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Sodium concentration in serum/plasma measured over a 72-hour period (24-hour urine collection)

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

This test measures how much sodium your body loses through urine over 72 hours, helping assess kidney function and fluid balance.

Quick summary

["Understanding your sodium loss helps doctors check if your kidneys are working properly or if you’re retaining too much fluid."]

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

Key facts at a glance

LOINC
2953-8
Short code
Sodium 72h sub Stl Qn
Synonyms
Sodium 72h sub Stl Qn
Category
electrolyte
Sample
stool
Container
Clean container
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 g
Stability
Refrigerated: 24h, Frozen: 7d
TAT
4–24 hours
Order
routine

Why This Test Is Done

Your doctor may order this test if you have symptoms like swelling, high blood pressure, or signs of kidney problems. It helps track how well your body is handling sodium, especially in people with chronic kidney disease or heart conditions.

What to Expect Before the Test

You’ll need to collect all urine for 72 hours in a special container. Drink enough fluids to produce urine consistently, but avoid adding extra sodium to your diet during this time.

How the Test Works

The collected urine is sent to a lab where sodium levels are measured. The test compares your sodium loss to what’s expected, helping identify imbalances.

What the Results Mean

High sodium loss may indicate kidney issues or excessive sweating, while very low loss could signal fluid retention or kidney problems. Your doctor will interpret results based on your health history.

Reference range

Adult: 136-145 mmol/LN/A

Specimen: stool

No special preparation required. Stay well hydrated.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Frequently asked questions

How long will I need to collect urine for this test?
You’ll need to collect all urine for a full 72-hour period, starting and ending at the same time each day. Your doctor or lab will provide detailed instructions.
Can I take medications or eat certain foods during urine collection?
Avoid adding extra sodium to your diet during the collection period. Some medications may affect results, so check with your doctor before starting the test.
What if I miss some urine during the 72-hour period?
If you miss urine, you may need to restart the collection. Inform your lab immediately to avoid inaccurate results.
  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