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Serum or Plasma Sodium (Electrolyte Concentration)

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

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

Quick summary

["Sodium helps regulate fluid balance and nerve function; low or high levels can cause serious health issues."]

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

Key facts at a glance

LOINC
23911-1
Short code
OF .30% NaCl NFr RBC
Synonyms
OF .30% NaCl NFr RBC
Category
electrolyte
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
4.2
Ref high
5.9
Critical range
2 N/A – 7 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
85041
SNOMED
900000000000003001
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 check for conditions like dehydration, kidney problems, heart disease, or hormonal imbalances. It’s also used to monitor treatments for conditions such as hypertension or diabetes.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into your arm or vein to draw blood. If you’re on a sodium-restricted diet, let your doctor know before testing.

What the Results Mean

Results are compared to a standard range for healthy adults. Very high or very low sodium levels can indicate underlying health concerns that need attention.

Common Conditions Linked to Sodium Levels

Abnormally high sodium (hypernatremia) may result from dehydration, excessive salt intake, or kidney issues. Abnormally low sodium (hyponatremia) can stem from fluid overload, kidney problems, or certain medications.

Reference range

Adult males: 4.2-5.9; Females: 3.8-5.1 x 10^12/LN/A

Specimen: serum

No special preparation required. Stay well hydrated.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Sodium Levels Are Critical for Health

Short name

Sodium Level

Frequently asked questions

How often will I need this test?
The frequency depends on your health condition and treatment plan. Your doctor will determine how often to check your sodium levels based on your needs.
What are the typical reference ranges for sodium?
Reference ranges vary by lab and may differ slightly between serum and plasma. Generally, healthy adults have sodium levels between 135 and 145 milliequivalents per liter (mEq/L). Your doctor will provide your specific results.
Can I eat or drink anything before this test?
You can eat and drink normally unless your doctor specifies otherwise. Avoid excessive salt intake or fluids if instructed, as it may affect your sodium level.
  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