Blood test
C-Reactive Protein Test (CRP)
A CRP test measures C-reactive protein, a substance the liver makes when there is inflammation in the body. It helps detect and monitor infection and inflammatory conditions.
Quick answer
C-Reactive Protein Test (CRP): what it is and what the results mean
C-reactive protein (CRP) is a protein released into the blood when there is inflammation. A CRP blood test measures its level as a general marker of how much inflammation is present.
- Why it is done: It is used to help detect infection and inflammation, to gauge how severe they are, and to monitor the response to treatment in conditions such as infections and inflammatory diseases.
- Understanding results: A raised CRP suggests inflammation somewhere in the body but does not say where or why — it may reflect infection, injury or an inflammatory condition.
What it is
C-reactive protein (CRP) is a protein released into the blood when there is inflammation. A CRP blood test measures its level as a general marker of how much inflammation is present.
Why it is done
It is used to help detect infection and inflammation, to gauge how severe they are, and to monitor the response to treatment in conditions such as infections and inflammatory diseases.
What to expect
A standard blood sample is taken from the arm; no fasting is needed and results are often available quickly.
Understanding the results
A raised CRP suggests inflammation somewhere in the body but does not say where or why — it may reflect infection, injury or an inflammatory condition. A very high level often points to significant infection or inflammation, and falling levels usually indicate improvement.
Good to know
Risks and limitations
The test carries the minor risks of any blood test. Because CRP is non-specific, an abnormal result usually prompts further assessment to find the cause rather than giving a diagnosis by itself.
Education and reference only. This explains the test in general terms and is not medical advice. Always follow the specific instructions from the team arranging your test, and discuss your results with your clinician.
Answers
C-Reactive Protein Test (CRP): frequently asked questions
What does a high CRP mean?
A raised CRP shows there is inflammation in the body, which can be due to infection, injury or an inflammatory condition. It does not identify the exact cause, so it is interpreted with your symptoms and other tests.
What is the difference between CRP and ESR?
Both detect inflammation. CRP rises and falls quickly, making it useful for tracking rapid changes, while the ESR changes more slowly and can reflect longer-term inflammation. They are sometimes done together.
Related tests
Other blood test investigations
Sources
Where this is drawn from
- NHS — Tests and treatments
- NICE — diagnostic guidance
- Royal College of Pathologists / relevant professional body
Building patient-education content for tests or procedures?
We create clear, accurate, referenced medical explainers and decision aids for teams.