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Serum or Plasma Creatinine Concentration (Mass Concentration)

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

This test measures the amount of creatinine, a waste product from muscle metabolism, in your blood or plasma. It helps assess how well your kidneys are filtering blood.

Quick summary

["A key indicator of kidney function and overall kidney health."]

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

Key facts at a glance

LOINC
37784-6
Short code
XR Ribs-R Lat
Synonyms
XR Ribs-R Lat
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
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

What Is Creatinine?

Creatinine is a byproduct of muscle breakdown that your kidneys filter out of your blood. High levels may suggest kidney problems, while low levels could indicate dehydration or muscle loss.

Why Is This Test Done?

Doctors order creatinine tests to monitor kidney function, especially in people with conditions like diabetes, high blood pressure, or those taking medications that affect kidneys. It’s also used before surgeries or when symptoms like swelling, fatigue, or frequent urination appear.

How Is the Test Performed?

A blood sample is taken from a vein, usually in your arm. The sample is sent to a lab where it’s analyzed to measure creatinine levels. Urine tests (like the 24-hour creatinine clearance test) can also be done to assess kidney function indirectly.

What Do Results Mean?

Results alone don’t diagnose kidney disease but help track trends over time. Elevated levels may signal reduced kidney function, while persistently low levels might warrant further investigation for causes like dehydration or muscle disorders.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Creatinine

Frequently asked questions

What causes creatinine levels to change?
Several factors can influence creatinine levels, including muscle mass (higher muscle = higher creatinine), dehydration or fluid overload, certain medications, or kidney disease. Dietary protein intake may also play a role, though it’s less direct than muscle mass.
How often should I get this test?
Frequency depends on your health. People with kidney disease or risk factors (like diabetes or hypertension) may need tests every few months. Others with no known issues may only need baseline tests or occasional follow-ups.
Can diet affect creatinine levels?
Dietary protein intake can influence creatinine levels, but the effect is indirect. High protein intake may temporarily raise creatinine, but long-term changes depend more on kidney function and muscle mass than food alone.
  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