High-sensitivity C-reactive Protein (hs-CRP)
No current consensus exists on when to get tested; hs-CRP is often ordered in conjunction with other tests that are performed to assess risk of heart disease, such as a lipid panel (cholesterol, triglycerides, HDL-C, LDL-C) when your healthcare provider would like additional information on your risk.
A blood sample drawn from a vein in your arm
No test preparation is needed; however, you may be instructed to fast for 9-12 hours before the blood sample is taken if a lipid panel also is going to be done at the same time. You should be healthy at the time of the sample collection, without any recent illnesses, infections, inflammation, or injuries.
C-reactive protein (CRP) is a protein that increases in the blood with inflammation and infection as well as following a heart attack, surgery, or trauma. Studies have suggested that a persistent low level of inflammation plays a major role in atherosclerosis, the narrowing of blood vessels due to build-up of cholesterol and other lipids, which is often associated with cardiovascular disease (CVD). The hs-CRP test accurately measures low levels of CRP to identify low but persistent levels of inflammation and thus helps predict a person's risk of developing CVD.
There are two different tests that measure CRP and each test measures a different range of CRP level in the blood for different purposes:
- The standard CRP test measures markedly high levels of the protein to detect diseases that cause significant inflammation. It measures CRP in the range from 10 to 1000 mg/L. This test may be used to detect inflammation (see the article C-Reactive Protein).
- The hs-CRP test accurately detects lower levels of the protein than the standard CRP test. It measures CRP in the range from 0.5 to 10 mg/L. This test is used to evaluate individuals for risk of CVD.
CVD causes more deaths in the U.S. each year than any other cause, according to the American Heart Association. A number of risk factors, such as family history, high cholesterol, high blood pressure, being overweight or diabetic, have been linked to the development of CVD, but a significant number of people who have few or no identified risk factors will also develop CVD. This fact has lead researchers to look for additional risk factors that might be either causing CVD or that could be used to determine lifestyle changes and/or treatments that could reduce a person's risk.
High-sensitivity CRP is one of a growing number of cardiac risk markers that are used to help determine a person's risk. Some studies have shown that measuring CRP with a highly sensitive assay can help identify the risk level for CVD in apparently healthy people. This more sensitive test can measure CRP levels that are within the higher end of the reference range. These normal but slightly high levels of CRP in otherwise healthy individuals can predict the future risk of a heart attack, stroke, sudden cardiac death, and peripheral arterial disease, even when cholesterol levels are within an acceptable range.
hs-CRP could be a marker not only in apparently healthy people, recent studies have shown. Adults with congenital heart disease (ACHD) with elevated CRP have worse functional status and exercise capacity, greater risk for death, or non-elective cardiovascular hospitalization.
How is the test used?
A high-sensitivity C-reactive protein (hs-CRP) test measures low levels of CRP and may be used to help evaluate an individual for risk of cardiovascular disease (CVD). It may be used in combination with a lipid panel or with other cardiac risk markers, such as a lipoprotein-associated phospholipase A2 (Lp-PLA2) test, to provide added information about heart disease risk.
This test is different than the standard CRP test that is used to detect inflammation. For details, see the article on C-Reactive Protein (CRP).
High-sensitivity CRP is thought by some experts to be a useful test for determining risk of CVD, heart attacks, and strokes and that hs-CRP can play a role in the evaluation process before a person develops one of these health problems. Some say that the best way to predict risk is to combine a good marker for inflammation, like hs-CRP, with the lipid panel. Several groups have recommended that this test be used for people who have a moderate risk of heart attack over the next 10 years.
However, not all health professionals agree on hs-CRP's usefulness. Clinical trials that involve measuring hs-CRP levels are currently underway in an effort to better understand its role in cardiovascular events. These studies will help to form and refine guidelines on its use in screening and treatment decisions.
Recently, the U.S. Preventive Service Task Force (USPSTF) concluded in their "Risk Assessment for Cardiovascular Disease With Nontraditional Risk Factors: US Preventive Services Task Force Recommendation Statement" that there was no evidence that adding hs-CRP will benefit nor harm the traditional risk assessment for cardiovascular diseases in asymptomatic adults to prevent CVD event and initiation of preventative therapy.
When is it ordered?
Currently, there is no consensus on when to get tested, though some guidelines include recommendations on hs-CRP testing. For example, a guideline from the American College of Cardiology Foundations and the American Heart Association says that hs-CRP testing may be useful when men 50 years old or younger and women 60 years old or younger have intermediate risk. It also may be useful for treatment decisions when men and women are older than these respective ages and have LDL-C less than 130 mg/L and meet several other criteria, such as no existing heart disease, diabetes, kidney disease, or inflammatory conditions.
When hs-CRP is evaluated, it may be repeated to confirm that a person has persistent low levels of inflammation. The CDC and the American Heart Association (AHA) recommend that measurement of hs-CRP greater than 10 mg/L be repeated twice, optimally two weeks apart, fasting or non-fasting in patients free of infection or acute illness.
What does the test result mean?
Relatively high levels of hs-CRP in otherwise healthy individuals have been found to be predictive of an increased risk of a future heart attack, stroke, sudden cardiac death, and/or peripheral arterial disease, even when cholesterol levels are within an acceptable range.
People with higher hs-CRP values have the highest risk of cardiovascular disease and those with lower values have less risk. Specifically, individuals who have hs-CRP results at the high end of the normal range have 1.5 to 4 times the risk of having a heart attack as those with hs-CRP values at the low end of the normal range.
The American Heart Association and U.S. Centers for Disease Control and Prevention have defined risk groups as follows:
- Low risk: less than 1.0 mg/L
- Average risk: 1.0 to 3.0 mg/L
- High risk: above 3.0 mg/L
These values are only a part of the total evaluation process for cardiovascular diseases. Additional risk factors to be considered are elevated levels of cholesterol, LDL-C, triglycerides, and glucose. In addition, smoking, high blood pressure (hypertension), and diabetes also increase the risk level.
Is there anything else I should know?
Taking nonsteroidal anti-inflammatory drugs (NSAIDs, e.g., aspirin, ibuprofen, and naproxen) or statins may reduce CRP levels in blood. Both anti-inflammatory drugs and statins may help to reduce inflammation, thus reducing CRP.
Women on hormone replacement therapy have been shown to have elevated hs-CRP levels.
Since the hs-CRP and CRP tests measure the same protein, people with chronic inflammation, such as those with arthritis, should not have hs-CRP levels measured. Their CRP levels will already be very high due to the arthritis, so results of the hs-CRP test will not be meaningful.
Is hs-CRP specific for predicting heart disease?
No. CRP is a marker of inflammation, a process that can affect a number of organ systems. Most studies to date have focused on heart disease, but new research shows that having CRP in the high normal range may also be associated with other diseases such as colon cancer, complications of diabetes, and obesity.
I have had cholesterol tests but never an hs-CRP test. Why?
What is the difference between regular CRP and hs-CRP tests?
Both tests measure the same protein in the blood. The hs-CRP test is for apparently healthy people to determine their risk of cardiovascular disease. It measures CRP in the range from 0.5 to 10 mg/L. The CRP test is ordered to evaluate people who have signs and symptoms of a serious bacterial infection or of a serious chronic inflammatory disease such as rheumatoid arthritis. It measures CRP in the range from 10 to 1000 mg/L.