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Serum Sodium (Electrolyte)

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

This test measures the amount of sodium in your blood, which helps maintain fluid balance and nerve/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 17, 2026Editorial policy

Key facts at a glance

LOINC
52124-5
Short code
OF .90% NaCl NFr RBC
Synonyms
OF .90% 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 diagnose or monitor conditions like dehydration, high blood pressure, kidney disease, or electrolyte imbalances. It’s often checked alongside other electrolytes like potassium and chloride.

What to Expect Before the Test

You’ll typically have a small needle inserted into your arm to draw blood. No special preparation is needed, but avoid heavy meals or excessive fluids 8–12 hours before if instructed.

What the Results Mean

Results are compared to standard ranges, but your doctor will interpret them in the context of your overall health. Low sodium (hyponatremia) may cause headaches or confusion, while high sodium (hypernatremia) could indicate dehydration or kidney problems.

Common Conditions Affecting Sodium Levels

Conditions like heart failure, kidney disease, or excessive sweating (e.g., from heat or exercise) can alter sodium levels. Certain medications (e.g., diuretics) may also impact sodium balance.

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.

Sodium plays a critical role in fluid regulation, nerve signaling, and muscle function. Abnormal levels can lead to serious complications, such as seizures, irregular heart rhythms, or even coma in extreme cases.

Short name

Serum Sodium

Frequently asked questions

What causes sodium levels to be too low or too high?
Low sodium is often due to excessive fluid loss (e.g., vomiting, diarrhea), kidney problems, or conditions like heart or liver disease. High sodium may result from dehydration, kidney failure, or overuse of salt.
How long does it take to get results?
Results are usually available within 1–2 business days, depending on your lab’s processing time. Your doctor will discuss them with you during your follow-up visit.
Can I eat or drink anything before this test?
Most tests don’t require fasting, but follow your doctor’s instructions if they specify restrictions (e.g., no fluids for 8 hours). Always check with your healthcare provider.
  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