Endocrine Abstracts

Aims

To define the prevalence of hyponatraemia (serum sodium <135 mmol/l) on our medical admissions unit and review the laboratory investigations, diagnosis and management of patients with critical or severe hyponatraemia (serum sodium <120 mmol/l).

Methods

Serum sodium levels requested from the medical admissions unit over a six-month period were retrospectively collated. Case notes and biochemistry data were reviewed for all patients with serum sodium <120 mmol/l.

Results

Serum sodium levels had been requested on a total of 3593 individual patients, among whom the prevalence of hyponatraemia was 22.2%. Thirty two (32) patients had severe hyponatraemia, of whom three died in hospital. Complete case records were obtained in 30/32 cases, among whom the major causes of hyponatraemia were diuretics (27%), carcinoma (13%) and lower respiratory tract infection (7%). However, urine sodium and serum/urine osmolalities had only been checked in 20/30 cases. There were thus inadequate data to support an accurate diagnosis in 6/30 (20%) of cases (most of them labelled with the Syndrome of Inappropriate AntiDiuretic Hormone secretion). Overall, SIADH had been diagnosed in 37% of severe hyponatraemia cases, often without adhering to recognised diagnostic criteria.

Conclusions

Severe hyponatraemia is associated with high-levels of patient morbidity and mortality. A careful assessment of drug history, clinical volume status and serum/urine biochemistry is a prerequisite for optimal management. SIADH still appears to be the ‘default’ diagnosis all too often, rather than being confirmed through the necessary clinical and biochemical criteria.