C-reactive protein (CRP) is a substance produced by the liver that circulates in the bloodstream as a biomarker of inflammation. When tissues are injured, infected, or inflamed, the liver increases production, causing the protein’s concentration in the blood to rise rapidly. While measuring CRP is a useful tool for clinicians to gauge the presence and extent of inflammation, the protein itself does not cause physical symptoms. Instead, symptoms are caused by the underlying condition—such as a major infection or an autoimmune flare-up—which simultaneously causes the CRP level to elevate.
The Role of C-Reactive Protein
C-reactive protein is classified as an acute phase reactant, meaning its concentration can increase rapidly within hours of an inflammatory event. This rapid production is primarily triggered by signaling molecules, particularly the cytokine interleukin-6 (IL-6), which is released by immune cells at the site of injury or infection. Once synthesized by the liver, CRP circulates as a protein that plays an important function in the innate immune system.
The protein works by recognizing and binding to specific molecules found on the surface of foreign invaders, like bacteria, and on damaged or dead body cells. By binding to these targets, CRP acts as an early defense mechanism, marking the damaged material for destruction. It facilitates the removal of cellular debris and pathogens by activating the complement system and enhancing phagocytosis, where immune cells engulf and clear the marked substances. CRP levels can be used to monitor the progression of a disease and the effectiveness of its treatment.
Symptoms Associated with Elevated CRP
When CRP elevation is due to an acute condition like a severe infection or major trauma, the associated physical symptoms tend to be sudden and intense. Acute manifestations often include a high fever, chills or sweating, and severe, localized pain at the site of the infection or injury. In cases of systemic infection, such as sepsis, rapid heart rate, persistent vomiting, or even loss of consciousness may occur.
For conditions that cause chronic, low-grade inflammation, the symptoms are more subtle and persistent over a longer duration. Individuals might experience fatigue and a general feeling of being unwell, known as malaise. Other common signs include generalized body aches or joint pain, and a low-grade fever that does not resolve. Unexplained weight loss can also be a sign of systemic inflammatory diseases, such as certain autoimmune disorders or cancers, which cause chronic CRP elevation.
Understanding CRP Test Results
The concentration of CRP in the blood is measured with a blood test, and the results are reported in milligrams per liter (mg/L). A standard CRP test is primarily used to detect significant, acute inflammation, which is common in major infections or inflammatory flare-ups. A normal CRP concentration is considered to be below 10 mg/L. Results between 10 mg/L and 100 mg/L indicate moderate elevation, often seen in conditions like systemic autoimmune diseases or bacterial infections.
Levels exceeding 100 mg/L are considered severely elevated and are commonly associated with acute bacterial infections, which is the most frequent cause. However, a different test, the high-sensitivity CRP (hs-CRP) test, is used to measure much lower levels of the protein for a different purpose. The hs-CRP test is useful for assessing the risk of cardiovascular disease, as low-grade, chronic inflammation plays a role in the development of atherosclerosis. For cardiovascular risk assessment, a result below 2.0 mg/L is considered a lower risk, while results above 2.0 mg/L may suggest an increased risk.
Medical Approach to High CRP Levels
When a blood test confirms an elevated CRP level, the result requires further investigation rather than serving as a single definitive diagnosis. A physician must use the patient’s symptoms, medical history, and other test results to pinpoint the underlying cause. A medical assessment will involve a thorough physical examination and often a series of additional diagnostic tests.
These subsequent tests may include specific antibody panels for autoimmune conditions, cultures to identify bacterial or fungal infections, and imaging studies like X-rays or ultrasounds to locate the source of inflammation. Treatment is directed at resolving the root cause of the inflammation, which lowers the CRP level. This might involve prescribing antibiotics for a bacterial infection, using immunosuppressive medications for an autoimmune disease, or recommending targeted lifestyle changes. It is important to avoid self-diagnosing or attempting self-treatment based only on a high CRP number or general symptoms.