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Sodium concentration in plasma or serum

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

This test measures the amount of sodium, a key mineral electrolyte, in your blood plasma or serum. Sodium helps regulate fluid balance, nerve and muscle function, and blood pressure.

Quick summary

["Sodium levels help doctors check for dehydration, kidney issues, or conditions like high blood pressure."]

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

Key facts at a glance

LOINC
9485-4
Short code
Sodium Wat-mCnc
Synonyms
Sodium Wat-mCnc
Category
electrolyte
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
136
Ref high
145
Critical range
120 N/A – 160 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84295
SNOMED
110741000
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 if you have symptoms like excessive thirst, confusion, muscle cramps, or unexplained swelling. It’s also used to monitor conditions like heart failure, kidney disease, or hormonal imbalances that affect sodium levels.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before testing if your doctor specifies. Bring any medications you’re taking, as some can affect sodium levels.

How the Test Works

A blood sample is drawn from a vein, usually in your arm. The sample is sent to a lab where sodium concentration is measured using a specialized instrument that detects the mineral’s presence.

What the Results Mean

Results are compared to a reference range provided by your lab. Low sodium (hyponatremia) or high sodium (hypernatremia) can signal underlying health concerns, but exact values depend on your health status and other factors.

Reference range

Adult: 136-145 mmol/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

What causes sodium levels to be too low?
Low sodium can result from excessive fluid loss (e.g., vomiting, diarrhea), kidney problems, or conditions like heart failure or syndrome of inappropriate antidiuretic hormone (SIADH). Lifestyle factors, such as overuse of salt substitutes or certain medications, may also play a role.
What causes sodium levels to be too high?
High sodium often occurs from dehydration, excessive salt intake, or conditions like diabetes insipidus or kidney disease. Rarely, it can be caused by hormonal imbalances or certain medications.
How often should I get this test?
Your doctor will determine how often you need this test based on your health history, symptoms, and treatment plan. Regular monitoring may be needed if you have chronic conditions like kidney disease or heart failure.
  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