C-reactive protein (CRP) is a substance produced by the liver in response to inflammation. Measuring the level of this protein in the blood provides a general marker for inflammation or infection within the body.
Understanding C-Reactive Protein and the Test
C-reactive protein is an acute-phase reactant protein, meaning its levels rapidly increase in response to inflammation and tissue injury. The liver synthesizes CRP, and its concentration in the blood can rise significantly within hours of an inflammatory event or infection. This rapid increase makes it a responsive indicator of the body’s immediate inflammatory state.
The CRP test involves a simple blood draw, typically from a vein in the arm. While CRP effectively signals the presence of inflammation, it is a non-specific marker; it indicates that inflammation exists but does not pinpoint its exact cause or location.
Reasons a CRP Test is Ordered
Doctors frequently order a CRP test to detect inflammation or infection. It helps determine if an inflammatory process is active and its intensity, guiding further diagnostic steps.
The test is also useful in monitoring chronic inflammatory conditions, such as rheumatoid arthritis or lupus, to check for flare-ups or assess the disease’s activity. CRP levels can also help evaluate the effectiveness of treatments for inflammatory conditions. A decrease in CRP levels often indicates that treatment is working and inflammation is subsiding.
Interpreting CRP Test Results
Interpreting CRP test results involves understanding what different levels signify. A CRP level less than 0.9 milligrams per deciliter (mg/dL) or 10.0 milligrams per liter (mg/L) is considered within the normal range, indicating minimal inflammation. However, minor elevations, sometimes between 0.3 to 1.0 mg/dL, can occur due to factors like obesity, pregnancy, or recent minor injury.
Elevated CRP levels suggest the presence of significant inflammation or infection. A moderately elevated level, typically between 1.0 to 10.0 mg/dL, can point to systemic inflammation from autoimmune conditions, a heart attack, or bronchitis. Markedly elevated levels, often above 10.0 mg/dL (or 100 mg/L), usually indicate more acute processes like bacterial infections or major trauma.
A high-sensitivity CRP (hs-CRP) test is a specialized version that can detect much lower levels of CRP, often between 0.3 to 10 mg/L. This test is primarily used to assess an individual’s risk for cardiovascular disease. For hs-CRP, levels below 1.0 mg/L indicate a low risk, while levels between 1.0 and 3.0 mg/L suggest an average risk, and levels above 3.0 mg/L denote a high risk for cardiovascular events.
What Elevated CRP Levels Can Indicate
Elevated CRP levels can point to various underlying conditions, including infections, chronic diseases, and tissue damage. Infections, particularly bacterial ones, commonly lead to significantly increased CRP levels, sometimes exceeding 50 mg/dL. Viral infections can also cause elevations, though usually not as high as bacterial infections.
Inflammatory diseases are another frequent cause of elevated CRP. This includes autoimmune conditions such as rheumatoid arthritis, lupus, and inflammatory bowel disease. Acute pancreatitis, a sudden inflammation of the pancreas, can also result in higher CRP concentrations.
Tissue injury or trauma, like that from surgery or burns, prompts a rapid rise in CRP as the body responds to damage. A heart attack, which involves damage to heart tissue, also leads to elevated CRP levels. For individuals undergoing hs-CRP testing, persistently elevated levels, even at the lower end of the elevated range, can signal chronic, low-grade inflammation associated with an increased risk of cardiovascular disease. This low-grade inflammation contributes to conditions like atherosclerosis. Certain cancers can also cause CRP levels to rise.
CRP is a non-specific marker. Therefore, an elevated CRP result requires further investigation by a healthcare professional. This typically involves additional tests, a thorough physical examination, and a review of the patient’s medical history to determine the exact cause and formulate an appropriate treatment plan.