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Serum/plasma sodium concentration (electrolyte measurement)

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

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

Quick summary

["Sodium levels help doctors check for dehydration, kidney issues, or other health concerns."]

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

Key facts at a glance

LOINC
33299-9
Short code
N-Ac-L-Asp Ur Ql
Synonyms
N-Ac-L-Asp Ur Ql
Category
chemistry
Sample
urine
Container
Sterile urine container
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your doctor may order this test to diagnose or monitor conditions like high blood pressure, kidney disease, heart problems, or electrolyte imbalances. It’s also used to check for dehydration, excessive sweating, or improper hormone function.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for a few hours if your blood is drawn early in the morning. Wear comfortable clothing and plan to stay for about 15 minutes while the blood is drawn.

What Happens During the Test?

A healthcare professional will insert a small needle into a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause pain. Blood is collected into a tube, and the needle is removed. The process takes a few minutes.

What Happens After the Test?

You can resume normal activities immediately. Apply gentle pressure to the site to stop any bleeding, and avoid rubbing it. If you experience dizziness or fainting, lie down and rest for a few minutes.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Low sodium levels (hyponatremia) can cause headaches, confusion, nausea, or muscle cramps. High sodium levels (hypernatremia) may lead to thirst, dry mouth, or irregular heartbeat. Both extremes can affect how your body regulates fluids and nerves. Your doctor will use this test result along with other factors to guide treatment.

Short name

Sodium level

Frequently asked questions

What causes sodium levels to change?
Sodium levels can be affected by dehydration (losing too much water), kidney problems, excessive sweating, vomiting, or certain medications. Conditions like heart failure or liver disease may also influence sodium balance.
How long does it take to get results?
Results are typically available within 24 hours, depending on your lab’s processing time. Your doctor will contact you with the results once they are ready.
Can I eat or drink before this test?
No special diet is required, but if your blood is drawn early in the morning, you may need to fast for a few hours before the test.
  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