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Serum or Plasma Sodium Concentration

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

This test measures the amount of sodium in your blood serum or plasma. Sodium is an essential electrolyte that helps maintain fluid balance and nerve function.

Quick summary

["Sodium levels help doctors check if your body is retaining or losing too much fluid or salt."]

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

Key facts at a glance

LOINC
3160-9
Short code
Specimen vol Smn
Synonyms
Specimen vol Smn
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 doctor may order this test to diagnose or monitor conditions like dehydration, kidney problems, heart disease, or high blood pressure. It can also help identify imbalances caused by certain medications or medical treatments.

What to Expect Before the Test

You may be asked to fast for a few hours before the test, depending on your doctor’s instructions. Bring any medications you’re currently taking. Avoid eating or drinking anything except water for the specified period if fasting is required.

How the Test Is Performed

A healthcare professional will draw blood from a vein in your arm using a small needle. You may feel a slight pinch, but it usually doesn’t cause discomfort. The blood sample is then sent to a lab for analysis.

What the Results Mean

Results are typically reported in milliequivalents per liter (mEq/L). Low sodium levels (hyponatremia) can cause headaches, confusion, or muscle cramps, while high sodium levels (hypernatremia) may lead to thirst, fatigue, or irregular heartbeat. Your doctor will interpret the results in the context of your overall health and symptoms.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Sodium Level

Frequently asked questions

How does sodium imbalance affect my health?
Sodium imbalances can lead to serious health issues, such as seizures, coma, or even heart failure in severe cases. Sodium helps regulate fluid balance, nerve signals, and muscle contractions. Chronic imbalances may also indicate underlying conditions like kidney disease, adrenal disorders, or excessive sweating.
What causes sodium levels to change?
Sodium levels can drop due to excessive vomiting, diarrhea, diuretics, or kidney problems. They may rise from dehydration, high salt intake, or conditions like diabetes insipidus or excessive sweating without adequate fluid replacement.
Can I adjust my sodium intake based on my test results?
No, you should not modify your diet or medication based solely on lab results without consulting your doctor. Sodium levels fluctuate based on many factors, including diet, hydration, and medical treatments. Your doctor will guide you on any necessary lifestyle or treatment changes.
  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