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Serum/plasma mass concentration of sodium

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

This test measures the amount of sodium, a key mineral, in your blood plasma or serum. Sodium helps regulate fluid balance and nerve/muscle 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 17, 2026Editorial policy

Key facts at a glance

LOINC
23922-8
Short code
OF .85% NaCl NFr RBC
Synonyms
OF .85% 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 This Test Matters

Sodium is essential for maintaining proper fluid balance in your body. Too little or too much can lead to serious health issues, such as swelling, high blood pressure, or heart problems. Your doctor may order this test if you have symptoms like confusion, excessive thirst, or swelling in your legs or ankles.

What to Expect Before the Test

No special preparation is needed for this test. You’ll have a small needle inserted into your arm or vein to draw blood. If you’re having a 24-hour urine test for sodium, you’ll need to collect all urine for a full day, starting after your first morning urine.

What the Results Mean

Results are compared to standard ranges for healthy adults. Low sodium (hyponatremia) or high sodium (hypernatremia) can indicate conditions like kidney problems, heart failure, or excessive sweating.

Common Causes of Abnormal Results

Changes in sodium levels can stem from dehydration, kidney disease, heart problems, or certain medications. Your doctor will review your symptoms and other test results to determine the cause.

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.

◆Associated findings1

Short name

Sodium level

Frequently asked questions

How long does it take to get sodium test results?
Results are typically available within 1 to 3 business days, depending on your lab. If your test is part of a more complex evaluation, results may take longer.
Can I eat or drink before a sodium blood test?
For a blood sodium test, you can eat and drink normally. For a 24-hour urine sodium test, avoid excessive salt intake and follow your doctor’s instructions for proper urine collection.
What should I do if my sodium level is too high or too low?
Contact your doctor immediately if you experience symptoms like confusion, nausea, muscle cramps, or swelling. They’ll guide you on next steps, which may include lifestyle changes or medical treatment.
  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