Sodium, Serum (Natrium)

check icon Optimal Result: 134 - 144 mmol/L.

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:

  • Fluid balance

  • Nerve and muscle function

  • 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:

  • As part of a routine health check (e.g., BMP or electrolyte panel)

  • If you have symptoms of electrolyte imbalance, such as confusion, weakness, or fatigue

  • If you're experiencing dehydration or fluid retention (edema)

  • To monitor chronic or acute illnesses involving the brain, heart, lungs, liver, kidneys, thyroid, or adrenal glands

  • If you're taking medications that affect sodium levels, such as diuretics

  • After surgery, serious illness, or receiving intravenous (IV) fluids


Related Tests

  • 24-hour urine sodium test: Helps assess how much sodium is being excreted, especially useful when blood sodium levels are abnormal.

  • Electrolyte panel: Includes sodium, potassium, chloride, and bicarbonate.

  • 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:

  • Drinking too much water

  • Kidney disorders

  • Heart, liver, or hormonal problems

  • Certain medications

High Sodium (Hypernatremia)

May result from:

  • Dehydration

  • Excess fluid loss (e.g., vomiting, diarrhea, sweating)

  • Not drinking enough water

Symptoms of Imbalance

  • Headache or confusion

  • Fatigue or muscle cramps

  • Seizures (in severe cases)

  • Coma (in extreme cases)


How the Body Regulates Sodium

The body controls sodium balance through:

  • Hormones: Such as aldosterone (retains sodium) and natriuretic peptides (eliminate sodium)

  • Thirst mechanism: Even a 1% increase in sodium can trigger thirst to restore balance

  • 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:

  • Maintain fluid balance

  • Support muscle contractions

  • Transmit nerve signals

Main electrolytes include:

  • Sodium

  • Potassium

  • Chloride

  • Bicarbonate (CO2)


Normal Sodium Range

  • 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

What does it mean if your Sodium, Serum (Natrium) result is too high?

Elevated Sodium levels:

Hypernatremia means high levels of sodium in the blood. It’s defined as levels that exceed 145 mEq/L

Symptoms of hypernatremia include:

  • thirst
  • fatigue
  • swelling in hands and feet
  • weakness
  • insomnia
  • rapid heartbeat
  • coma

Hypernatremia is most often a problem in older adults, infants, and people who are bedridden. 

Causes of hypernatremia include:

  • not drinking enough water
  • drinking salty water
  • eating too much salt
  • excessive sweating
  • diarrhea
  • low levels of hormones such as vasopressin
  • high levels of aldosterone
  • Cushing’s syndrome, caused by excessive cortisol

Certain medications can also potentially cause hypernatremia. These include:

  • birth control pills
  • corticosteroids
  • laxatives
  • lithium
  • nonsteroidal anti-inflammatory pain medications

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What does it mean if your Sodium, Serum (Natrium) result is too low?

Understanding Hyponatremia: Low Sodium Levels

Hyponatremia is a medical condition defined by abnormally low sodium levels in the blood, specifically when sodium concentration falls below 135 mEq/L. This imbalance occurs when there's too much water relative to sodium in the body.

Symptoms

Mild to Moderate Symptoms:

  • Nausea and vomiting
  • Headache
  • Fatigue or low energy
  • Muscle weakness or cramps
  • Confusion or disorientation
  • Irritability
  • Loss of appetite
  • Dizziness

Severe Symptoms:

  • Hallucinations
  • Seizures
  • Loss of consciousness
  • Potential coma

Cellular Impact

Hyponatremia can cause significant cellular damage by forcing cells to swell with excess water. This is particularly dangerous in critical areas like the brain, where swelling can lead to serious neurological complications.

Causes and Risk Factors

Medical Conditions:

  • Kidney disease
  • Liver disease or cirrhosis
  • Heart failure
  • Addison's disease
  • Underactive thyroid (hypothyroidism)
  • Hormonal imbalances (SIADH)

Medication-Related Causes:

  • Diuretics
  • Antidepressants
  • Certain pain medications

External Factors

  • Severe diarrhea or vomiting
  • Large skin burns
  • Excessive sweating
  • Drinking excessive water
  • Inadequate urination
  • Presence of ketones in blood (ketonuria)

Who is Most at Risk?

  • Older adults
  • Individuals with chronic medical conditions
  • People taking multiple medications
  • Endurance athletes
  • Those with hormonal disorders

Potential Complications

  • Rapid brain swelling
  • Neurological damage
  • Seizures
  • Potential coma
  • In extreme cases, life-threatening consequences

Prevention and Management

  • Monitor sodium levels in at-risk individuals
  • Stay hydrated but avoid excessive water intake
  • Manage underlying medical conditions
  • Review medications with healthcare providers
  • Seek immediate medical attention if symptoms persist or worsen

When to Seek Medical Help?

Consult a healthcare professional if you experience:

  • Persistent symptoms of low sodium
  • Confusion or disorientation
  • Severe headaches
  • Unexplained muscle weakness
  • Prolonged nausea or vomiting

Note: This information is for educational purposes and should not replace professional medical advice. Always consult with a healthcare provider for personalized guidance.

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