C-reactive Protein (CRP) Overview. C-reactive protein (CRP) is a marker of inflammation in the body. Therefore, its level in the blood increases if there is any inflammation in the body.C-reactive protein, along with other markers of inflammation (erythrocyte sedimentation rate, or ESR) are also sometimes referred to as acute phase reactants.C-reactive protein is produced by the cells in the liver.-reactive Protein (CRP) Overview. C-reactive protein (CRP) is a marker of inflammation in the body. Therefore, its level in the blood increases if there is any inflammation in the body.