High Sensitivity C-Reactive Protei... Health Article

Definition

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.

Origins

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.

Benefits

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.

Description

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.