hs-CRP is most often used to help predict a healthy person's risk of cardiovascular disease.

People who have hs-CRP results in the high end of the normal range have 1.5 to 4 times the risk of having a heart attack as those with CRP values at the low end of the normal range.

The CRP molecule itself is not a harmful molecule in the body. The higher level of CRP is simply a reflection of higher than normal inflammation. The measurement of CRP does not reflect where the inflammation is. It may come from cells in the fatty deposits in arterial walls that reflect the process of atherosclerosis. It may come from other tissues.

Unfortunately, there is no agreement about exactly when the test should be ordered and on whom the test should be done. There is not yet a consensus about its value, but the test is being promoted by some as a test to help determine risk for cardiovascular disease, heart attacks, and strokes.

hs-CRP usually is ordered as one of several tests in a cardiovascular risk profile, often along with tests for cholesterol and triglycerides. Some experts say that the best way to predict risk is to combine a good marker for inflammation, like CRP, along with the ratio of total cholesterol to HDL cholesterol.

To help clarify when CRP testing may be most useful, in January 2003 the American Heart Association and Centers for Disease Control and Prevention (AHA/CDC) examined current evidence and then published their recommendations for its use:

No: not for widespread screening of the general adult population; continue to focus on major risk factors, such as high blood pressure, high cholesterol, smoking and diabetes

Yes: useful as an independent marker of risk and as a “discretionary tool” in the evaluation of those with moderate risk of cardiovascular disease to help determine treatment course

No: not for tracking treatment efficacy due to lack of evidence that reducing hs-CRP levels improves outcomes, such as survival

The results are generally interpreted on a relative scale. People with the highest values have the highest risk of cardiovascular disease and those with the lowest values have the lowest risk. This is often expressed in terms of percentiles. These may be quintiles (five divisions), quartiles (four divisions), or tertiles (three divisions). For example, one large study showed that those people in the top quintile of CRP (the 20% of people with the highest CRP values) have about twice the risk of heart disease as those people in the bottom quintile (the 20% of people with the lowest CRP values).

The AHA/CDC defined risk groups as follows:

Low risk: less than 1.0 mg/L

Average risk: 1.0 to 3.0 mg/L

High risk: above 3.0 mg/L

Taking nonsteroidal anti-inflammatory drugs (like aspirin, Advil, Motrin, and Naproxin) or statins may reduce CRP levels in blood. Both anti-inflammatory drugs and statins may help to reduce the inflammation, thus reducing CRP.

Because hs-CRP tests are measuring a marker of inflammation, it is important that any person having the test be healthy in order for the test to be of any value in predicting the risk of coronary disease or heart attack. Any recent illness, tissue injury, infection, or general inflammation will raise the amount of CRP and give a falsely elevated estimate of risk.

Since the hs-CRP and CRP tests measure the same molecule, people with chronic inflammation, such as those with arthritis, should not have hs-CRP levels measured. Their CRP levels will be very high due to the arthritis—often too high to be measured using the hs-CRP test.