C-reactive protein (CRP) is an annular (ring-shaped), pentameric protein found in blood plasma. CRP is synthesized by the liver in response to factors released by macrophages and fat cells (adipocytes). It is an acute-phase protein of hepatic origin that increases following interleukin-6 secretion by macrophages and T cells. Its physiological role is to bind to lysophosphatidylcholine expressed on the surface of dead or dying cells (and some types of bacteria) in order to activate the complement system via the C1Q complex. It is not related to C-peptide (insulin) or protein C (blood coagulation).
CRP is used mainly as a marker of inflammation, whose levels rise in response to inflammation. Recent research suggests that patients with elevated basal levels of CRP are at an increased risk of diabetes, hypertension and cardiovascular disease.