Major extracellular electrolyte ion
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About Sodium
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About Sodium
Overview and History
Sodium is a chemical element present in the body almost entirely as the charged ion Na+. Biochemically it is classified as a major extracellular cation; its distribution across cell membranes and concentration in plasma are maintained by renal handling, membrane transporters, and hormonal regulators that influence water and salt balance.
Clinical measurement of sodium in serum or plasma is a long-established laboratory assay used to assess fluid and electrolyte status. Modern analyzers quantify sodium quickly and reliably; in cardiovascular assessment, sodium levels are interpreted alongside kidney function, osmolality, and vascular markers to understand systemic volume and hemodynamic context.
Interpreting Highs and Lows
Elevated serum sodium most often reflects a relative water deficit compared with sodium concentration — for example from reduced water intake, increased water losses, or altered renal water handling — and can be associated with higher circulating volume load and changes in vascular tension. Low serum sodium typically indicates relatively more water compared with sodium in the bloodstream, which can result from fluid retention, impaired water excretion, or hormonal shifts that affect water balance. Because sodium reflects the balance of water and salt, its clinical meaning is best interpreted in the context of the full panel (renal markers, osmolality, other electrolytes, and vascular or cardiac tests) and the clinical picture.
Featured Test
Cardio Zoomer includes serum sodium because it is a fundamental indicator of fluid balance and vascular loading. Combined with renal, endothelial, and cardiac stress markers, sodium helps clinicians distinguish whether volume shifts or water–salt handling are contributing to altered hemodynamic patterns, improving personalization of cardiovascular assessment.
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Mary Beth Augustine
DCN, RDN, FAND- Lead Clinical Educator
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MSc- MHNE- Clinical Educator
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Adair Anderson
MS, RDN, LDN- Clinical Educator
Lillie Luu Nguyen
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Jason Barker
ND- Clinical Educator
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ND- Clinical Educator
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DCN, CNS, LDN- Clinical Educator
Jessy Dhanjal
ND- Clinical Educator
Nour Amri
MS, LDN, CNS, CKNS- Clinical Educator
