Elevated CRP is associated with an increased risk for cardiovascular events, such as heart attack and stroke. Whether CRP actually causes the increased risk or is just a marker for it is still not known - but now we do know that treating people who have high CRP levels with statins can reduce their risk. This fact alone makes measuring CRP worthwhile in many individuals.
CRP is a protein that is released into the bloodstream during periods of inflammation. Since atherosclerosis (the process that forms plaques in the arteries) is now thought to be at least partly an inflammatory process, it makes sense that CRP levels might be elevated during periods of active plaque formation, and that high levels of CRP would correlate with cardiovascular events.
CRP is measured using a high sensitivity test (called the hs-CRP blood test). In general, the higher the hs-CRP level, the higher the risk. Levels of hs-CRP below 1 are considered low; levels of 1 - 3 are considered moderately elevated; levels greater than 3 are considered high. Levels greater than 10 are usually only seen with active, obvious inflammatory processes, such as severe infection, major trauma, or chronic inflammatory diseases - these ultra-high levels cannot be used to interpret cardiac risk. Because CRP levels can fluctuate over time, most experts now recommend measuring 2 CRP levels a few weeks apart, and averaging the two values.
Deciding whether measuring CRP should be part of the routine screening process has been difficult for two reasons. First, interpreting the significance of an elevated CRP level is often not straightforward, and can lead to more confusion rather than less. Second, until recently it was unclear whether treatment should be changed based on the results of CRP values.
In most patients, elevated levels of CRP are associated with the presence of several other risk factors for cardiovascular disease, such as smoking, obesity, sedentary lifestyle, increased cholesterol, hypertension and metabolic syndrome. The highest levels of CRP are usually seen in patients with the greatest number of additional risk factors. So often, finding a high CRP level merely confirms what already is quite apparent - the patient has a high risk of cardiac disease, and needs aggressive risk factor modification (most likely including statins) whatever their CRP levels.
On the other hand, an elevated CRP level in patients whose other risk factors place them in a moderate or even a low risk category does add new and important information. For these patients, a high CRP level probably indicates that their risk is higher than it otherwise appears. It means that that little bit of hypertension, or that little bit of extra weight, is indeed producing inflammation within your blood vessels, and is increasing your risk.
So, at the very least, elevated CRP levels should make you and your doctor much more serious about risk reduction. Furthermore, data from the recent JUPITER study tells us that giving statins to apparently healthy patients who have high CRP levels can substantially and signficantly reduce their risk of cardiovascular disease.
The bottom line
While CRP levels do not need to be measured in everybody. The first thing that ought to be done is for your doctor (or you yourself) to assess your baseline risk of cardiac disease, based on the more obvious risk factors. ( You can do your own cardiac risk assessment here.) This assessment will tell you whether you are in a high, intermediate, or low risk category.
If you are already in a high risk category, measuring CRP may not be that helpful. You're probably going to have a heart attack or stroke unless you aggressively reduce your risk, no matter what the CRP level. But if you or your doctor are hesitant to use statins, and are unsure of the benefit they may provide you, then measuring your CRP levels may give you one more reason to consider these risk-reducing drugs.
It makes good sense to measure a CRP level if you are in the moderate risk category. An elevated CRP level here should send up the red flags that your risk is probably higher than you think. Also, if your cholesterol levels are normal or only a little elevated, then knowing that your CRP is high would give you and your doctor a clear-cut reason to consider therapy with statins.
With today's state of knowledge, the value of measuring CRP levels in people in the low risk is less clear. If the CRP is elevated and you have no other risk factors, the use of statins could be considered but is controversial. However, if all your other risk factors are in good shape but you have a strong family history of cardiovascular disease - especially if you are a woman - using statins to reduce your CRP level would be far less controversial.
If you do have your CRP measured and it comes back high, you may want to read this article: What To Do When Your CRP Is Elevated.
Sources:
1. Cook NR, Buring JE, and Ridker PM. The effect of including C-reactive protein in cardiovascular risk prediction models for women. Ann Intern Med 2006; 145:21-29.
2. Lloyd-Jones DM, Liu K, Tian L, and Greenland P. Narrative review: Assessment of C-reactive protein in risk prediction for cardiovascular disease. Ann Intern Med 2006; 145:35-42.
3. Davey Smith G, Timpson N and Lawlor D. C-reactive protein and cardiovascular disease risk: Still an unknown quantity? Ann Intern Med 2006; 145:70-72.
Ridker PM, Danielson E, Fonseca FA et al. Rosuvastatin to prevent vascular events in men and women with elevated C-reactive protein. New Engl J Med 2008; DOI: 10.1056/NEJMoa0807646. Available at: http://www.nejm.org.
