From the Guidelines
C-reactive protein (CRP) is a substance produced by the liver in response to inflammation in the body, serving as a general marker of infection and inflammation, with levels rising when inflammation is present and decreasing when inflammation subsides.
What is C-Reactive Protein
C-reactive protein (CRP) is a protein that increases in the blood when there is inflammation or infection, as well as following a heart attack, surgery, or trauma [ 1 ].
Clinical Use of CRP
When your doctor orders a CRP test, they're looking to detect and monitor conditions causing inflammation, including infections, autoimmune disorders like rheumatoid arthritis, inflammatory bowel disease, or cardiovascular disease [ 1 ].
Interpreting CRP Results
Normal CRP levels are generally below 10 mg/L, with levels above this suggesting inflammation or infection [ 1 ].
- Low risk: CRP levels below 1.0 mg/L
- Average risk: CRP levels between 1.0 to 3.0 mg/L
- High risk: CRP levels above 3.0 mg/L Very high levels (above 50 mg/L) typically indicate serious infection or inflammation [ 1 ].
Mechanism of Action
CRP rises quickly within hours of tissue damage and can increase thousands of times during an acute inflammatory response, making it a valuable early indicator of infection or inflammation before other symptoms might appear [ 1 ]. This protein works as part of your immune system by binding to damaged cells or certain bacteria to activate complement proteins that help clear pathogens from the body [ 1 ].
From the Research
Definition and Function of C-Reactive Protein
- C-reactive protein (CRP) is a plasma protein that is evolutionarily conserved, found in both vertebrates and many invertebrates 2.
- It is a member of the pentraxin superfamily, characterized by its pentameric structure and calcium-dependent binding to ligands like phosphocholine (PC) 2.
- CRP is secreted by the liver in response to a variety of inflammatory cytokines and its levels increase very rapidly in response to trauma, inflammation, and infection 3.
- The function of CRP is felt to be related to its role in the innate immune system, where it acts as a surveillance molecule for altered self and certain pathogens 3.
Biological Properties and Roles
- CRP exists in conformationally distinct forms, which exhibit distinct functional properties and help explaining the diverse, often contradictory effects attributed to CRP 4.
- The native pentameric CRP (nCRP) can irreversibly dissociate at sites of inflammation and infection into five separate monomers, termed monomeric CRP (mCRP) 5.
- nCRP often exhibits more anti-inflammatory activities compared to mCRP, which promotes the chemotaxis and recruitment of circulating leukocytes to areas of inflammation 5.
- CRP plays important roles in inflammatory processes and host responses to infection, including the complement pathway, apoptosis, phagocytosis, nitric oxide (NO) release, and the production of cytokines 5.
Clinical Significance
- CRP is a sensitive biomarker of inflammation and its levels have been monitored to gauge disease severity or to predict disease progression and outcome 4.
- Elevations in CRP level have been implicated as a useful marker to identify patients at risk for cardiovascular disease and certain cancers 4.
- CRP has a distinct status of a disease marker in cardiovascular diseases and is well known for its clinical and pathological significance 6.