C-reactive protein is an acute-phase protein made by your liver in response to inflammation in the body.
When tissues are injured or infections occur, the immune system ramps up its defenses by releasing cytokines, especially interleukin 6, which signal your liver to produce more CRP. As a result, CRP levels in your blood rise quickly, making it a useful biomarker for detecting and monitoring inflammation.
Because CRP is a non-specific marker, it doesn’t pinpoint a specific disease on its own. Instead, its elevated presence can indicate a range of conditions, from bacterial infections and autoimmune diseases (like rheumatoid arthritis or lupus) to the inflammation seen after surgery or even low-grade chronic inflammation linked to cardiovascular risk. Physicians often use CRP tests not only to diagnose acute inflammatory episodes but also to monitor the effectiveness of treatments aimed at reducing inflammation.
Interestingly, CRP also plays a direct role in your body's immune response. It binds to certain molecules on dead or dying cells and some types of bacteria. This binding activates the complement system (a series of proteins that assist in eliminating pathogens and damaged cells), marking these cells for clearance by the immune system. This function categorizes CRP as one of the body’s pattern recognition receptors, linking it directly to innate immunity.
Beyond its diagnostic utility, CRP levels can vary: a low level generally suggests little or no inflammation, whereas significantly higher concentrations are markers of active inflammation. In clinical practice, there are standard CRP tests as well as high-sensitivity CRP (hs-CRP) tests, the latter often used to assess cardiovascular risk, as even slight elevations can be associated with underlying low-grade inflammation in blood vessels.