C-reactive protein (CRP) is a glycoprotein produced during acute inflammation or tissue destruction. The protein gets its name from its ability to react (or cross-react) with Pneumococcus somatic C-polysaccharide and precipitate it. The CRP level is not influenced by anemia or plasma protein changes. It begins to rise about 4-6 hours after onset of inflammation and has a half-life of 5-7 hours, less than one-fourth that of most other proteins that react to acute inflammation. For many years the standard technique was a slide or tube precipitation method, with the degree of reaction estimated visually and reported semiquantitatively. The test never enjoyed the same popularity as the ESR because the result was not quantitative and the end point was difficult to standardize due to subjective visual estimations. Recently, new methods such as rate reaction nephelometry and fluorescent immunoassay have enabled true quantitative CRP measurement. CRP determination using the new quantitative methods offers several important advantages over the ESR, including lack of interference by anemia or serum protein changes, fewer technical problems, and greater sensitivity to acute inflammation because of shorter half-life of the protein being measured. Many now consider quantitative CRP measurements the procedure of choice to detect and monitor acute inflammation and acute tissue destruction. ESR determination is preferred, however, in chronic inflammation. There is some evidence that CRP levels are useful in evaluation of postoperative recovery. Normally, CRP reaches a peak value 48-72 hours after surgery and then begins to fall, entering the reference range 5-7 days after operation. Failure to decrease significantly after 3 days postoperatively or a decrease followed by an increase suggests postoperative infection or tissue necrosis. For maximal information and easier interpretation of the data, a preoperative CRP level should be obtained with serial postoperative CRP determinations.

General clinical indications for CRP are essentially the same as those listed for the ESR. A growing number of investigators feel that the true quantitative CRP is superior in many ways to the ESR.