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Serum Creatinine (with optional 24-hour urine collection for calculation)

Published: August 9, 2026Updated: August 17, 2026

This test measures the amount of creatinine, a waste product from muscle metabolism, in your blood or urine to assess kidney function.

Quick summary

["Kidney health check: creatinine helps evaluate how well your kidneys filter blood."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
85378-8
Short code
RBC.EMA MFI Act/Nor Bld FC
Synonyms
RBC.EMA MFI Act/Nor Bld FC
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Ref low
4.2
Ref high
5.9
Critical range
2 N/A – 7 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
flow-cytometry
CPT
85041
SNOMED
900000000000003001
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Matters

Creatinine is a byproduct of muscle breakdown and is naturally filtered by your kidneys. High levels may indicate impaired kidney function, while low levels could suggest overhydration or other conditions. This test is often used alongside other measures to diagnose and monitor kidney disease.

How the Test Works

Your blood or urine sample is analyzed to measure creatinine concentration. If a 24-hour urine collection is requested, you’ll collect all urine over a full day to measure creatinine excretion, which helps calculate kidney function more precisely.

Common Reasons for Testing

Doctors may order this test if you have symptoms like fatigue, swelling, frequent urination, or if you have a history of kidney problems, diabetes, or high blood pressure. It’s also used before surgeries, during pregnancy, or to monitor chronic conditions like heart disease.

What to Expect Before the Test

No special preparation is needed for a blood test, but if you’re collecting urine for 24 hours, keep track of all urine output (excluding toilet waste) in a container. Avoid excessive alcohol or contrast dyes (if prescribed) before urine tests.

Reference range

Adult males: 4.2-5.9; Females: 3.8-5.1 x 10^12/LN/A

Specimen: whole-blood

No special preparation required. Stay well hydrated.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Creatinine Level

Frequently asked questions

What does a high creatinine level mean?
High creatinine levels often signal reduced kidney function, as your kidneys struggle to filter waste effectively. This can be due to kidney disease, dehydration, or conditions like diabetes or heart failure. Your doctor may recommend further testing or adjustments to your treatment plan.
What does a low creatinine level mean?
Low creatinine levels may indicate overhydration, muscle loss, or conditions like liver disease (which affects muscle breakdown). They can also occur in people with very little muscle mass. Always discuss results with your healthcare provider, as they’ll consider your overall health.
Can diet affect creatinine levels?
Yes, diet can influence creatinine levels. High-protein foods or excessive muscle activity may temporarily raise levels, while low-protein diets or muscle loss (e.g., from illness) can lower them. Your doctor may adjust your diet or test timing if needed.
  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 17, 2026. · Read our editorial policy