C-Reactive Protein (CRP)

A C-reactive protein (CRP) test is a blood test that measures the amount of a protein called C-reactive protein in your blood. C-reactive protein measures general levels of inflammation in your body.

High levels of CRP are caused by infections and many long-term diseases. But a CRP test cannot show where the inflammation is located or what is causing it. Other tests are needed to find the cause and location of the inflammation.

Why It Is Done

A C-reactive protein (CRP) test is done to:

• Check for infection after surgery. CRP levels normally rise within 2 to 6 hours of surgery and then go down by the third day after surgery. If CRP levels stay elevated 3 days after surgery, an infection may be present.
• Identify and keep track of infections and diseases that cause inflammation, such as:
  • Cancer of the lymph nodes (lymphoma).
  • Diseases of the immune system, such as lupus.
  • Painful swelling of the blood vessels in the head and neck (giant cell arteritis).
  • Painful swelling of the tissues that line the joints (rheumatoid arthritis).
  • Swelling and bleeding of the intestines (inflammatory bowel disease).
  • Infection of a bone (osteomyelitis).
• Check to see how well treatment is working, such as treatment for cancer or for an infection. CRP levels go up quickly and then become normal quickly if you are responding to treatment measures.

A special type of CRP test, the high-sensitivity CRP test (hs-CRP), may be done to find out if you have an increased chance of having a sudden heart problem, such as a heart attack. Inflammation can damage the inner lining of the arteries and make having a heart attack more likely. However, the connection between high CRP levels and heart attack risk is not very well-understood.

Results

A C-reactive protein (CRP) test is a blood test that measures the amount of a protein called C-reactive protein in your blood.

Normal

Normal values may vary from lab to lab. Results are usually available within 24 hours.

C-reactive protein (CRP)

Normal:	0–1.0 mg/dL or less than 10 mg/L (SI units)

Any condition that results in sudden or severe inflammation may increase your CRP levels.

Some medicines may decrease your CRP levels.

High-sensitivity C-reactive protein (hs-CRP) levels

The hs-CRP test measures your risk for heart problems. It may be done to find out if you have an increased chance of having a sudden heart problem, such as a heart attack. However, the connection between high CRP levels and heart attack risk is not very well-understood.

High-sensitivity C-reactive protein (hs-CRP) levels

Less than 1.0 mg/dL	Lowest risk
1.0 to 3.0 mg/dL	Average risk
More than 3.0 mg/dL	Highest risk

Many conditions can change CRP levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and medical history.

What To Think About

• High-sensitivity C-reactive protein (hs-CRP) measures very low amounts of CRP in the blood. This test may help find your risk for heart problems, especially when it is considered along other risk factors such as cholesterol, age, blood pressure, and smoking. But the connection between high CRP levels and heart disease risk is not understood very well.
• High CRP levels before a major surgery may indicate that you are at risk for developing an infection after surgery.
• CRP testing can be used to see how well you respond to cancer treatment or treatment for an infection. Your CRP levels will rise quickly and then quickly return to normal if the treatment is working.
• High CRP levels may increase your chances of having other diseases, such as age-related macular degeneration and colon cancer.