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Serum or plasma sodium concentration (electrolyte measurement)

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

This test measures the amount of sodium in your blood, an important electrolyte that helps balance fluids and maintain nerve and muscle function.

Quick summary

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

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

Key facts at a glance

LOINC
30913-8
Short code
S Phs Cells NFr Spec FC
Synonyms
S Phs Cells NFr Spec FC
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
flow-cytometry
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 Sodium Levels Matter

Sodium is vital for keeping your body’s fluids balanced, supporting nerve signals, and helping muscles work properly. Too much or too little can lead to serious health problems, like high blood pressure or swelling.

What Can Affect Your Sodium Level?

Several factors can influence sodium levels, including diet (especially salty foods), kidney function, dehydration, or certain medications. Stress, illness, or even extreme exercise can also play a role.

Common Causes of Abnormal Results

High sodium levels (hypernatremia) may occur if you lose too much water (e.g., from vomiting or diarrhea) or if your body retains too much sodium. Low sodium levels (hyponatremia) can happen if you drink too much water, have kidney problems, or lose sodium through sweat or medications.

What to Expect During the Test

A simple blood draw is used to collect a small sample from your arm. The lab will then analyze the sodium content in your serum or plasma. This test is quick and usually painless, with minimal recovery time needed.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Sodium Level

Frequently asked questions

How is this test used in diagnosis?
Doctors use sodium levels to diagnose or monitor conditions like dehydration, kidney disease, heart problems, or hormonal imbalances. Frequent checks may also be needed if you have chronic health issues like high blood pressure or diabetes.
What does a low sodium level mean?
A low sodium level may signal conditions like excessive water intake, kidney dysfunction, or certain medications (like diuretics). It can cause symptoms like headaches, confusion, or muscle cramps.
What does a high sodium level mean?
A high sodium level might indicate dehydration, excessive salt intake, or conditions like hyperaldosteronism. Symptoms can include thirst, fatigue, or swelling in the legs.
  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