High CRP: what it means and what happens next

What does a CRP test measure?

CRP stands for C-reactive protein, a protein that the liver makes. Its level in the blood rises when there is inflammation somewhere in the body. Infection and several other causes of inflammation can push the level up.

Doctors usually request the test when they suspect an infection or inflammation, for example after surgery. It is also used to help assess long-term inflammatory conditions such as rheumatoid arthritis and lupus. Lab Tests Online UK says no special preparation is needed for the test.

What does a high CRP mean?

A high or rising CRP suggests that there is an acute infection or inflammation. It does not show where the inflammation is or which condition is causing it. For that reason the test is not diagnostic on its own. Berkshire and Surrey pathology services say a raised CRP is linked with infection, particularly but not only bacterial, and with inflammation.

A small rise is hard to interpret by itself, so doctors consider it alongside the whole clinical picture. In long-term inflammatory conditions the test is often repeated to see whether treatment is working. The cause of a high CRP cannot always be found.

Which conditions can raise CRP?

MedlinePlus lists cancer, heart attack, infection, inflammatory bowel disease, rheumatoid arthritis, lupus and related diseases, and rheumatic fever among the conditions that can raise CRP. Not every cause is an illness. A Danish blood donor study found low-grade inflammation was more common in women using the combined contraceptive pill. Obesity is linked with low-grade inflammation and with higher CRP levels. StatPearls describes smoking, diabetes and other long-term conditions as associated with low-grade inflammation that can raise CRP.

What happens after a high CRP result?

Lab Tests Online UK says CRP is used to assess how severe inflammation is and how well treatment is working. The doctor may then arrange further tests or treatment.

The test is often repeated to see whether treatment has been effective. NHS laboratories often report CRP results within about a day, though timing depends on where the test is requested. A CRP result does not show urgency; the NHS says chest tightness or pain spreading to the arms, neck or jaw needs a 999 call straight away. StatPearls notes that small CRP rises can occur without obvious widespread inflammation.

Is hs-CRP the same test?

High-sensitivity CRP, or hs-CRP, is a separate and more sensitive version of the test. It has been used to estimate the risk of heart disease in people who seem healthy. Lab Tests Online UK notes that current UK guidelines on cardiovascular risk assessment do not recommend hs-CRP testing. A Sheffield NHS laboratory leaflet says hs-CRP should not replace assessment of the usual cardiovascular risk factors. The same leaflet says people with active infection, inflammation or trauma should not have hs-CRP testing until these have resolved.

Can medicines or other factors change the result?

StatPearls states that some medicines, including non-steroidal anti-inflammatory drugs and statins, can lower CRP. Long-term conditions linked with low-grade inflammation can lift it.

Where else is CRP used?

Regional NHS guidance on suspected giant cell arteritis, an inflammation of blood vessels, asks for a CRP before steroids are started. A Devon formulary page says polymyalgia rheumatica is possible but very rare when inflammatory markers are normal. Scottish referral guidance for suspected rheumatoid arthritis refers to CRP and ESR results alongside anti-CCP and rheumatoid factor tests. It advises referral for persistent symptoms even when CRP is normal and antibodies are negative. A Scottish NHS guideline on giant cell arteritis says it is rare to see the condition with normal inflammatory markers, and that CRP, plasma viscosity or both should be raised.