CRP is an acute phase reactant, which can be used as a test for inflammatory diseases, infections, and neoplastic diseases. Progressive increases correlate with increases of inflammation/injury. CRP is a more sensitive, rapidly responding indicator than ESR. CRP may be used to detect early postoperative wound infection and to follow therapeutic response to anti-inflammatory agents. Recent reports have indicated that a highly sensitive version of the CRP assay may be used as an additional indicator for susceptibility to cardiac disease.

CRP arises as a nonspecific response to tissue injury and inflammation.

CRP is a pentameric globulin with mobility near the γ zone. It is an acute phase reactant which rises rapidly, but nonspecifically in response to tissue injury and inflammation. It is particularly useful in detecting occult infections, acute appendicitis, particularly in leukemia and in postoperative patients. In uncomplicated postoperative recovery, CRP peaks on the third postop day, and returns to preop levels by day seven. It may also be helpful in evaluating extension or reinfarction after myocardial infarction, and in following response to therapy in rheumatic disorders. It may help to differentiate Crohn's disease (high CRP) from ulcerative colitis (low CRP), and rheumatoid arthritis (high CRP) from uncomplicated lupus (low CRP).