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Serum or plasma concentration of sodium (electrolyte)

Published: August 9, 2026Updated: August 17, 2026

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

Quick summary

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

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
103021-2
Short code
S aureus TSST-1 IgE RAST
Synonyms
S aureus TSST-1 IgE RAST
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
— – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
rast
CPT
84484
SNOMED
302774002
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your healthcare provider may order a sodium test to diagnose or monitor conditions like dehydration (from vomiting, diarrhea, or excessive sweating), kidney disease, heart problems, or hormonal imbalances. It’s also used to check for high blood pressure or electrolyte disturbances.

What to Expect Before the Test

No special preparation is needed. You may drink water before the test, but avoid eating or drinking anything for 4–6 hours if instructed. Bring any medications you’re taking, as some can affect results.

What Happens During the Test?

A healthcare professional will draw blood from a vein in your arm. You may feel a slight pinch, but it’s usually over quickly. The blood is sent to a lab for analysis.

What the Results Mean

Results are compared to a standard range, but exact values can vary by lab. Low sodium (hyponatremia) may cause headaches or confusion, while high sodium (hypernatremia) could lead to dry mouth or rapid heartbeat. Your doctor will discuss your specific results with you.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Sodium level

Frequently asked questions

What Are Common Causes of Abnormal Results?
Low sodium levels (hyponatremia) can result from excessive sweating, kidney problems, heart failure, or certain medications (e.g., diuretics). High sodium levels (hypernatremia) may occur from dehydration, kidney disease, or overuse of salt.
How Often Should I Get This Test?
Your doctor will determine how often you need this test based on your health condition. Regular monitoring may be needed if you have chronic kidney disease, heart failure, or take medications that affect sodium levels.
Can I Avoid This Test?
No, this test is essential for diagnosing and managing conditions affecting sodium balance. If you have concerns, discuss them with your doctor to explore alternatives or adjustments to your care plan.
  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 17, 2026. · Read our editorial policy