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Sodium concentration in serum/plasma (24-hour fluid collection)

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

This test measures the amount of sodium, an important electrolyte, in your body over a 24-hour period. Sodium helps balance fluids and support nerve and muscle function.

Quick summary

["Understanding your sodium balance over time can help identify fluid shifts or kidney function issues."]

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

Key facts at a glance

LOINC
97780-1
Short code
Sodium 2h spec Dial fld-sCnc
Synonyms
Sodium 2h spec Dial fld-sCnc
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 This Test Is Done

Your doctor may order this test if they suspect you have conditions like dehydration, kidney problems, or excessive fluid retention. It can also help monitor long-term sodium intake, especially in people with heart, kidney, or liver disease.

What to Expect Before the Test

You’ll need to collect urine for 24 hours, starting after you’ve emptied your bladder at the beginning of the period. Drink enough fluids to produce urine throughout the day, but avoid adding extra sodium to your diet during this time.

How the Test Works

The collected urine is sent to a lab where it’s analyzed to determine the total sodium content over the 24-hour period.

Possible Results and Their Meaning

Results may indicate whether your body is retaining or losing sodium too quickly. High sodium levels might suggest dehydration or kidney issues, while low levels could point to conditions like heart failure or excessive vomiting/diarrhea.

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

24-Hour Sodium

Frequently asked questions

How long does it take to get my results?
Results are typically available within 1 to 3 business days, depending on your lab’s processing time.
Can I eat or drink anything special before this test?
No special diet is required, but avoid adding extra salt or sodium-rich foods to your meals during the 24-hour collection period.
What if I miss collecting urine for part of the day?
If you miss any urine collection, your test may not be accurate. Follow your healthcare provider’s instructions to ensure complete collection.
  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