Reassessing the role of copeptin in emergency department admissions for hypotonic hyponatremia

The role of copeptin in assessing hyponatremic patients at emergency department (ED) admission remains debated.

To assess copeptin's effectiveness in evaluating extracellular fluid (ECF) volume and its predictive value in hyponatremic adults admitted to the medical ED.

Report from the IPSO-URG, a prospective cohort study with recruitment from June 2018 to August 2019 and 6-month follow-up.

The medical ED of a single tertiary center.

A consecutive sample of 123 adults with hyponatremia confirmed by direct and indirect ion-selective electrode assay after glucose correction. Excluding 33 with missing consent or criteria and 6 without hypotonic hyponatremia, 84 patients were analyzed.

Data included symptoms, vital signs, ultrasound, medical history, Charlson Comorbidity Index, and pre-treatment blood and urine samples.

ECF status was reassessed post-discharge by three endocrinologists, blinded to copeptin results, who classified cases etiologically and resolved disagreements through discussion. In-hospital and six-month mortality were recorded.

A copeptin-to-urinary sodium (u-Na) ratio ≤29.5 pmol/mmol increased the likelihood of preserved ECF >4-fold (OR 4.28, p=0.026), outperforming standard u-Na (AUC difference 0.177, p=0.013). Copeptin predicted in-hospital mortality (HR 1.005), with >60.1 pmol/L as the optimal cut-off (p=0.0005). Copeptin (HR 1.005, p=0.02), NT-proBNP (HR 1.004, p=0.031), and comorbidity burden (HR 1.207, p=0.009) predicted six-month mortality, with copeptin >13.6 pmol/L indicating >4-fold risk (HR 4.507, p=0.0001).

Measuring copeptin on ED admission in hypotonic hyponatremia aids diagnosis and mortality prediction. The copeptin/u-Na index more accurately identifies preserved ECF than the standard u-Na cut-off.

ClinicalTrials.gov ID: NCT04402190