C-reactive protein (CRP) is a substance produced by the liver in response to inflammation in the body. It functions as an acute-phase reactant, meaning its levels in the bloodstream increase rapidly during inflammatory or infectious processes. This protein plays a role in the body’s immune response, helping to identify and eliminate harmful agents.
The Role of CRP Testing
A C-reactive protein test measures CRP in your blood, indicating inflammation from various causes, including bacterial or viral infections.
Healthcare providers also use CRP levels to monitor chronic inflammatory conditions, such as rheumatoid arthritis, lupus, and inflammatory bowel disease. Tracking CRP levels can help assess the severity of these conditions or evaluate the effectiveness of ongoing treatments.
A CRP test indicates inflammation but does not pinpoint its specific cause or location. Additional diagnostic tests are necessary to determine the underlying reason for elevated CRP.
Collecting Blood for CRP
For a C-reactive protein test, blood is typically collected into specific types of tubes to ensure accurate analysis. The most common are those designed to yield serum, the liquid portion of blood after clotting. A serum separator tube (SST), often identified by a gold or tiger-top cap, is frequently utilized. These tubes contain a gel barrier that separates serum from blood cells after clotting and centrifugation. Additionally, a clot activator is present to speed up the clotting process.
Another suitable option for collecting serum is a plain red-top tube. This tube contains no additives, allowing the blood to clot naturally. After clotting, the serum separates from the blood cells upon centrifugation. While serum is generally preferred, some laboratories may also accept plasma for CRP testing. Plasma can be collected in tubes containing anticoagulants like lithium heparin (green cap) or EDTA (lavender cap). Regardless of the tube type, the blood sample must be processed promptly to separate the serum or plasma from cellular components.
Understanding Your CRP Results
After analysis, CRP test results provide insight into the body’s inflammatory status. Healthy individuals generally have low amounts of CRP in their blood. Normal CRP values can vary between laboratories, but levels below 0.3 mg/dL are typically considered normal for most healthy adults.
Elevated CRP levels suggest inflammation or infection. A moderate elevation might indicate systemic inflammation from conditions such as autoimmune diseases or certain infections. Significantly higher CRP levels are often associated with more acute processes, including severe bacterial infections or major tissue injury. CRP results are part of a larger clinical picture. A healthcare professional will interpret your CRP levels in the context of your symptoms, medical history, and other diagnostic tests to make an accurate diagnosis and determine the appropriate course of action.