C-reactive protein, or CRP, is a substance frequently measured in healthcare settings. While it does not diagnose a specific condition, its levels indicate the presence of inflammation or infection.
Why it’s Called “C-Reactive”
The “C” in C-reactive protein refers to its ability to react with a specific component found in bacteria. This protein was discovered in 1930 when researchers observed it binding to the “C-polysaccharide” present in the cell wall of Streptococcus pneumoniae. This binding occurs in the presence of calcium and targets phosphocholine-containing substances. The protein was named “C-reactive” due to this distinctive reactivity.
What C-Reactive Protein Does
C-reactive protein serves as an acute-phase reactant, meaning its concentration in the blood increases in response to inflammation or infection. The liver is the primary site of CRP production, releasing it into the bloodstream within hours of tissue injury or the onset of inflammation. As a component of the innate immune system, CRP plays a role in the body’s early defense mechanisms. It functions by recognizing and binding to damaged cells, nuclear antigens, and various pathogenic microorganisms.
Upon binding, CRP initiates several immune responses. It can activate the complement system, a cascade of proteins that helps clear pathogens and damaged cells from the body. CRP also acts as an opsonin, marking pathogens for destruction by immune cells like phagocytes. These actions contribute to the removal of harmful substances and cellular debris.
Interpreting CRP Levels
Elevated levels of C-reactive protein indicate the presence of inflammation or infection within the body. However, CRP is considered a non-specific marker, meaning it signals that something is amiss without pinpointing the exact cause or location of the issue. For instance, a high CRP level could be due to a bacterial infection, a chronic inflammatory condition like arthritis, or even tissue damage from a heart attack. Greater CRP concentrations suggest more severe inflammation or infection.
Healthcare providers consider CRP results as one piece of a larger diagnostic puzzle. They combine CRP levels with a patient’s symptoms, medical history, and other diagnostic tests to determine the underlying cause of the inflammation. While a normal CRP level is less than 10 mg/L, values above this range suggest inflammation. Interpretation of these levels should always be done by a medical professional.