C-Reactive Protein (CRP)

C-reactive protein, or CRP, is an acute-phase protein whose concentration in the blood can rise substantially during inflammation. It is produced mainly by the liver in response to inflammatory signaling, particularly cytokines such as interleukin-6. CRP participates in innate immune processes, including recognition of damaged or altered material and activation of parts of the complement system .^1,2

A blood CRP measurement is therefore used as a nonspecific marker of inflammatory activity. A high value can occur with many different triggers, including infection, tissue injury, and inflammatory disease, so CRP does not by itself identify the cause or location of inflammation. Its concentration can also change quickly as the underlying inflammatory stimulus changes, which makes serial measurements useful in some clinical settings .¹

Standard CRP testing and high-sensitivity CRP, or hs-CRP, measure the same protein but are optimized for different concentration ranges. High-sensitivity assays can quantify lower CRP levels more precisely and are used in some cardiovascular risk assessments. CRP should also be distinguished from inflammatory cytokines: cytokines are signaling molecules that help coordinate inflammation, whereas CRP is a downstream acute-phase protein produced in response to that signaling .^1,2