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Serum or Plasma Free Fraction of Creatinine (or Protein-bound Creatinine Ratio)

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

This test measures how much of the creatinine in your blood is unbound (free) versus bound to proteins. It helps assess kidney function and protein binding dynamics.

Quick summary

["Understanding how creatinine binds to proteins in your blood can aid kidney health evaluation."]

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

Key facts at a glance

LOINC
24695-9
Short code
XR Face Views
Synonyms
XR Face Views
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
xr
CPT
86430
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 healthcare provider may order this test if they suspect kidney issues, evaluate protein-related conditions, or monitor medications that rely on protein binding. It can also help assess how well your kidneys filter waste products when other tests are inconclusive.

What to Expect Before the Test

No special preparation is needed. You’ll provide a blood sample, typically drawn from a vein in your arm. If you’re on certain medications, inform your provider beforehand to ensure accurate results.

What the Results Mean

Results compare the unbound (free) portion of creatinine to the total creatinine in your blood. Lower free fraction may indicate conditions like kidney disease or protein overload, while higher values could suggest protein deficiency or altered kidney function.

Common Conditions Monitored

This test supports diagnosis or management of kidney disorders, protein-related diseases (e.g., liver or kidney disease), and conditions affecting protein binding (e.g., malnutrition or severe infections).

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Creatinine Ratio

Frequently asked questions

What does a ‘free creatinine ratio’ test tell me about my kidney health?
It helps assess how much of your creatinine is unbound, which can indicate kidney function or protein-binding issues. While not a standalone kidney test, it may complement other evaluations for conditions like kidney disease or protein disorders.
Why would my doctor ask for this test?
Your doctor may request it if they suspect kidney problems, monitor medications that depend on protein binding, or investigate conditions affecting protein levels (e.g., liver disease, malnutrition). It’s also used in research or specialized cases where creatinine binding dynamics are critical.
Is fasting required for this test?
No fasting is needed. Blood is drawn at any time of day, similar to standard blood tests. However, inform your provider about any medications or conditions that could affect 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