High-Sensitivity C-Reactive Protein: Reference Range, Interpretation, Collection and Panels

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 and smooth muscle cells and also by the adipose tissue. Chronic inflammation is pivotal in heart disease ; studies have shown that high CRP levels, measured by 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 levels predict 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. [ 5 ] 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 levels to below 0.6 mg/dL. hs-CRP testing has been shown to add to the predictive value of total cholesterol, 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: 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 [ 11 ] :

• hs-CRP levels are used to classify individuals into cardiovascular disease risk groups. Levels below 1 mg/L indicate low risk, levels in the range of 1-3 mg/L indicate moderate risk, and levels above 3 mg/L indicate high risk. [ 10 , 12 ]
• hs-CRP testing may be useful in selecting patients for statin therapy in males 50 years and older or females 60 years and older with LDL less than 130 mg/dL who are not on lipid-lowering, hormone replacement, or immunosuppressant therapy or do not have clinical coronary heart disease, diabetes, chronic kidney disease, severe inflammatory conditions; or do not have contraindications to statins.
• hs-CRP testing may be reasonable for cardiovascular risk assessment in asymptomatic males 50 years and older or females 60 years and older at intermediate risk (e.g., based on the Framingham Risk Score).
• hs-CRP testing has not been shown to be beneficial for cardiovascular risk assessment and is not recommended in asymptomatic high-risk individuals.

Cardiovascular disease applications

• Risk Assessment in Coronary Artery Disease (CAD) - hs-CRP is incorporated into advanced risk assessment algorithms, enhancing the prediction of cardiovascular events beyond traditional risk factors. [ 13 ]
• Acute Coronary Syndromes and Percutaneous Coronary Intervention (PCI) - In patients with CAD undergoing PCI, a high baseline hs-CRP level is a predictor of adverse clinical outcomes. A 2023 meta-analysis found that elevated hs-CRP levels were associated with an increased risk for major adverse cardiac events, all-cause mortality, cardiovascular mortality, and in-stent restenosis. [ 12 ]
• Diastolic Dysfunction - In geriatric patients, elevated hs-CRP levels have been significantly associated with the presence of diastolic dysfunction, suggesting its role in identifying inflammation-related cardiac changes in older adults. [ 14 ]

Cerebrovascular and neurological applications

• Intracranial Arterial Stenosis: Among older patients who have had a cerebral infarction, elevated hs-CRP levels are independently correlated with the presence of intracranial atherosclerotic stenosis. [ 15 ]
• General Noncommunicable Diseases: A 2022 review established hs-CRP as a key marker for a wide range of noncommunicable diseases, including stroke, cancer, and neurodegenerative conditions such as Parkinson's disease and Alzheimer's due to its role in chronic inflammation. [ 16 ]

Expanded indications

• Diabetic Retinopathy - A 2025 study demonstrated that hs-CRP levels progressively increase with the severity of diabetic retinopathy in patients with type 2 diabetes. After adjusting for other factors, each 1 mg/L increase in hs-CRP was associated with a 1.4-fold higher likelihood of having diabetic retinopathy. [ 17 ]
• Chronic Obstructive Pulmonary Disease (COPD) - A study conducted from December 2024 to March 2025 found that elevated hs-CRP levels are significantly associated with increased dyspnea, breathlessness severity, and more frequent exacerbations in patients with COPD. This positions hs-CRP as a valuable, low-cost biomarker to enhance risk stratification and personalize care, particularly in resource-constrained settings. [ 18 ]

Considerations

Several factors can influence CRP and hs-CRP test results. Elevated levels may be seen in individuals with hypertension, obesity, metabolic syndrome, diabetes mellitus, chronic infections such as bronchitis or gingivitis, chronic inflammatory conditions such as rheumatoid arthritis, and lipid abnormalities such as low HDL cholesterol or high triglycerides. Cigarette smoking can also raise CRP levels. Conversely, moderate alcohol intake, weight reduction, and regular physical activity are associated with lower CRP concentrations. [ 1 ] Taking oral contraceptives may also increase serum CRP levels.