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Serum or Plasma Free Creatinine Concentration (Mass Concentration)

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

This test measures the amount of creatinine, a waste product from muscle metabolism, that is freely present in your blood or plasma without being bound to other substances.

Quick summary

["Assessing your kidney function by checking how well your body removes creatinine from your blood."]

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

Key facts at a glance

LOINC
3231-8
Short code
Fact XII PPP-aCnc
Synonyms
Fact XII PPP-aCnc
Category
chemistry
Sample
plasma
Container
Lavender-top (EDTA) or Green-top (Heparin)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
coag
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 Matters

Creatinine is a byproduct of muscle breakdown and is filtered out by your kidneys. High levels can indicate poor kidney function, while low levels may suggest overhydration or other conditions. This test helps doctors monitor kidney health, especially in people with diabetes, high blood pressure, or other chronic conditions.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to avoid certain medications or supplements that could affect results. If you have kidney disease, your doctor may advise timing your test around a stable hydration level.

What the Results Mean

Results are compared to a general reference range, though individual ranges can vary by lab. Elevated levels may signal kidney problems, while very low levels might need further investigation to rule out dehydration or other factors.

Common Causes of Abnormal Results

High creatinine levels can result from kidney disease, dehydration, or muscle damage. Low levels might be due to overhydration, certain medications, or liver/kidney issues. Your doctor will discuss these with you based on your full medical picture.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Free Creatinine

Frequently asked questions

How often should I get this test?
Your doctor will determine frequency based on your health status. For example, people with kidney disease may need regular monitoring, while others may only need it occasionally.
Does diet affect this test?
Yes, high-protein foods or muscle activity can temporarily raise creatinine levels. Avoiding intense exercise or large protein meals before testing may help stabilize results.
What if my results are out of range?
Your doctor will review your results alongside other tests and your medical history to understand the cause. They may recommend follow-up tests or adjustments to your treatment plan.
  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