Sodium
Also known as: Na, Serum Sodium
What Does Sodium Measure?
Sodium (Na) is an electrolyte — a mineral that carries an electrical charge — and is the most abundant positively charged ion in the fluid outside your cells (extracellular fluid). A blood sodium test, often included in a basic or comprehensive metabolic panel, measures the concentration of sodium in your blood serum, typically expressed in milliequivalents per liter (mEq/L) or millimoles per liter (mmol/L). Sodium plays a central role in regulating the amount of water in and around your cells, and your kidneys tightly control sodium levels through a sophisticated feedback system involving hormones such as aldosterone and antidiuretic hormone (ADH).
Why Does Sodium Matter?
Maintaining proper sodium balance is critical for nearly every major body function. Sodium helps regulate blood pressure, supports nerve impulse transmission, enables proper muscle contraction (including the heart muscle), and controls fluid distribution throughout the body. Abnormal sodium levels — either too high (hypernatremia) or too low (hyponatremia) — can have serious or even life-threatening consequences, including confusion, seizures, coma, or cardiovascular instability. Because sodium imbalances often reflect underlying conditions such as kidney disease, heart failure, dehydration, or hormonal disorders, serum sodium is one of the most routinely ordered and clinically important lab tests in both inpatient and outpatient settings.
Normal Ranges
Males
136–145 mEq/L (mmol/L)
Females
136–145 mEq/L (mmol/L)
Children
136–145 mEq/L (mmol/L); neonates may range 133–146 mEq/L
Causes of High Levels
- Dehydration or inadequate water intake (most common cause)
- Excessive sweating, vomiting, or diarrhea without adequate fluid replacement
- Diabetes insipidus (insufficient ADH production or kidney resistance to ADH)
- Excessive sodium intake (e.g., high-salt diet, hypertonic saline administration)
- Hyperaldosteronism (excess aldosterone causes sodium retention)
- Certain medications such as corticosteroids or lithium
Causes of Low Levels
- Overhydration or excessive water intake (dilutional hyponatremia)
- Heart failure, cirrhosis, or nephrotic syndrome causing fluid retention
- Syndrome of Inappropriate ADH secretion (SIADH) — excess water retention
How to Improve Your Sodium
Diet
- If sodium is low: ensure adequate dietary salt intake from whole foods such as soups, cheese, and naturally salty foods, under medical guidance
- If sodium is high: reduce processed and packaged foods, which account for over 70% of dietary sodium intake
- Aim for the recommended daily sodium intake of 1,500–2,300 mg per day for most adults
- Stay well hydrated with plain water throughout the day to help kidneys regulate sodium balance
- Increase potassium-rich foods (bananas, potatoes, leafy greens) as potassium helps balance sodium levels
Supplements
- Oral rehydration salts (ORS) containing sodium and glucose for mild hyponatremia due to dehydration or illness — use as directed
- Electrolyte supplements containing sodium, potassium, and magnesium for athletes or heavy sweaters — choose products with 500–1,000 mg sodium per serving
- Avoid excess sodium supplements unless prescribed; over-supplementation can worsen hypernatremia
- Vasopressin receptor antagonists (vaptans) may be prescribed by a physician for SIADH-related hyponatremia
- Fludrocortisone (a mineralocorticoid) may be prescribed for sodium loss due to adrenal insufficiency — only under medical supervision
Related Biomarkers
Frequently Asked Questions
What does it mean if my sodium level is low on a blood test?
A low sodium level (below 136 mEq/L) is called hyponatremia and is one of the most common electrolyte abnormalities seen in clinical practice. It can be caused by drinking too much water, fluid retention from heart or kidney conditions, hormonal disorders like SIADH or Addison's disease, or certain medications like diuretics. Mild hyponatremia may cause no symptoms, but moderate to severe cases can lead to nausea, headache, confusion, fatigue, and in serious cases, seizures or coma. Always follow up with your doctor to determine the underlying cause.
What are the symptoms of high sodium (hypernatremia)?
High sodium (above 145 mEq/L), called hypernatremia, typically results from dehydration or excessive sodium intake. Symptoms often include intense thirst, dry mouth, decreased urination, fatigue, and in more severe cases, confusion, muscle twitching, irritability, and seizures. Elderly individuals and infants are particularly vulnerable. Treatment focuses on gradual rehydration — correcting sodium too quickly can cause dangerous brain swelling.
Can drinking too much water lower your sodium level?
Yes. Drinking excessive amounts of water in a short period can dilute the sodium in your blood, a condition known as dilutional or 'overhydration' hyponatremia. This is sometimes seen in marathon runners or endurance athletes who drink large quantities of plain water without replacing electrolytes. It can also occur in people with certain psychiatric conditions (psychogenic polydipsia). Using electrolyte drinks during prolonged exercise instead of plain water can help prevent this.