C-reactive protein (CRP) is a protein produced by the liver in response to inflammation anywhere in the body. It is an acute phase reactant whose levels can rise more than 1000-fold within 24–48 hours of an inflammatory stimulus, making it one of the most sensitive and rapid markers of inflammation available.

CRP is non-specific — it rises with any inflammatory trigger regardless of cause. This makes it valuable for detecting inflammation but it cannot identify which organ or condition is responsible. Standard CRP detects moderate-to-large elevations from acute illness; high-sensitivity CRP (hs-CRP) measures lower levels relevant to cardiovascular risk.