity 362 Osmol/kg (±141.7) and spot urinary sodium of 38.1 mM (±40.2). The average length of stay was 18.2 days (±26.1) and 43% had recorded an examination of volume status. The aetiology of hyponatraemia was established in 37.3% of patients. 11 patients were recorded as having SIADH but in only two of these were investigations sufficient to substantiate this conclusion. The most common aetiological association was malignancy (21%), heart failure (17%), thiazides (16%) and SSRIs (7%).

Conclusions: Hyponatraemia was usually an isolated electrolyte abnormality with normal serum potassium and mild renal impairment and affected a predominantly elderly population necessitating a hospital stay in excess of 2.5 weeks. There was room for improvement in clinical and laboratory investigation. The high prevalence of malignancy was notable and diagnosis of SIADH was particularly poorly substantiated.