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Sodium (Serum) Concentration

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of sodium, a key electrolyte, in your blood serum. Sodium helps balance fluids and maintain proper nerve and muscle function.

Quick summary

["Your sodium levels help doctors check for dehydration, kidney issues, or other health conditions."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
82812-9
Short code
Sodium RBC-mCnc
Synonyms
Sodium RBC-mCnc
Category
electrolyte
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Ref low
136
Ref high
145
Critical range
120 N/A – 160 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84295
SNOMED
110741000
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Doctors may order a serum sodium test to diagnose or monitor conditions like dehydration, kidney disease, heart problems, or hormonal imbalances. It’s also used to check for high or low sodium levels that could affect your body’s ability to regulate fluids and electrolytes.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into your arm to draw blood. If you’re on a fluid restriction, follow your doctor’s instructions carefully. Avoid eating or drinking anything (except water) for at least 8–12 hours before the test if specified.

What Happens During the Test?

Blood is drawn from a vein in your arm and sent to a lab for analysis. The test usually takes a few minutes, and you may feel a brief pinch or discomfort during the draw. The results are typically ready within 24 hours.

What the Results Mean

Results are compared to a standard range, but exact values can vary by lab. Low sodium (hyponatremia) may cause headaches, confusion, or muscle cramps, while high sodium (hypernatremia) could lead to thirst, fatigue, or irregular heartbeat. Your doctor will discuss your specific results and next steps.

Reference range

Adult: 136-145 mmol/LN/A

Specimen: whole-blood

No special preparation required. Stay well hydrated.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Serum Sodium

Frequently asked questions

What Causes Abnormal Sodium Levels?
Abnormally low sodium can result from excessive fluid loss (e.g., vomiting, diarrhea), kidney problems, or conditions like heart failure or syndrome of inappropriate antidiuretic hormone (SIADH). High sodium levels may occur from dehydration, excessive salt intake, or hormonal imbalances like diabetes insipidus.
How Are Sodium Levels Treated?
Treatment depends on whether sodium is too high or too low. For hyponatremia, doctors may adjust fluid intake or medications to reduce sodium loss. For hypernatremia, they might encourage more fluids or restrict salt. Lifestyle changes, like reducing salt or managing underlying conditions, are often part of the plan.
Can I Avoid This Test?
No, this test is essential for diagnosing and managing conditions related to electrolyte imbalances. Your doctor may recommend it if you have symptoms or risk factors for sodium-related issues.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy