High Sensitivity C-Reactive Protein Test
The high sensitivity C-reactive protein (hsCRP) test is a blood assay used to estimate an individual's risk for heart disease and stroke. The test also measures the presence of inflammation or infection.
In the late twentieth century, the primary methods of measuring a person's risk of heart disease included traditional factors such as age, family history of heart disease or stroke, past heart disease, smoking, obesity, and tests that measured lipids in the bloodstream, including lowdensity lipoprotein (LDL). Low-density lipoproteins ("bad" cholesterol) were previously considered the gold standard in risk factor prediction.
In the 1990s and early twenty-first century, several new tests came into widespread use. These tests are considered better predictors of heart disease risk. They include blood tests to measure the levels of homocysteine, lipoprotein(a), fibrinogen, and highly sensitive C-reactive protein. They are called emerging or nontraditional risk factors.
Knowing one's highly sensitive C-reactive protein levels can help a person manage and lower his or her risk for heart disease. Factors that lower highly sensitive CRP levels include weight loss, regular exercise, a healthy diet, and smoking cessation. Medicines may also be needed. Medications include a class of drugs called statins, with brand names such as Lipitor, Zocor, Crestor, and Pravachol. Other interventions may include Zetia, a cholesterol absorption inhibitor, and a class of drugs called thiazoladinediones, such as the diabetes brandname medications Avandia and Actos.
According to the American Heart Association, the three risk levels associated with high sensitivity CRP levels are:
- Low risk: under 1 milligram per liter of blood.
- Average risk: 1 to 3 milligrams per liter of blood.
- High risk: More than 3 milligrams per liter of blood.
C-reactive protein is produced by the liver and is not normally found in the blood in high amounts. It is rapidly produced following an injury, bacterial or fungal infection, or inflammation. It disappears quickly once the injury, illness, or inflammation heals or resolves. High CRP levels following surgery or an injury are a good indication that an infection is present. Until early in this century, the blood test used to detect CRP levels could only measure them down to 3 milligrams per liter of blood or higher. Improvements in technology have permitted more precise measurements of CRP levels ranging from less than 0.3 milligrams to 3 milligrams per liter of blood. The more precise measurement is called the high sensitivity C-reactive protein (hsCRP) test.
While levels under 3 milligrams per liter of blood do not necessarily indicate the presence of infection, they do indicate the presence of an inflammatory reaction. Researchers found that these lower amounts of CRP in the body are extremely useful in predicting coronary heart disease (CHD). However, since CRP levels vary on different days, at least two separate measurements are needed to adequately determine a person's CHD risk level.
To take the high sensitivity CRP test, a healthcare worker draws blood from a vein, into a tube. In the laboratory, the tube of blood spins at high speed within a machine called a centrifuge. The blood cells sink to the bottom and the liquid stays on the top. This straw-colored liquid on the top is the plasma. To measure the high sensitivity CRP, a person's plasma is combined with other substances. From the resulting reaction, the amount of CRP in the plasma is determined.
A study released in 2003 by the College of American Pathologists found varying outcomes when it compared results from five different methods in identifying hsCRP. A 2001 study by several university medical departments found that six out of nine hsCRP testing methods did not produce results as accurate as the manufacturers claimed. In 2003 the Centers for Disease Control and Prevention announced that it would attempt to address these issues.
Unlike some blood tests that require fasting, the high sensitivity C-reactive protein test can be done either before or after eating. No other preparations are needed.
Each high sensitivity CRP test requires a 5-milliliter blood sample. A healthcare worker usually ties a tight band (tourniquet) on the person's upper arm. The blood is drawn from a vein in the arm, usually at the inside of the elbow or on the back of the hand. The needle insertion site is cleaned with antiseptic. A small needle is inserted through the skin and into the vein, allowing the blood sample to flow into a collection tube or syringe. Once the blood is collected, the needle is removed from
The primary risk to the patient is a mild stinging or burning sensation during the drawing of blood, with minor swelling or bruising afterward. Some patients may feel faint or lightheaded when blood is drawn.
There are generally no side effects associated with the test. Any weakness, fainting, sweating, or other unusual reaction should be immediately reported.
Research & general acceptance
Several large-scale scientific studies have shown that high sensitivity C-reactive protein levels are a strong predictor of future heart attacks and strokes among apparently healthy men and women. Research has also shown that hsCRP test will play an important role in preventing heart disease, according to an article in the March 2001 issue of Circulation. The Centers for Disease Control and Prevention, and the American Heart Association, recommend limited use of hsCRP testing for assessing heart disease risk. The two groups recommend the test only when a physician is undecided about a course of treatment for a patient who is considered at intermediate risk for CHD. According to an article in the February 2003 issue of the Harvard Health Letter, a growing number of physicians believe everyone should be tested, and this test may eventually supplant cholesterol testing as a predictor of CHD.
Training & certification
Nurses are usually the health care professionals that administer high sensitivity CRP tests. Nurses can also help educate patients regarding the role that a proper diet and regular exercise can play in reducing the risk of CHD. However, only a physician can recommend specific treatment and prescribe needed medication.
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American Heart Association National Center. 7272 Greenville Avenue, Dallas, TX 75231-4596. 800-242-8721. <http://www.americanheart.org>.
Ken R. Wells