What Is a C-Reactive Protein?
If you have high cholesterol, you've probably been told to lower the LDL number from your blood test. LDL is the "bad cholesterol," the type that contributes to plaque that can clog your arteries. This can lead to a heart attack or stroke.
But that's only part of the story. Research shows that only 50% of people who've had heart attacks had high LDL levels. So, many doctors use another test, called the C-reactive protein test, to help figure out who’s at risk.
C-reactive protein (CRP) is produced by the liver. Its level rises when there's inflammation in your body. LDL cholesterol not only coats the walls of your arteries, but it also damages them. This damage causes inflammation that the body tries to heal by sending a "response team" of proteins called "acute phase reactants." CRP is one of these proteins.
Why Is a C-Reactive Protein Test Done?
The C-reactive protein (CRP) test measures the level of C-reactive protein in your blood.
One study found that testing for CRP levels is a better indicator of cardiovascular disease (CVD) than the LDL test. But, a CRP test is not a test for heart disease. It's a test for inflammation in the body.
The test is also used for people who have autoimmune diseases like lupus and rheumatoid arthritis. These conditions also cause inflammation. A doctor might test someone with either condition to see if anti-inflammatory medication is working, though the CRP test cannot show where the inflammation is taking place in the body.
Other things you can do with this test include:
- Check for infections, like sepsis (bodily inflammation), or fungal or bone infections.
- Learn your risk of heart disease.
- Learn your risk of having a second heart attack.
- Check for inflammatory bowel disease or pelvic inflammatory disease.
- Check for lung disease.
When Would I Need a C-Reactive Protein (CRP) Test?
Your doctor may order a CRP test if you have symptoms of an infection such as:
- Fever
- Chills
- Rapid heart beat
- Rapid breathing
- Nausea and vomiting
Your doctor may also order the test if you have a condition that causes inflammation, like an autoimmune disease.
C-Reactive Protein Test Preparation
It’s a simple blood test. A sample is drawn from a vein, most likely in your arm. No special preparation (like fasting) is needed, and the test is not painful beyond a sting on the arm from where needle goes in. The test may be affected by medications you take, so ask your doctor if you need to cut back beforehand. The blood sample is tested at a lab.
C-Reactive Protein Test Result
Each lab will set its own ranges for normal. The table below gives a general overview of CRP levels and what they might mean.
C-Reactive Protein Level Chart
| CRP LEVEL | CLASSIFICATION | POSSIBLE REASON |
| Less than 0.3 mg/dL (milligrams per deciliter) | Normal | Normal |
| 0.3 to 1.0 mg/dL | Normal or minor elevation | obesity, pregnancy, depression, diabetes, cold, sedentary lifestyle |
| 1.0 to 10.0 mg/dL | Moderate elevation | Bodily inflammation (rheumatoid arthritis or other autoimmune diseases), heart attack, pancreatitis, bronchitis |
| More than 10.0 mg/dL | Marked elevation | Acute bacterial infections, viral infections, systemic vasculitis, major trauma |
| More than 50.0 mg/dL | Severe elevation | Acute bacterial infections |
High CRP Levels: What Do They Mean?
Results that are greater than 10 milligrams per deciliter (mg/dL) are considered to be high. High levels usually mean you have some kind of inflammation in your body. This might be due to an infection, a serious injury, or an ongoing disease, like inflammatory bowel disease or rheumatoid arthritis. But the test won't tell you what is causing the inflammation. For that, the doctor would have to run other tests.
You could also have a high level because you're in the second half of your pregnancy or you're using birth control pills.
Moderate elevation
If your CRP level is between 1 and 10 mg/dL, you could have:
- Bodily inflammation from autoimmune diseases such as rheumatoid arthritis or lupus
- Heart attack
- Pancreatitis
- Bronchitis
Marked elevation
If your CRP level is between 10 and 50 mg/dL, you could have:
- Acute bacterial infections
- Viral infections
- Systemic vasculitis (inflammation of the arteries and veins)
- Major trauma (an injury that is severe or could cause death)
Severe elevation
A CRP level of over 50 mg/dL is linked to bacterial infections 90% of the time. These include hepatitis C, dengue, and malaria.
C-Reactive Protein Test for Heart Disease
A variation of the CRP test, the high-sensitivity CRP (hs-CRP), is used to check for cardiovascular disease (CVD). The hs-CRP test is most useful for people who have a 10%-20% chance of having a heart attack within the next 10 years. The test is not helpful for people with a higher or lower risk.
CRP seems to predict the chance of having heart problems at least as well as cholesterol levels. A study found that elevated levels of C-reactive protein were linked to a three times greater risk of a heart attack.
Here are what the results mean:
- hs-CRP level lower than 1.0 milligrams per liter (mg/L) – low risk of CVD (heart disease)
- hs-CRP level of 1.0 mg/L to 3.0 mg/L – moderate risk of CVD
- hs-CRP level of more than 3.0 mg/L – high risk of CVD
Because your CRP level can vary, the test should be done two times (2 weeks apart) to find your risk of heart disease. You could also have a high reading without necessarily having heart disease. So it's important to check your LDL levels as well to get a full picture of your CVD risk.
What's the Treatment for High C-Reactive Protein?
If your CRP level is intermediate or high, you should make the following changes to reduce your chances of heart disease:
- Eat a heart-healthy diet.
- Get your high cholesterol down.
- Keep your weight where it should be.
- Exercise regularly.
- If you have diabetes or high blood pressure, manage it.
- If you smoke or use tobacco in another way, quit.
- If you drink alcohol, do so responsibly.
Statins, the most commonly prescribed cholesterol-lowering drugs, may reduce your risk of heart disease if your CRP is high. But if your cholesterol level is normal or low, a statin may not be the answer for your high CRP level. Talk to your doctor about which treatments are best for you.
Takeaways
The CRP test measures the level of C-reactive protein in your blood. This protein is produced by your liver, and its level rises when there's inflammation in the body. The test can tell you whether you might have an infection, certain diseases, or are at risk of heart disease. But your doctor usually has to run more specific tests to find the reason for your high CRP level.
C-Reactive Protein FAQs
What level of C-reactive protein indicates infection?
Above 10 mg/dL (milligrams per deciliter). But your doctor would have to run more tests to confirm that an infection is the reason for the high CRP level.
What should I do if my C-reactive protein is positive?
If by "positive" you mean it's at a high level, talk to your doctor. They may recommend lifestyle changes (diet and exercise) or taking a statin.