C-reactive protein, serum/plasma concentration
This test measures the level of C-reactive protein, a protein produced by the liver in response to inflammation or infection in your body.
["CRP helps doctors assess inflammation and guide treatment for conditions like infections, autoimmune diseases, or after surgery."]
Key facts at a glance
- LOINC
- 6833-8
- Short code
- CATDANDER
- Synonyms
- Cat Dander IgE Qn
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or red-top clot activator tube
- Units
- N/A
- Ref low
- 0
- Ref high
- 0.34
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 0 years
- Method
- Immunoassay (Fluorescent Enzyme Immunoassay or Chemiluminescent Immunoassay)
- CPT
- 86003
- SNOMED
- 395142008
- Specimen volume
- 1 mL serum (minimum 0.5 mL)
- Stability
- Room temperature: 7 days; Refrigerated (2-8°C): 14 days; Frozen (-20°C or below): 30 days. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 24–72 hours
- Order
- routine
What Is C-Reactive Protein Used For?
CRP is primarily used to detect inflammation in the body. It can help identify infections (such as pneumonia or urinary tract infections), monitor chronic inflammatory conditions (like rheumatoid arthritis), or evaluate the risk of heart disease. Some doctors also use it to check for complications after surgery or trauma.
How Is This Test Performed?
A small blood sample is drawn from a vein, usually in your arm. The blood is then sent to a lab where it is analyzed using an automated immunoassay method to measure CRP levels.
What Does a High or Low CRP Level Mean?
High CRP levels often signal inflammation, infection, or an immune response. Very high levels may indicate severe infections or conditions like sepsis. Low levels may suggest reduced inflammation, but they don’t always mean you’re healthy—other factors can affect CRP.
Common Conditions Monitored with CRP
Doctors may order CRP tests for conditions like heart disease (to assess risk), autoimmune diseases (e.g., lupus, rheumatoid arthritis), infections (e.g., COVID-19, bacterial infections), or to monitor responses to treatments.
Reference range
Negative: <0.35 kU/L; Equivocal: 0.35-0.69 kU/L; Positive (Class 1): 0.70-3.49 kU/L; Positive (Class 2): 3.50-17.49 kU/L; Positive (Class 3): 17.50-49.99 kU/L; Positive (Class 4): 50.00-99.99 kU/L; Positive (Class 5): 100.00-199.99 kU/L; Positive (Class 6): ≥200.00 kU/LN/A
No fasting required. Patient should avoid antihistamine use only if directed by clinician for skin testing correlation; IgE serology is not affected by antihistamines.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
CRP
Frequently asked questions
Why might my doctor order a CRP test?
What are the typical reference ranges for CRP?
Can CRP levels change with diet or exercise?
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