What is the concentration of Na+ in blood?

January 4, 2026 •

4 min read

The normal concentration of Na+ in blood is a tightly regulated parameter, typically ranging between 135 and 145 millimoles per liter (mmol/L). This balance is critical for numerous physiological functions, including fluid balance, nerve transmission, and muscle contraction.

Quick Summary

The normal concentration of Na+ in blood, known as serum sodium, is between 135 and 145 mmol/L. Imbalances can result in hyponatremia (low) or hypernatremia (high), leading to serious health issues if left untreated. The kidneys and hormones meticulously regulate this level.

Key Points

Normal Range: The typical concentration of Na+ in blood (serum sodium) is 135–145 mmol/L, a tight range essential for health.
Fluid Balance: Sodium's primary role is to regulate the body's fluid balance, impacting blood volume and blood pressure.
Nerve and Muscle Function: Sodium is crucial for the electrical signaling needed for nerve impulses and muscle contractions, including the heart.
Hyponatremia (Low Sodium): Levels below 135 mmol/L can cause nausea, confusion, and fatigue, and in severe cases, seizures or coma.
Hypernatremia (High Sodium): Levels above 145 mmol/L can cause excessive thirst, confusion, and muscle twitching, and in severe cases, brain injury.
Regulation The kidneys, aided by hormones like aldosterone and ADH, are responsible for regulating sodium levels by controlling excretion and reabsorption.
Medical Monitoring: People with chronic illnesses, older adults, and those on certain medications often require regular monitoring of blood sodium levels.

The Importance of Sodium (Na+) in the Body

Sodium is a fundamental electrolyte playing a crucial role in maintaining overall health. As the most abundant cation in the extracellular fluid, it is essential for regulating the body's fluid balance, which in turn affects blood volume and pressure. Beyond fluid regulation, sodium is indispensable for nerve impulse transmission and proper muscle function, including heart muscle contraction. Any deviation from the normal concentration of Na+ in blood can disrupt these processes and indicate an underlying health issue.

Regulation of Blood Sodium Concentration

The concentration of Na+ in blood is a carefully managed process known as sodium homeostasis. The kidneys are the primary organs responsible for this regulation, adjusting the amount of sodium excreted or reabsorbed in the urine. This renal control is orchestrated by a complex interplay of hormones. The renin-angiotensin-aldosterone system (RAAS) is particularly influential. When blood volume or blood pressure decreases, the kidneys release renin, which triggers a cascade leading to the production of aldosterone. Aldosterone signals the kidneys to increase sodium reabsorption, conserving water and raising blood volume. Conversely, when blood volume is high, the heart releases atrial natriuretic peptide (ANP), which promotes sodium excretion to lower blood volume and pressure. Another key hormone, antidiuretic hormone (ADH), also helps regulate water balance, which directly affects sodium concentration.

What are normal blood sodium levels?

The normal range for the concentration of Na+ in blood is typically cited as 135–145 mmol/L, though slight variations exist between different laboratories. This measurement, referred to as serum sodium, is obtained via a blood test, often as part of a routine electrolyte panel.

Abnormalities in Blood Sodium Concentration

Hyponatremia: Low Blood Sodium

Hyponatremia is the condition where the concentration of Na+ in blood falls below 135 mmol/L. The underlying causes can vary widely, from excessive water intake diluting the blood to conditions that cause sodium loss or fluid retention.

Causes of Hyponatremia
- Overhydration (e.g., drinking excessive amounts of water, especially during endurance sports)
- Diuretics (water pills) and certain antidepressants
- Heart, liver, or kidney problems
- Severe vomiting or diarrhea
- Hormonal changes, such as Addison's disease or SIADH
Symptoms of Hyponatremia
- Nausea and vomiting
- Headache and confusion
- Fatigue and lethargy
- Muscle cramps or weakness
- In severe cases, seizures, coma, or brain swelling can occur

Hypernatremia: High Blood Sodium

Hypernatremia occurs when the concentration of Na+ in blood exceeds 145 mmol/L. It typically results from a water deficit relative to the body's sodium content.

Causes of Hypernatremia
- Dehydration due to insufficient fluid intake
- Excessive fluid loss from sweating, vomiting, or diarrhea
- Diabetes insipidus, which causes excessive urination
- Certain medications, including corticosteroids
- Impaired thirst mechanism, especially in older adults
Symptoms of Hypernatremia
- Excessive thirst
- Confusion and irritability
- Fatigue and weakness
- Muscle twitching and seizures
- In severe cases, can lead to brain injury or coma

Comparison of Sodium Imbalances


Feature	Hyponatremia	Hypernatremia
Serum Sodium Level	< 135 mmol/L	> 145 mmol/L
Underlying Problem	Excess body water relative to sodium; can be caused by fluid overload or sodium loss	Water deficit relative to body sodium
Primary Causes	Diuretics, heart/kidney/liver disease, overhydration	Dehydration, diabetes insipidus, excessive fluid loss
Common Symptoms	Nausea, confusion, headache, muscle cramps	Excessive thirst, fatigue, confusion, muscle twitching
Severe Complications	Seizures, coma, brain swelling	Seizures, coma, brain hemorrhage
Treatment	Depends on cause; may include fluid restriction or IV fluids	Increasing fluid intake, often via IV fluids

Clinical Implications and Management

Diagnosing an abnormal concentration of Na+ in blood involves a simple blood test. A doctor will interpret the results in the context of the patient's symptoms, medical history, and other lab findings. Treatment strategies vary depending on the severity and underlying cause. For instance, mild hyponatremia might be managed with fluid restriction, while severe cases may require intravenous sodium solutions. Similarly, treating hypernatremia involves restoring fluid balance, often with IV fluids. It's crucial to correct chronic imbalances gradually to prevent serious complications like osmotic demyelination syndrome in hyponatremia and cerebral edema in hypernatremia. Ongoing monitoring is essential, especially for individuals with chronic conditions or those on specific medications that affect fluid and electrolyte balance.

Conclusion

The concentration of Na+ in blood is a vital marker of overall health, with a normal range of 135–145 mmol/L. This concentration is meticulously maintained by the body's kidneys and hormonal systems to support critical functions like fluid balance, nerve signaling, and muscle contraction. Deviations from this narrow range, whether low (hyponatremia) or high (hypernatremia), can indicate serious health problems and cause a range of symptoms. Accurate diagnosis through blood testing and appropriate, often gradual, medical intervention are necessary to restore balance and prevent life-threatening complications.

For more comprehensive medical information, consult a resource like the MSD Manuals.

Frequently Asked Questions

A blood sodium test measures the concentration of sodium in your blood (serum sodium). It is used to check your body's fluid and electrolyte balance and can help diagnose various health conditions.

The primary cause of low sodium (hyponatremia) can be either excessive fluid retention, which dilutes the sodium, or excessive sodium loss. Causes include certain medications like diuretics, severe vomiting or diarrhea, and conditions affecting the heart, liver, or kidneys.

The main cause of high sodium (hypernatremia) is a lack of sufficient water in the body, leading to dehydration. This can result from inadequate fluid intake, excessive fluid loss (e.g., sweating, diarrhea), or conditions like diabetes insipidus.

The kidneys regulate sodium concentration by adjusting the amount of sodium reabsorbed into the bloodstream or excreted in the urine. This is controlled by hormones like aldosterone and vasopressin (ADH), which are released in response to changes in blood volume or osmolality.

In healthy individuals, high dietary sodium intake is typically managed by the kidneys. However, it can contribute to high blood pressure. High blood sodium (hypernatremia) is usually a result of water imbalance, though excessive sodium intake can be a factor, especially in those with impaired kidney or thirst function.

Symptoms of severely low sodium can be more dramatic and include seizures, loss of consciousness, and coma.

Correction speed depends on the cause and duration of the imbalance. For chronic conditions, a gradual correction is necessary to prevent complications like osmotic demyelination syndrome in hyponatremia or cerebral edema in hypernatremia.