In medicine, an acute-phase reactant (APR) is a protein that the body produces in response to inflammation, injury, or infection. The liver is the main source of APRs, and they are synthesized and released into the bloodstream within a few hours of an inflammatory stimulus.
Some common acute-phase reactants include C-reactive protein (CRP), fibrinogen, haptoglobin, serum amyloid A (SAA), and ferritin. These proteins play various roles in the immune response to inflammation and infection, such as activating complement pathways, enhancing phagocytosis, and binding and sequestering iron to limit bacterial growth.
Measuring levels of acute-phase reactants can be useful in diagnosing and monitoring inflammatory and infectious conditions, as well as assessing disease severity and response to treatment. For example, CRP is often used as a marker of systemic inflammation and infection, and elevated levels can indicate conditions such as bacterial pneumonia, rheumatoid arthritis, and inflammatory bowel disease.
