C-reactive protein (also referred to as CRP; High-sensitivity C-reactive protein; hs-CRP) is produced by the liver. CRP levels increase whenever there are instance of inflammation in the body. CRP was discovered in 1930 by Tillett and Francis in the serum of patients with acute inflammation.  

How the Test for C-reactive Protein is Performed

There is no preparation necessary for a C reactive protein test. Blood is taken from a vein on the inside of the elbow or the back of the hand. The sample is mixed with antiserum, a liquid that contains substances designed to find the specific protein. There is very little risk to having a CRP test. Side effects may include: Excessive bleeding, Fainting or feeling light-headed, Hematoma (blood accumulating under the skin) or infection at the injection site.  

How is the test for CRP used?

CRP testing is not precise enough to diagnose specific diseases but serves more as a general indicator that more testing may be needed if inflammation or infection is found. The CRP test is therefore useful in assessing patients with:

• Inflammatory bowel disease
• Some forms of arthritis
• Autoimmune diseases
• Pelvic inflammatory disease (PID)
• rheumatoid arthritis
• lupus
• Cancer
• Connective tissue disease
• Heart attack
• Infection
• Pneumococcal pneumonia
• Rheumatoid arthritis
• Rheumatic fever
• Tuberculosis

 Low CRP levels are not always an indication that there is no inflammation as levels may not always increase in persons with rheumatoid arthritis and lupus.  

The more sensitive form of the CRP test hs-CRP is used for screening persons who appear to be healthy for the following serious conditions:  

• Coronary heart disease (CHD)
• Cardiovascular disease

 High CRP levels are considered by some to be a risk factor for heart disease, but it is not clear whether CRP is only a sign of cardiovascular disease or if it actually an underlying cause of heart problems. The American Heart Association has developed the following in relation to cardiovascular health and CRP levels: 

• You are at low risk of developing cardiovascular disease if your hs-CRP level is lower than 1.0mg/L
• You are at average risk of developing cardiovascular disease if your levels are between 1.0 and 3.0 mg/L
• You are at high risk for cardiovascular disease if your hs-CRP level is higher than 3.0 mg/L

 The test is also performed in instances when there is a chance of severe inflammation occurring such as after surgery or to monitor the heeling of serious wounds,  burns or when there are large surgical incisions such as in the case of organ transplants and to ensure that anti-inflammatory medications are working correctly. CRP levels will fall as inflammation decreases, making the test an excellent means of monitoring patient recovery and detecting possible infections that would lead to serious complications. Simply put, if your doctor informs you that the CRP level in your blood has dropped, in all likelihood, you are getting better.  

Other factor can raise the levels of CRP in the blood such as pregnancy, use of birth control pills and hormone replacement therapy. Obese persons have also been found to have higher levels of CRP than those with healthy body weights.

 What is considered to be “Normal” CRP test results? 

Normally, there is no CRP detectable in the blood and all results should be discussed with a physician.