CRP Blood Test: What a High C-Reactive Protein Result Means

CRP is one of the most common blood tests in hospitals and clinics. It tells you whether there is inflammation somewhere in the body, but not where or why.

Imagine getting a text from your clinic saying your CRP is “raised” with no other explanation. You search online and find everything from a cold to cancer. Here is what it really means.

What CRP is

C-reactive protein (CRP) is made by the liver. Levels rise quickly, within hours, when there is inflammation or infection, and fall as it settles. That makes it useful for tracking illness and response to treatment.

Typical results

• Normal: many labs use below 5 mg/L, some below 10 mg/L
• Mildly raised (about 10 to 40 mg/L): often viral infections, minor injuries or inflammatory conditions
• Higher (often above 100 mg/L): more often linked to bacterial infection or significant inflammation, but not always

What can raise CRP

• Infections, especially bacterial
• Inflammatory conditions such as rheumatoid arthritis or inflammatory bowel disease
• Surgery, injury or burns
• Some cancers
• Obesity, smoking and pregnancy can raise it slightly

High-sensitivity CRP (hs-CRP)

hs-CRP measures very low levels and is sometimes used to help estimate heart disease risk. Under 1 mg/L is often described as low risk, 1 to 3 mg/L as average and above 3 mg/L as higher risk.

What a CRP result cannot tell you

CRP is non-specific. It does not show what is causing inflammation. Healthcare providers interpret it alongside symptoms, examination and other tests such as a full blood count.

Lab ranges vary

Reference ranges differ between laboratories and countries, and some use different units. Always compare your result with the range printed on your report and discuss it with your healthcare provider.

Frequently asked questions

Is CRP the same as ESR?

No. Both measure inflammation, but CRP changes faster. ESR rises and falls more slowly.

Can stress raise CRP?

Long-term stress and poor sleep may cause small rises, but they do not cause very high CRP.

Should I repeat the test?

Your clinician may repeat CRP to see if it is falling with treatment.

But my CRP is only slightly high. Should I worry?

Usually not on its own, especially if you feel well. Seek urgent help if you have a high fever, are very unwell or have signs of sepsis.

Related: Full blood count explained · Normal lab values cheat sheet

Sources: Lab Tests Online UK, NHS, MedlinePlus (US National Library of Medicine), American Heart Association.