Objective: Hyponatremia is the most common electrolyte imbalance. The initial treatment decision\nis based on clinical evaluation of patient volume status but an accurate assessment is\ndifficult, particularly differentiating mild hypovolemia from euvolemia. The aim of this study is to\nexamine if biomarkers are valuable in the early determination of volume status and SIADH\ndiagnosis. Methods: Blood samples were collected from an unselected patient population at entry\nto the Emergency Department. If the plasma sodium level (P-Na) was �125 mmol/L, the sample\nwas frozen for further analysis. Mid-regional pro-atrial natriuretic peptide (MR-proANP), proadrenomedullin\n(MR-proADM), C-terminal prepro-vasopressin (copeptin), pro-endothelin-1\n(proET-1) and N-terminal pro-brain natriuretic peptide (NT-proBNP) levels were analysed. A\ncomprehensive assessment of volume status and underlying causes was made after discharge\nblinded for biomarker results. Results: A total of 81 patients were included. A well substa ntiated\nvolemic state (hypo/eu/hypervolemia) was established in 72 patients (mean age 76 years, 65%\nwomen, median P-Na 119 mmol/L). A significant association was observed between MR-proANP\nlevels and volemic state (p = 0.0001). Data was specifically analysed with respect to distinguishing\nhypo- from euvolemia (n = 59) using logistic regression. In a crude analysis, MR-proANP was\nsignificantly related to euvolemia (OR: 2.54 per SD of MR-proANP, 95% CI 1.32 - 4.86, p = 0.005)\nand remained so after the multivariate backward elimination model (OR: 2.45 per SD of MRproANP,\n95% CI 1.22 - 4.91, p = 0.012.), whereas the other studied biomarkers were not. Copeptin\nlevels were not associated with a diagnosis of SIADH. Conclusions: MR-proANP may be of value in\nearly determination of volume status in hyponatremic patients.
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