Question

My doctor wanted me to have a CRP level done, and the test came back 4 mg/L. He was a bit worried, so we did it again a week later, and it was 1.2 mg/L.

Is this a useful test, or not? How can it change so much?
 

Answer

C-reactive protein (CRP) blood levels represent the presence of inflammation in the body. Now that it's recognized that inflammation is an underlying cause of atherosclerosis - the degenerative change in arteries that causes heart attacks and stroke - CRP tests have become one way of allocating patients to low- or high-risk categories. There's no doubt that numerous clinical studies have shown an association, or link, between the CRP level and the risk of these serious clinical events. But these links are based on average blood levels obtained from large numbers of patients.
 

A recent study (see publication below) has shown that the CRP level varies in individuals from time to time; the change can be large enough to move them from a "no-risk" to a "average-risk" category, or from "average" to "high-risk". This means one should not pay too much attention to a raised CRP level if that's the only abnormal finding. However, in patients who may be deemed to be at risk based on additional results, the CRP test can help by providing a measure of change in one direction or other. It just shouldn't be used as a screening test (at least, not yet until we know more).

Related Links
MedlinePlus: C-Reactive Protein