CRP and inflammation: what a blood test can and cannot tell you
CRP is the most common blood test for inflammation. Learn what the result means, the difference between standard and high-sensitivity CRP, and its link to heart health.
C-reactive protein, or CRP, is a protein made by the liver. When there is inflammation somewhere in the body, the liver releases more CRP into the blood within hours. That makes CRP one of the most widely used blood tests in healthcare, and also one of the most discussed in cardiovascular research.
Two kinds of CRP test
- Standard CRP is used to detect and follow larger inflammatory reactions, such as bacterial infections or flares of inflammatory diseases. It helps doctors decide, for example, whether an infection is likely to need antibiotics, and whether a treatment is working.
- High-sensitivity CRP (hs-CRP) measures much lower levels. It is used to detect the mild, long-lasting inflammation that is linked to heart disease.
What the numbers can mean
CRP is measured in milligrams per litre (mg/L). In healthy people, levels are usually low. During a serious bacterial infection they can rise to well over 100. For heart risk, hs-CRP results are often grouped as follows:
- below 1 mg/L: lower risk
- 1 to 3 mg/L: average risk
- above 3 mg/L: higher risk
A single raised value does not say much, because a cold, a small injury or a hard workout can raise CRP for a few days. If hs-CRP is used to assess heart risk, it is usually measured twice, a couple of weeks apart, when you are well.
What CRP cannot tell you
CRP shows that there is inflammation, not where it is or what is causing it. A raised CRP can be due to an infection, an autoimmune disease such as rheumatoid arthritis, an injury, overweight or smoking. A normal CRP does not rule out disease either. That is why the test is always interpreted together with symptoms, an examination and other tests.
CRP and the heart
Large studies have shown that people with slightly raised hs-CRP have a higher risk of heart attack and stroke, even when their cholesterol is normal. This was an important piece of evidence that inflammation plays a role in atherosclerosis. Later trials showed that dampening inflammation can lower the risk of new events in people who already have heart disease, which we describe in the research background.
For most people, hs-CRP is not a routine test. Doctors may use it to fine-tune the risk assessment when it is unclear whether someone should start preventive treatment.
Can you lower your CRP?
The things that lower low-grade inflammation are the same things that protect the heart: not smoking, regular physical activity, losing weight if you are overweight, a diet rich in vegetables, fruit, whole grains and fish, and good sleep. Our guide to anti-inflammatory foods has practical tips. Some medicines, including statins, also lower CRP.
If you have received a CRP result and are unsure what it means, ask the doctor who ordered the test to explain it in relation to your situation.
This article is general information and not medical advice. If you have symptoms or questions about your own health, talk to a doctor. In an emergency, call your local emergency number.
