C-reactive protein (CRP) concentration, serum/plasma
This test measures the level of C-reactive protein, a protein produced by the liver in response to inflammation in your body.
["CRP helps identify inflammation, often used to monitor conditions like infections, autoimmune diseases, or after surgery."]
Key facts at a glance
- LOINC
- 70665-5
- Short code
- COLDAGG
- Synonyms
- CA Ser Ql 18 deg C inc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top serum tube (no anticoagulant) or serum separator tube (SST); pre-warmed tubes preferred to prevent cold adsorption
- Units
- N/A
- Ref low
- 0
- Ref high
- 1
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- deg-c-incubation
- CPT
- 86156
- SNOMED
- 4917004
- Specimen volume
- 3-5 mL of whole blood yielding at least 1-2 mL of serum
- Stability
- Serum should be separated promptly and stored at 37°C if testing is to be performed the same day; if delayed, serum may be stored at 2-8°C for up to 7 days; for longer storage, freeze at -20°C or colder
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 24–72 hours
- Order
- routine
Why Is This Test Done?
Your doctor may order CRP testing to check for signs of inflammation, monitor chronic conditions like arthritis or heart disease, or evaluate responses to treatments. It can also help diagnose infections or assess risks after procedures.
What Does a High or Low CRP Level Mean?
Elevated CRP levels often indicate inflammation or infection, but they can also be normal in some healthy individuals. Low levels may suggest reduced inflammation, but this isn’t always reliable on its own.
Sample Preparation and Testing Process
A blood sample is drawn, typically collected in a tube without additives (to separate serum or plasma). The sample is sent to a lab where it’s analyzed using a sensitive immunoassay method to measure CRP concentration accurately.
Common Conditions Monitored or Diagnosed With CRP
CRP is commonly used to track inflammation in conditions like rheumatoid arthritis, heart disease, or after surgeries. It may also help guide treatment decisions for infections or autoimmune disorders.
Reference range
Negative or titer <1:64 at 18°C; clinically significant cold agglutinins typically present at titers ≥1:64 or ≥1:256 depending on laboratory protocolN/A
No special patient preparation required. However, it is recommended that specimens be drawn and kept at 37°C during transport to prevent in vitro cold agglutinin adsorption and false-negative results. Avoid exposure of the specimen to cold temperatures.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
CRP
Frequently asked questions
What causes CRP levels to change?
How soon after a trigger (like an infection) might CRP levels change?
Can CRP levels be affected by diet or lifestyle?
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