C-Reactive Protein (CRP) Test

Diagram of healthy and unhealthy ranges for C-reactive protein (CRP)

• C-reactive protein (CRP) is a blood test marker for inflammation in the body. CRP is produced in the liver and its level is measured by testing the blood.
• CRP is classified as an acute phase reactant, which means that its levels will rise in response to inflammation.
• Other common acute phase reactants include the erythrocyte sedimentation rate (ESR) and blood platelet count.

There are no signs or symptoms that are specific for an elevated C-reactive protein level because it is not a specific test. Signs or symptoms, if present, would depend on the underlying inflammatory condition that is the cause of the elevated CRP level.

In general, the main causes of increased CRP and other markers of inflammation are a variety of conditions, including

• burns,
• trauma,
• infections, such as pneumonia or tuberculosis,
• heart attack,
• chronic inflammatory diseases such as lupus, vasculitis, or rheumatoid arthritis,
• inflammatory bowel disease, and
• certain cancers.

C-reactive protein is a marker of inflammation and is typically not detected in the blood unless some degree of inflammation is present in the body.

C-reactive protein is a marker of inflammation and is typically not detected in the blood unless some degree of inflammation is present in the body.

• CRP measurement is made using a blood sample from a vein. The sample is then taken to a laboratory and analyzed.
• The traditional CRP measurement is often used to detect inflammation in the body. Your health-care provider may order a C-reactive protein level to check for flare-ups of inflammatory diseases such as rheumatoid arthritis, lupus, or vasculitis or to monitor whether anti-inflammatory medications are working to treat a disease or condition.
• Currently, a more highly sensitive measurement to detect CRP is used for cardiovascular risk assessment. This high-sensitive C-reactive protein is termed hs-CRP.
• Because measuring CRP levels at any point in time may be influenced by any infection or inflammation in the body, onetime measurement is generally not regarded as an adequate predictor of cardiovascular risk. Therefore, the U.S. Centers for Disease Control and Prevention (CDC) recommends checking two separate CRP levels approximately two weeks apart and using the average number of the two readings for cardiovascular risk assessment and screening purposes.

Checking the CRP level for the entire adult population is not recommended. Some experts recommend checking the serum CRP level routinely along with the cholesterol level; however, although this is not widely accepted.  Ideally, for cardiac risk testing, it is advisable to use the average between two separate CRP levels drawn two weeks part.

More importantly, the CRP level can provide additional information about an individual's cardiovascular risk in conjunction with other known cardiac risk factors, such as,

• diabetes mellitus,
• high blood pressure,
• high cholesterol, obesity,
• age, and
• smoking cigarettes.

The treatment of an elevated CRP in the context of cardiovascular disease, in and of itself, may be meaningless. Instead, appropriate treatment and prevention of the underlying risks and conditions need to be the primary focus of cardiovascular risk reduction.

The most effective and reliable ways to reduce many cardiac factors are

• regular exercise,
• a balanced diet, and
• cigarette smoking cessation.

In individuals with elevated cholesterol levels who do not reach their target cholesterol level with

• diet modifications, 
• exercise, and
• cholesterol-lowering medication.

People with elevated C-reactive protein levels may be advised by their treating doctors. Statin drugs (such as simvastatin [Zocor], atorvastatin [Lipitor], etc.) are at the forefront of the recommended cholesterol-lowering agents. Lowering of CRP may be seen with the use of statin drugs even without significant improvement of the cholesterol profile.

Reduction of CRP level has also been noted in individuals with known cardiovascular disease who begin aspirin therapy. In those without known cardiovascular disease or significant risk factors for it, aspirin use is not generally recommended. Some diabetic medications (thiazolidinediones) have also been shown to reduce CRP levels in people with or without diabetes mellitus. This effect was seen independent of their glucose-lowering effects.

The overall outlook for those with an elevated CRP largely depends on the cause. In general, the level may be elevated as a response to any inflammation or infection present in the body. The outlook will depend on the success of treatment directed at the underlying cause of the inflammation.

More specifically, as a risk assessment tool for cardiovascular disease, the elevation of CRP correlates with the presence of the traditional cardiac risk factors including,

• hypertension (high blood pressure),
• high cholesterol,
• diabetes mellitus,
• obesity,
• advanced age,
• cigarette smoking, and
• strong family history of cardiac disease.
• Appropriate medical management of these risk factor include
• diet,
• exercise,
• smoking cessation, and

Medical treatment and management of the risk factors for elevated C-reactive protein blood levels are important to prevent future cardiovascular disease.

According to the American Heart Association (AHA) and the CDC, the following guidelines are recommended for the assessment of cardiovascular risk in regards to high-sensitivity C-reactive protein (hs-CRP) levels:

• Low risk for cardiovascular disease if hs-CRP is 1 milligram (mg) per liter or less
• Moderate risk for cardiovascular disease if hs-CRP is between 1 and 3 mg per liter
• High risk for cardiovascular disease if hs-CRP greater than 3 mg per liter

CRP level of greater than 10 mg per liter may be seen in an acute plaque rupture such as a heart attack or stroke, provided there is no other explanation for the elevated level (other inflammatory or infectious process).

Because of the inflammatory component of atherosclerosis, it may correlate with an elevated CRP level and has been linked with cardiovascular disease. However, based on the currently available data it cannot be considered an independent risk factor for cardiovascular disease.

The traditional risk factors for cardiovascular disease, including

• high blood pressure (hypertension),
• type 2 diabetes,
• elevated blood cholesterol,
• age,
• cigarette smoking use,
• obesity, and
• family history of heart disease.

According to recent studies, after adjusting for these traditional risk factors, elevated CRP level alone is unlikely to be a cause of cardiovascular disease.

Nevertheless, CRP may be used as a predictor of cardiovascular disease based on its correlation with the other known cardiac risk factors and their role in the formation of atherosclerosis. In individuals with some or all of these traditional risk factors, elevated CRP levels have been detected. Some data even suggest a trend of higher CRP elevation in the presence of a higher number of risk factors.

The elevation of CRP has also been linked to atherosclerosis and heart disease. Atherosclerosis, or cholesterol plaquing of the arteries, is known to have an inflammatory component that is thought to cause the rise in CRP levels in the blood. Atherosclerosis is also felt to be affected by age and other cardiovascular risk factors including diabetes mellitus, high cholesterol, high blood pressure, and cigarette smoking.

In atherosclerosis, the blood vessel wall becomes injured. This injury acts as a focus of inflammation and leads to the formation of plaques in the blood vessel walls. The plaques typically contain blood cells of inflammation, cholesterol deposits, and debris from the injured cells in the blood vessel lining. The accumulation of these elements leads to the narrowing of the wall of the blood vessel. The blood vessel narrowing can hinder the blood flow and the plaque can rupture and flake off the blood vessel wall causing blockage and leading to strokes and heart attacks.

The burden of plaques in the body can be proportional to the degree of CRP elevation in persons with atherosclerosis. Atherosclerotic plaques can exist in different stages throughout the body.