Key Benefits

• Check your body’s fluid balance by measuring blood sodium, the main extracellular salt.
• Spot dehydration or overhydration that disrupts cells and brain function.
• Clarify causes of fatigue, nausea, or seizures by detecting sodium imbalance.
• Explain low sodium from heart, liver, kidney, thyroid, or adrenal problems.
• Guide diuretic, SSRI, or fluid therapy decisions by flagging medication-related sodium shifts.
• Flag exercise-associated hyponatremia risk in endurance events or heavy fluid intake.
• Track recovery with sodium trends during heart failure, cirrhosis, or kidney disease.
• Best interpreted with potassium, chloride, creatinine, glucose, osmolality, and your symptoms.

What is Sodium?

Sodium is an essential mineral and the main positively charged particle (cation, Na+) dissolved in body fluids outside cells (extracellular fluid). You get it primarily from food and drink, largely as table salt (sodium chloride), and it is readily absorbed in the gut. The body does not "store" sodium in a single depot; instead, it moves continuously between the bloodstream and the fluid around cells. The kidneys constantly adjust how much sodium and water are excreted under the direction of hormones such as aldosterone and vasopressin (antidiuretic hormone, ADH).

Sodium sets the osmotic pull that holds water in the bloodstream and tissues, helping determine fluid balance, blood volume, and tissue hydration (plasma osmolality and tonicity). Its gradient across cell membranes, maintained by the sodium-potassium pump (Na+/K+-ATPase), powers nerve impulses, muscle contraction, and the transport of nutrients like glucose and amino acids (cotransport). Because it is the dominant extracellular cation, the sodium level measured in blood mainly reflects the balance between total body sodium and water and the actions of regulatory systems (renin-angiotensin-aldosterone system, natriuretic peptides, and ADH).

Why is Sodium important?

Sodium is the principal electrolyte outside your cells. It sets blood osmolality, pulls water where it needs to go, and keeps nerves firing, muscles contracting, and blood volume and pressure stable. Kidneys and hormones constantly fine‑tune it to protect the brain and circulation.

Most labs list a general range around 135–145. Healthiest outcomes sit near the middle. Serum sodium reflects the balance of water to dissolved salts, so it tracks hydration and kidney–hormone control more than day‑to‑day salt intake.

When sodium runs below range, there is excess free water relative to sodium (hypo‑osmolality). Cells swell—most critically in the brain—causing headache, nausea, confusion, gait instability, and in severe cases seizures or coma. It often accompanies certain medicines (diuretics), heart, liver, or kidney disease, SIADH, adrenal or thyroid deficiency, or overhydration during endurance exercise. Premenopausal women and children are more prone to brain swelling in acute drops. Pregnancy lowers the normal set point, but sudden declines remain dangerous.

When sodium is above range, body water is relatively low (hyper‑osmolality). Cells dehydrate and the brain shrinks, leading to thirst, lethargy, irritability, weakness, and seizures. Typical settings include dehydration from fever or diarrhea, diuretic losses, and diabetes insipidus. Infants and older adults are most vulnerable due to limited access to water or blunted thirst; in hospitals it often marks severe illness.

Big picture: Sodium links kidneys, vasopressin and aldosterone, the heart–vessel system, and the brain. Steady, mid‑range values signal healthy water balance. Chronic lows associate with falls and fractures; chronic highs with dehydration burden and higher mortality—useful clues to underlying physiology and long‑term risk.

What Insights Will I Get?

Sodium measures the concentration of sodium in your blood. It is the main driver of plasma tonicity—the balance of salt and water that keeps cells properly hydrated. This balance underpins nerve signaling, muscle contraction, brain function, and stable blood volume and pressure. Sodium reflects the coordination of thirst, vasopressin (antidiuretic hormone), kidney function, and aldosterone, linking it to cardiovascular, renal, and cognitive health.

Low values usually reflect too much water relative to sodium (dilutional hyponatremia). This happens with excess vasopressin (SIADH), heart, kidney, or liver failure, diuretics, very low solute intake, too little thyroid hormone, or low adrenal hormones. It can also be “translocational” with high blood sugar. Effects often involve the brain—headache, imbalance, confusion, and falls—from cell swelling (cerebral edema). Older adults are more susceptible; premenopausal women have higher risk of severe symptoms.

Being in range suggests effective osmoregulation: intact thirst–vasopressin signaling, adequate kidney handling of water and salt, and stable blood volume. This supports steady cognition, neuromuscular function, and cardiovascular stability. For most adults, values cluster around the mid-portion of the usual reference interval.

High values usually reflect water loss exceeding sodium (hypernatremia). Common drivers include dehydration, fever, diarrhea, osmotic diuresis from high glucose, or diabetes insipidus (low or ineffective vasopressin). Limited access to water is a frequent factor. Brain cells shrink in this state, causing irritability, lethargy, or confusion. Infants and older adults are particularly vulnerable.

Notes: Pregnancy resets osmoregulation, slightly lowering sodium. Acute illness, medications (diuretics, antidepressants, antiepileptics, desmopressin), IV fluids, and endurance exercise can shift values. High glucose lowers measured sodium, and certain lab methods can artifactually lower it with very high lipids or proteins.