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Total Fat-Free Mass in 24-Hour Urine Collection (measured as mass concentration)

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

This test measures the amount of fat-free material excreted in your urine over a 24-hour period. It helps assess kidney function and how well your body filters waste products.

Quick summary

["This test helps doctors evaluate kidney health and metabolic processes by tracking waste removal over a full day’s urine output."]

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

Key facts at a glance

LOINC
34329-3
Short code
Fat 24h Stl-mCnt
Synonyms
Fat 24h Stl-mCnt
Category
chemistry
Sample
stool
Container
Clean container
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 they suspect kidney disease, metabolic disorders, or conditions affecting fluid and electrolyte balance. It can also be used to monitor long-term kidney function in certain chronic conditions.

What to Expect Before the Test

You’ll need to collect all your urine for 24 hours, typically starting after midnight on one day and ending the same time the next day. Follow your doctor’s instructions carefully to ensure accurate results.

How the Test Works

The test measures the total fat-free mass in your urine, which includes substances like urea, creatinine, and other waste products. This helps determine how efficiently your kidneys filter these substances from your blood.

What the Results Mean

Higher-than-expected results may indicate kidney problems, metabolic disorders, or excessive fluid loss. Lower-than-expected results could suggest dehydration or impaired kidney function. Your doctor will interpret the results in the context of your overall health.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

24-Hour Fat-Free Mass Urine Test

Frequently asked questions

How long does it take to get my results?
Results are typically available within 1 to 2 weeks after your lab receives the urine sample. Your doctor will contact you once they have the final report.
Can I eat or drink normally before this test?
Yes, you can eat and drink as usual, but avoid excessive caffeine or alcohol, as they may affect urine composition. Follow your doctor’s specific instructions for any dietary restrictions.
Will I need to fast before this test?
No fasting is required for this test. The 24-hour urine collection must be completed over a full day, but you can eat and drink normally throughout the process.
  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