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Serum or Plasma Sodium (Electrolyte Concentration)

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

This test measures the amount of sodium in your blood, which helps regulate fluid balance, blood pressure, and nerve/muscle function.

Quick summary

["Sodium levels help doctors check for dehydration, kidney issues, or conditions affecting fluid balance."]

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

Key facts at a glance

LOINC
29796-0
Short code
SLEV NAb Titr CSF Nt
Synonyms
SLEV NAb Titr CSF Nt
Category
chemistry
Sample
csf
Container
Sterile tube
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
neut
Specimen volume
1-2 mL
Stability
Immediate analysis required, Refrigerated: 1h
Hemolysis max
200
TAT
4–24 hours
Order
routine

What Is Sodium’s Role in Your Body?

Sodium is a key electrolyte that helps maintain fluid balance, supports nerve and muscle function, and regulates blood pressure. Low or high sodium levels can lead to symptoms like confusion, muscle cramps, or irregular heartbeat.

When Might You Need This Test?

Your doctor may order a sodium test if you have symptoms like excessive thirst, swelling, confusion, or if you’re taking medications that affect fluid balance (e.g., diuretics). It’s also checked during kidney function evaluations or after illness (e.g., vomiting, diarrhea).

What to Expect Before the Test

No special preparation is needed, but avoid drinking extra fluids on the day of testing if your doctor advises it. Bring any medications you’re taking to your appointment.

What Happens During the Test?

A small blood sample is drawn from a vein, usually in your arm. The sample is sent to a lab for analysis. Results are typically ready within 1–2 days.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Sodium Level

Frequently asked questions

Why might my sodium level be checked repeatedly?
Your sodium level may be monitored closely if you have chronic conditions like heart failure, kidney disease, or liver problems, or if you’re on long-term medications that affect sodium balance. Frequent checks help doctors adjust treatments to prevent dangerous imbalances.
What causes low sodium levels (hyponatremia)?
Low sodium can result from excessive fluid loss (e.g., vomiting, diarrhea), kidney issues, certain medications (like diuretics), or conditions like heart failure or liver disease that cause fluid retention. Symptoms may include headaches, nausea, or weakness.
What causes high sodium levels (hypernatremia)?
High sodium is often linked to dehydration, excessive salt intake, or conditions like diabetes insipidus or kidney problems that reduce fluid retention. Symptoms may include thirst, dry mouth, confusion, or muscle spasms.
  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