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CRP is an abbreviation for “C-Reactive Protein”. This protein was first discovered in the blood of patients who had streptococcal infections. It reacted with a portion of the streptococci that is called “C Carbohydrate”, hence it was designated “C-Reactive Protein.” Even though it was first found in Strep infections, we now know that it can be seen in virtually all infectious diseases, and in many inflammatory processes. It is one of a group of proteins called “acute phase reactants” that can be found in the blood during inflammatory or infectious processes.
For inflammatory processes, Normal CRP is usually considered to be less than 1.0 mg/dl. Moderate inflammation is characterized by levels between 1.0 and 10.0 mg/dl, and values above 10.0 mg/dl are considered a sign of marked inflammation.
When inflammation occurs, the body has a number of non-specific responses to help combat what it perceives to be a potential infection. Several proteins are produced that have activity against microbes, CRP being one of these.
Elevation of the CRP usually indicates that an inflammatory process is happening somewhere in the body. The CRP does not indicate any specific disease process, nor does it indicate the prognosis for the patient. Multiple CRP levels measured during and after the inflammatory process may be helpful in predicting remission from the inflammation. The CRP is elevated in a lot of different conditions.
In the past few years, very sensitive CRP assays have been used to detect levels of CRP that are in the “normal” range (0-1.0 mg/dl). Some of these studies have shown that low levels of CRP are seen in patients who have atherosclerotic plaque in their coronary arteries. At least one of these studies showed a strong correlation between this persistent CRP and heart attacks in women.
They are both tests that measure inflammation, but they are affected by different aspects of the inflammatory process. The CRP appears very rapidly (within a few minutes) when an inflammatory process begins, and tends to drop after several days. The Sed Rate tends to come up more slowly (a few days after onset of the inflammation), and persists for a longer period of time. In chronic inflammation, like we see in autoimmune diseases, both CRP and Sed Rate may stay elevated for long periods of time. Depending on the source of the inflammation, the CRP and Sed Rate may give very different results
