C-reactive protein (CRP) is an acute-phase protein produced by the liver in response to injury or tissue damage. It has been assayed for many years as a non-specific marker of acute inflammatory diseases, infections, neoplastic diseases, and other conditions where inflammation occurs. It is still used in this manner as a marker of inflammation though it is very nonspecific. The concentration measured by CRP assays is typically 5-20 mg/L.
Recall from earlier that atherosclerosis is, at its etiology, a chronic inflammatory condition. Because of this fact, CRP has been used as a marker for cardiovascular risk. However, conventional CRP assays are not sensitive enough to detect the subtle changes seen in cardiovascular disease. Instead, newer, high sensitivity CRP assays were developed to meet this need. They are called high sensitivity CRP assays (hsCRP). The hsCRP assays can detect CRP at lower concentrations (0.5-10.0 mg/L). This allows for measurement of the CRP protein in patients who would be below the limit of detection with the conventional CRP assay. Note that hsCRP assays measure the same protein. Therefore, patients with high CRP (due to acute inflammation) cannot be assessed for cardiovascular risk using hsCRP assays.