Guidelines published in 2010 from the American Heart Association (AHA) and the American College of Cardiology (ACC) provide guidance to doctors and patients as to when and in whom to measure blood levels of C-reactive protein (CRP).
An elevated blood level of CRP, a marker of inflammation, has been shown in recent years to correlate with an increased risk of cardiovascular events such as heart attacks and strokes. However, interpreting the significance of CRP levels is not always straightforward. Indeed, there remains some confusion within the medical profession as to when it may be appropriate to measure CRP levels, and what to do about them when they are found to be elevated.
This confusion stems from two major points: 1) It is not known whether the CRP itself is playing a role in causing heart disease, or instead if it is merely a marker for increased risk. 2) It is not at all clear that reducing CRP levels itself reduces the risk of cardiovascular events.
What Are the Current Recommendations?
Current recommendations from the AHA and ACC attempt to alleviate some of this confusion.
The AHA/ACC guidelines now state that it is reasonable to measure CRP levels in men over 50 and women over 60 who - on the basis of multiple risk factor scoring with cholesterol levels, weight, level of exercise, smoking history, and presence of hypertension and diabetes - appear to have a low or only a moderately elevated risk of cardiovascular events. In these people, an elevated CRP measurement would indicate that the cardiac risk may very well be substantially greater than it might otherwise appear, and that treatment with statin drugs might then be considered.
For patients who are already known to have high risk, the current recommendations say that measuring CRP levels will not add any substantially new information - if the risk is already known to be high, patients should already be receiving all the therapy available to reduce that risk - including statins. So there is little to be gained by measuring a CRP level.
What CRP Levels Are Considered "Normal"?
The AHA/CDC recommendations specify that "high-specificity CRP" (hs-CRP) levels should be measured. Since levels can fluctuate, they recommend that two separate CRP levels be measured, and then the two values averaged together. Levels less than 1 mg/L are considered "low," levels from 1 to 3 mg/L are considered "average," and levels greater than 3 mg/L are considered "high." High levels may indicate an increased risk of cardiovascular events.
Greenland P, Alpert JS, Beller GA, et al. 2010 ACCF/AHA Guideline for Assessment of Cardiovascular Risk in Asymptomatic Adults: Executive Summary. J Am Coll Cardiol. 2010;56(25):2182-2199. doi:10.1016/j.jacc.2010.09.002