Reference Range
The reference ranges for C-reactive protein (CRP) and high-sensitivity CRP (hs-CRP) are as follows. [1]
Normal findings: < 1.0 mg/dL or < 10.0 mg/L (SI units)
Cardiac risk:
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Low: < 1.0 mg/dL
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Average: 1.0-3.0 mg/dL
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High: > 3.0 mg/dL
hs-CRP: < 3 mg/L
Interpretation
Relative risk of future cardiovascular events based on hs-CRP testing is estimated as follows: [2]
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Low risk: CRP < 1.0 mg/L
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Intermediate risk: CRP 1.0-3.0 mg/L
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High risk: CRP > 3.0 mg/L
Acute inflammation is a CRP greater than 10.0 mg/L.
Relative risk in the high-risk group is estimated to be twice that in the low-risk group.
Collection and Panels
Specifics for collection and panels are as follows:
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Specimen type: Blood serum
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Container: Vacutainer, red top (preferred; see image below) or red/black top
Red-top vacutainer tube.
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Collection method: Venipuncture
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Specimen volume: 0.5 mL
Other instructions are as follows:
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Collect fasting specimen if lipid profile tested concurrently.
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Use the lower of 2 readings obtained at least 2 weeks apart to estimate stable CRP value.
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Avoid testing individuals who are metabolically unstable; have had a recent illness, tissue injury, or infection; or have other any general inflammation, acute or chronic.
Related tests are as follows:
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Lipid profile
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Lipoprotein-associated phospholipidase A2 (Lp-PLA2)
Background
Description
CRP is an acute-phase reactant synthesized by the liver in response to cytokines released by damaged tissue. Production is controlled by interluekin-6, an inflammatory cytokine. CRP is commonly measured to screen for inflammation or infection. Also, CRP is produced by cells in the vascular wall such as endothelial cells, smooth muscle cells, and also by adipose tissue.
Chronic inflammation is pivotal in heart disease; studies have shown that high levels of CRP, measured by high-sensitivity CRP (hs-CRP), can be a marker of atherosclerosis. hs-CRP is an important predictor for cardiovascular events including myocardial infarction, cerebrovascular events, peripheral vascular disease, and sudden cardiac death in individuals without a history of heart disease. In patients with acute coronary disease, CRP level predicts mortality and cardiac complications. High CRP levels portend a worse prognosis in patients with acute coronary syndromes. hs-CRP is also a marker of metabolic syndrome. [3]
Traditional assays for CRP are insufficiently sensitive for measuring the lower serum values associated with atherosclerotic disease. The newer hs-CRP assays are capable of measuring serum CRP to below 0.6 mg/dL.
High-sensitivity CRP testing has been shown to add to the predictive value of total cholesterol, low-density lipoprotein (LDL), and high-density lipoprotein (HDL), as well as the Framingham 10-year risk score.
Indications/Applications
Indications for hs-CRP testing include the following:
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Assessing the risk of cardiovascular disease or ischemic events in asymptomatic individuals to determine strategy for prevention of cardiovascular events
More specific recommendations from the American College of Cardiology Foundation and the American Heart Association on the use of hs-CRP testing in the assessment of cardiovascular risk in asymptomatic adults include the following: [8]
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hs-CRP testing may be useful in selecting patients for statin therapy in men 50 years and older or women 60 years and older with LDL less than 130 mg/dL who are not on lipid-lowering, hormone replacement, or immunosuppressant therapy, who are without clinical CHD, diabetes, chronic kidney disease, severe inflammatory conditions, or contraindications to statins.
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hs-CRP testing may be reasonable for cardiovascular risk assessment in asymptomatic men 50 years and older or women 60 years and older at intermediate risk (eg, based on Framingham Risk Score).
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hs-CRP testing has not been shown to be beneficial for cardiovascular risk assessment and is not recommended in asymptomatic high-risk individuals.
Considerations
Oral contraceptives may increase serum CRP.
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Red-top vacutainer tube.
