C-reactive protein, usually shortened to CRP, is one of the most widely used blood markers in medicine. It is a protein made by the liver, and its level in the blood rises whenever there is inflammation somewhere in the body. Because it responds quickly and reliably, it has become a go-to test for spotting and tracking inflammation — but on its own it rarely tells the whole story.
What CRP actually measures
CRP is part of your body's natural response to injury, infection and inflammation. When tissue is damaged or your immune system is activated, chemical signals prompt the liver to release more CRP into the bloodstream. Levels can climb within hours and fall again just as fast once the trigger settles, which makes CRP a useful snapshot of what is happening right now rather than weeks ago.
There are two ways it is commonly reported. Standard CRP is used to detect and monitor obvious inflammation, such as an infection. High-sensitivity CRP (hs-CRP) measures much lower levels precisely and is used differently — mainly to help assess long-term cardiovascular risk, where low-grade, persistent inflammation may play a role.
What a raised CRP can point to
A high CRP simply tells you inflammation is present; it does not say where or why. Common reasons include:
- Infections — bacterial infections in particular can push CRP up sharply.
- Injury or recent surgery — tissue healing raises CRP temporarily.
- Autoimmune and inflammatory conditions — such as rheumatoid arthritis or inflammatory bowel disease.
- Chronic low-grade inflammation — linked to factors like excess weight, smoking and cardiovascular risk.
Because so many things can raise it, doctors interpret CRP alongside your symptoms and other tests rather than treating the number in isolation.
What a low or normal CRP means
A low CRP is generally reassuring — it suggests there is little active inflammation at the moment. It does not rule everything out, though. Some conditions cause inflammation that comes and goes, and a single normal result taken on a good day may miss it. This is why doctors sometimes repeat CRP over time or pair it with a second inflammation marker such as ESR.
Check your CRP
A simple blood test measures hs-CRP to check for inflammation, giving you and your doctor a clear reading to interpret alongside your symptoms.
Check your CRPHow CRP is used to track health over time
One of CRP's biggest strengths is monitoring. Because it rises and falls quickly, it is useful for watching how an infection or inflammatory condition responds to treatment — a falling CRP is often an encouraging sign. For cardiovascular risk, hs-CRP is considered as one piece of a broader assessment that also includes cholesterol, blood pressure and lifestyle factors.
When to get checked
Testing CRP can be sensible if you have unexplained symptoms such as persistent fever, joint pain, or general feeling of being unwell, or if you are building a fuller picture of your cardiovascular health. It is not a screening test to do in isolation without reason. If your result is raised and you feel unwell, or you have ongoing symptoms, speak to a clinician who can put the number in context and decide whether further tests are needed.
Check your CRP
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Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic