Prevalence of hyponatremia among medically hospitalized patients and associated outcomes: a retrospective cohort study.

Background: Hyponatremia is a common electrolyte disturbance among hospitalized patients and is linked to increased mortality as well as poor outcomes.

Objectives: Study the prevalence of hyponatremia among medically admitted patients and the outcomes associated with hyponatremia.

Design: Retrospective cohort.

Setting: Medical ward at tertiary hospital setting.

Patients and methods: The study included adult (≥18 years) hospitalized patients in general medical wards. Three readings of serum sodium level were taken (initial sodium level, nadir during admission, and before discharge).

Sample size and basis: The sample size of 350 was determined based on a presumed 35% incidence of hyponatremia among hospitalized patients, with a 5% error margin.

Main outcome measures: The prevalence of hyponatremia among medically hospitalized patients and association with health outcomes including length of hospital stay, inpatient mortality, 90-days readmission and 1-year mortality.

Results: In this study, 736 patients met the inclusion criteria. Of these, 377 (51.2%) had hyponatremia on admission, increasing to 562 (76.35%) during hospitalization. Mild hyponatremia was observed in 49.6% (n=365), moderate in 13.6% (n=100), and severe in 13.2% (n=97). Severe hyponatremia patients were significantly older (P<.01), predominantly female (P=.014), and had lower serum magnesium and albumin levels (P<.01). Hypertension, ischemic heart disease, heart failure, and diabetes were more prevalent in severe hyponatremia cases (P<.01, P<.01, P=.045, P<.01, respectively). Hospital stays were significantly shorter for patients with normal sodium levels (P<.01). Patients with severe hyponatremia had a shorter time for first hospital readmission (HR=0.80, P<.01 [95% CI; 0.69-0.94]).

Conclusion: Hyponatremia was prevalent among medically hospitalized patients and more common among old patients, women, and patients with comorbidities. Hyponatremia was associated with increased length of stay in hospital and increased risk of 90-day re-admission.

Limitations: Single-centre design and retrospective nature.