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Serum/plasma sodium concentration (mass concentration)

Published: August 9, 2026Updated: August 17, 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 assess hydration, electrolyte balance, and potential health risks like high blood pressure or kidney issues."]

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

Key facts at a glance

LOINC
23913-7
Short code
OF .40% NaCl NFr RBC
Synonyms
OF .40% 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 Sodium Levels Matter

Sodium is a key electrolyte that helps maintain fluid balance in your body. Too much or too little can lead to serious health problems, such as swelling, muscle cramps, or irregular heartbeat. Your doctor may order this test if you have symptoms like excessive thirst, confusion, or unexplained weight changes.

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 on a sodium-restricted diet, your doctor may ask you to follow their instructions for a few days before testing.

Possible Causes of Abnormal Results

High sodium levels (hypernatremia) may occur due to dehydration, kidney problems, or excessive salt intake. Low sodium levels (hyponatremia) can result from excessive sweating, vomiting, diarrhea, or certain medications. Your doctor will review your symptoms and medical history to determine the cause.

What the Results Mean

Your results will be compared to standard reference ranges provided by your lab. While exact values vary by lab, very high or very low sodium levels may trigger further testing or adjustments to your treatment plan.

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

Short name

Sodium Level

Frequently asked questions

How often do I need this test?
This test is often checked periodically if you have conditions like heart disease, kidney problems, or are on certain medications that affect sodium levels. Some people may need it more frequently if they’re hospitalized or managing chronic health issues.
Can diet affect sodium test results?
Yes, your diet can influence sodium levels. Eating too much salt or drinking too little water can raise sodium, while excessive sweating or fluid loss can lower it. Your doctor may ask you to follow a specific diet for a few days before testing to get accurate results.
What should I do if my sodium level is out of range?
If your sodium level is unusually high or low, your doctor will review your results and may recommend changes to your diet, medications, or fluid intake. In severe cases, they might suggest additional tests or treatments to stabilize your levels safely.
  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