CMP Updated Apr 17, 2026

Sodium (Na)

Sodium (Na) is a lab value that measures the amount of sodium in blood, usually reported in mmol/L. Sodium on a blood test helps show how concentrated the blood sample is and how water balance is reflected in the result. On a metabolic panel, Na is read alongside other chemistry markers to describe the overall composition of the blood sample.

What Is Sodium (Na)?

Sodium (Na) is a blood chemistry value that measures the amount of sodium in the sample. It is part of the body’s main fluid balance system and is usually reported in mmol/L. Sodium on a blood test reflects how concentrated the blood sample is and how water shifts can change the Na test result.

Why Is Sodium (Na) Tested?

Na is commonly included in a metabolic panel, especially a comprehensive metabolic panel (CMP) or basic metabolic panel (BMP). It is also measured in some routine blood checkups and during follow-up lab work where the fluid and electrolyte pattern is being reviewed. Sodium on a lab report helps show the broader chemistry pattern alongside other markers.

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Sodium (Na) Normal Range

Group Range Unit
Adult Male 135–145 mmol/L
Adult Female 135–145 mmol/L

Reference ranges may vary by laboratory and individual factors.

What Does High Na Mean?

A high Na test result generally means the sodium concentration in blood is above the Sodium normal range, often above about 145 mmol/L in adults. High Na usually reflects a more concentrated blood sample, often because water is lower relative to sodium. A high Sodium test result does not describe body sodium stores by itself; it describes the measured concentration in the sample.

Associated factors

Dehydration — reduced water in the sample concentrates Na and raises the measured value.
Heavy sweating — fluid loss through sweat can make blood sodium more concentrated.
Low fluid intake — less water intake can increase concentration on a Sodium test.
Diuretic use — increased urine loss can reduce plasma volume and raise Na.
High salt intake — a large sodium load can raise measured Na in some settings.
GI fluid shifts — fluid loss can concentrate the blood sample and increase high Na.
Exercise — prolonged activity can shift water balance and change Na on a blood test.
Older age — age-related changes in water balance can slightly affect Na results.
Pregnancy — plasma volume changes can alter how Na appears on a lab report.
Smoking — can be associated with small shifts in fluid balance that influence Na.

What Does Low Na Mean?

A low Na test result generally means the sodium concentration is below the Sodium normal range, often below about 135 mmol/L in adults. Low Na usually reflects a less concentrated blood sample, often because water is higher relative to sodium. A low Sodium test result describes the measured concentration in the blood sample, not total body sodium stores.

Associated factors

High fluid intake — extra water can dilute Na and lower the measured value.
Fluid retention — increased body water can make Na appear low on a blood test.
Diuretic use — some medicines can change water and sodium handling and lower Na.
GI fluid shifts — sodium loss can reduce the measured concentration.
Sweating with water replacement — replacing only water can dilute Na.
Endurance exercise — large fluid shifts can lower Na on a blood test.
Low dietary intake — limited sodium intake can contribute to a low Na result.
Older age — changes in water handling can make low Na more likely on labs.
Pregnancy — expanded plasma volume can lower the measured concentration.
Certain hormone medicines — medicines that affect water balance can lower Na.

How Sodium (Na) Relates to Other Values

Na is often read with chloride (Cl), potassium (K), and carbon dioxide (CO2) on a metabolic panel. These markers help describe how dissolved minerals and acid-base balance are distributed in the blood sample. Na on a lab report is also interpreted with blood urea nitrogen (BUN) and creatinine when the goal is to see the broader chemistry pattern. Compared with hematocrit (Hct), red blood cell count (RBC), and mean corpuscular volume (MCV), Na reflects fluid chemistry rather than red cell size or number.

What Factors Affect Sodium (Na) Levels?

Age, sex, hydration, diet, and recent exercise can all influence Na on a blood test. Altitude and sweating can change fluid balance and shift the measured concentration. Pregnancy can lower the apparent concentration because of higher blood volume. Different lab methods may produce small variation, so the Sodium normal range can vary slightly by lab. Ethnicity is not a major direct driver of Na, but diet patterns and environment can influence the result indirectly.

How It Is Tested

Na is measured from a blood draw, usually from a vein in the arm. The lab analyzes the sodium concentration in the sample and reports the Na test result most often in mmol/L. Some labs may also show sodium in mEq/L, which is numerically the same for Na in this context.

How to Prepare

No fasting is usually required for a Sodium test as part of a metabolic panel. The sample timing and recent fluid intake can still affect how Na appears on the report.

Frequently Asked Questions

What is the normal range for Sodium?
The Sodium normal range in many US labs is about 135 to 145 mmol/L for adults. Na can vary a little by lab, so the reference interval on the report is the best match for that test. A Sodium on a lab report value inside that range is usually considered typical for the sample.
What does Na stand for in a blood test?
Na stands for Sodium. On a blood test, Na is the shorthand used for the sodium concentration in the sample. It is commonly shown on a metabolic panel and may also appear as Sodium on a lab report.
What does a high Sodium mean on a lab report?
A high Na usually means the blood sample is more concentrated than typical, often because water is lower relative to sodium. Values above about 145 mmol/L are often considered high, depending on the lab. This is why a high Na is read as a concentration change on the Sodium test result.
What does a low Sodium mean on a lab report?
A low Na usually means the blood sample is more diluted than typical, often because water is higher relative to sodium. Values below about 135 mmol/L are often considered low in adult reference ranges. A low Na on a blood test is a concentration finding, not a measure of total body sodium alone.
Can hydration affect Sodium?
Yes, hydration can affect Na because blood sodium is reported as a concentration. Extra water can make a Sodium test result look lower, while fluid loss can make it look higher. This is one reason Na on a lab report is interpreted with recent fluid intake in mind.
What is the difference between Sodium and chloride?
Sodium (Na) and chloride (Cl) are both measured on a metabolic panel, but they are different minerals with different roles in blood chemistry. Na is the main positive mineral in the fluid outside cells, while chloride is the main negative one. They are often reviewed together because changes in one can track with changes in the other.
What unit is Sodium measured in?
Na is usually measured in mmol/L. Some labs may use mEq/L, but for Sodium the number is typically the same. The unit on the lab report is important because it shows how the Sodium test result is scaled.
How much can Sodium change between tests?
Na usually changes only a little from one routine test to the next if conditions are similar. Small shifts in hydration, exercise, or timing can move the result by a few mmol/L. Larger changes in the Sodium test result often reflect a bigger shift in fluid balance.
Is Sodium different for men and women?
In most adult reference ranges, Na is not meaningfully different for men and women. Many labs use the same Sodium normal range for both groups, such as 135 to 145 mmol/L. Any small differences are usually due to lab-specific reference intervals rather than sex alone.
Why is Sodium tested in a metabolic panel?
Na is included in a metabolic panel because it helps describe the blood’s fluid and electrolyte pattern. It is read with markers like potassium, chloride, and carbon dioxide to show how the sample is balanced. On a blood test, Na gives context for the rest of the chemistry panel.

Disclaimer

This content is for informational and educational purposes only. It is not intended as medical advice, diagnosis, or treatment recommendation. Reference ranges may vary by laboratory. Always discuss your results with a qualified healthcare professional.

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