What Is a Sodium Test?
A sodium test measures the amount of sodium in your blood. It’s most commonly included in a Basic Metabolic Panel (BMP) or Electrolyte Panel, which are routine blood tests used to assess your overall health and detect imbalances in fluid and electrolytes.
Why Is This Test Important?
Sodium is a vital electrolyte that helps regulate:
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Fluid balance
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Nerve and muscle function
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Blood pressure
Your body maintains sodium levels within a tight range through the kidneys and hormones like aldosterone and antidiuretic hormone (ADH). Monitoring sodium is essential because both too much and too little can lead to serious health issues.
When Is a Sodium Test Ordered?
A sodium test may be ordered:
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As part of a routine health check (e.g., BMP or electrolyte panel)
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If you have symptoms of electrolyte imbalance, such as confusion, weakness, or fatigue
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If you're experiencing dehydration or fluid retention (edema)
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To monitor chronic or acute illnesses involving the brain, heart, lungs, liver, kidneys, thyroid, or adrenal glands
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If you're taking medications that affect sodium levels, such as diuretics
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After surgery, serious illness, or receiving intravenous (IV) fluids
Related Tests
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24-hour urine sodium test: Helps assess how much sodium is being excreted, especially useful when blood sodium levels are abnormal.
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Electrolyte panel: Includes sodium, potassium, chloride, and bicarbonate.
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Basic Metabolic Panel (BMP): Includes sodium, potassium, chloride, calcium, glucose, creatinine, blood urea nitrogen (BUN), and bicarbonate.
What Do Abnormal Sodium Levels Mean?
Low Sodium (Hyponatremia)
May be caused by:
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Drinking too much water
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Kidney disorders
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Heart, liver, or hormonal problems
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Certain medications
High Sodium (Hypernatremia)
May result from:
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Dehydration
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Excess fluid loss (e.g., vomiting, diarrhea, sweating)
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Not drinking enough water
Symptoms of Imbalance
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Headache or confusion
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Fatigue or muscle cramps
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Seizures (in severe cases)
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Coma (in extreme cases)
How the Body Regulates Sodium
The body controls sodium balance through:
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Hormones: Such as aldosterone (retains sodium) and natriuretic peptides (eliminate sodium)
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Thirst mechanism: Even a 1% increase in sodium can trigger thirst to restore balance
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Kidney function: Filters and excretes excess sodium through urine
Sodium comes primarily from your diet, especially from table salt (sodium chloride) and processed foods. The kidneys help eliminate any excess.
What Are Electrolytes?
Electrolytes are charged minerals found in blood and body fluids. They help:
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Maintain fluid balance
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Support muscle contractions
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Transmit nerve signals
Main electrolytes include:
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Sodium
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Potassium
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Chloride
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Bicarbonate (CO2)
Normal Sodium Range
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135 – 145 mEq/L (milliequivalents per liter)
Note: Reference ranges may vary slightly depending on the laboratory.
References
Sodium - labtestsonline.org/understanding/analytes/sodium/tab/test/
Lewis, J. L. (n.d.). Hypernatremia (High level of sodium in the blood)
merckmanuals.com/home/hormonal-and-metabolic-disorders/electrolyte-balance/hypernatremia-high-level-of-sodium-in-the-blood
Takahashi, P. (2014, July 8). Why is low blood sodium a health concern for older adults? How is it treated? Retrieved from
mayoclinic.com/health/low-blood-sodium/AN00621
References:
Al-Awqati Q. Disorders of sodium and water. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 108.
Oh MS, Briefel G, Pincus MR. Evaluation of renal function, water, electrolytes, and acid-base balance. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 15
Sodium, Serum (Natrium)
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