C-reactive protein, serum concentration
This test measures the level of C-reactive protein in your blood, a protein produced by your liver in response to inflammation or infection.
["CRP helps track inflammation, often used to check for infections, autoimmune conditions, or other health issues."]
Key facts at a glance
- LOINC
- 24474-9
- Short code
- CAS
- Synonyms
- CASA Ser-aCnc
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) — red-top or gold-top vacutainer tube; alternatively, plain red-top tube without anticoagulant
- Units
- N/A
- Ref low
- 19
- Ref high
- 9
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- Immunoassay (e.g., ELISA, chemiluminescent immunoassay, or radioimmunoassay depending on specific cancer-associated antigen being measured)
- Specimen volume
- 1-3 mL of serum (minimum 0.5 mL); volume requirements vary by assay and number of analytes ordered
- Stability
- Serum is generally stable for 24 hours at room temperature (2-8°C), up to 7 days refrigerated at 2-8°C, and up to 3-6 months frozen at -20°C or below. Avoid repeated freeze-thaw cycles. Refer to specific assay manufacturer's stability guidelines.
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 24–72 hours
- Order
- routine
Why Is This Test Done?
Doctors may order a CRP test to monitor conditions like infections (e.g., pneumonia, urinary tract infections), autoimmune diseases (e.g., rheumatoid arthritis), or to assess risk for heart disease. It can also help guide treatment decisions, especially for people with chronic inflammation or recent surgeries.
How Is the Test Performed?
A small blood sample is drawn from a vein, usually in your arm. The blood is sent to a lab where it’s analyzed to measure CRP levels. Results are typically available within 1–3 days.
What Do Results Mean?
CRP levels vary depending on health status. Higher levels may indicate active inflammation, infection, or other medical concerns. Your doctor will interpret results in the context of your symptoms and medical history.
Common Causes of Abnormal Results
Elevated CRP can be caused by infections (bacterial, viral), injuries, surgeries, or conditions like lupus or heart disease. Low levels might suggest no active inflammation, but could also be due to certain medications or chronic conditions.
Reference range
Reference ranges vary significantly depending on the specific cancer-associated antigen (e.g., CEA, AFP, CA 19-9, CA 125, CA 15-3, PSA). Generally, values within the assay-specific normal range are considered negative. Results should be interpreted in conjunction with clinical findings and other diagnostic procedures. Consult the performing laboratory for assay-specific reference intervals.N/A
No special patient preparation is generally required for cancer-associated serum antigen testing. However, certain tumor markers (e.g., PSA) may have specific pre-analytical recommendations. For PSA testing, patients should avoid ejaculation for 24 hours prior to sample collection, and certain urological procedures may affect results. Follow specific assay guidelines if provided.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
CRP is a useful marker for inflammation but isn’t definitive on its own. It’s often used alongside other tests (like blood cultures or imaging) to diagnose or manage health issues. Always discuss results with your healthcare provider.
Short name
CRP (Serum)
Frequently asked questions
What triggers CRP levels to rise?
How often should I get this test?
Can lifestyle changes affect CRP levels?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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