CRP (C-Reactive Protein)
Acute-phase protein as inflammation marker for infections and cardiovascular risk
Also known as
Definition
C-reactive protein (CRP) is an acute-phase protein produced in the liver in response to inflammatory stimuli — primarily driven by IL-6. Standard CRP (classic) is used for infection diagnostics; high-sensitivity CRP (hsCRP) measures subclinical inflammation and is an independent cardiovascular risk marker. CRP rises within 6–12 hours of inflammation onset and normalizes rapidly (half-life ~19 h) after resolution.
| Parameter | Value |
|---|---|
| Unit | mg/l |
| Reference Range | Standard CRP: < 5 mg/l (infection diagnostics) | hsCRP (cardiovascular risk): < 1 mg/l (low) | 1–3 mg/l (intermediate) | > 3 mg/l (elevated) |
Agree on your personal target range with your doctor.
↓ What a low value means
Very low CRP indicates no systemic inflammation. Your doctor interprets the result.
↑ What a high value means
Standard CRP > 5 mg/l: acute inflammation (infection, autoimmune disease, tissue injury). hsCRP 1–3 mg/l: intermediate cardiovascular risk; 3–10 mg/l: high risk and/or subacute inflammation. > 10 mg/l: severe inflammation or infection — NOT suitable for cardiovascular risk assessment.
✓ What can influence this value
CRP rises markedly with acute infections and inflammation and after injuries and surgery. Overweight (adipose tissue is pro-inflammatory), smoking, periodontitis, chronic diseases, and intense physical strain can also raise the value. A Mediterranean diet, regular exercise, and adequate sleep are associated with lower values. The assessment is made by the treating doctor.
When to test
hsCRP: cardiovascular risk screening (in intermediate-risk patients), metabolic syndrome, monitoring inflammatory conditions. The AHA/CDC scientific statement (Pearson 2003) describes two measurements about two weeks apart for risk assessment, outside acute infections. Standard CRP: infection diagnostics and monitoring.
Frequently asked questions
What is the difference between CRP and hsCRP? +
It is the same protein but with different assay methods and sensitivity ranges. Standard CRP measures in the mg/l range (infections: 10–500 mg/l). High-sensitivity CRP (hsCRP) measures down to 0.1 mg/l and is designed for subclinical inflammation and cardiovascular risk assessment.
Can gum disease really raise my CRP? +
Yes, significantly. Periodontitis is a chronic bacterial inflammation that substantially elevates systemic CRP (often > 2 mg/l). After periodontal treatment, hsCRP can fall measurably.
Is CRP a causal factor for heart disease or just a marker? +
Current evidence (Mendelian randomization studies) suggests CRP is primarily a marker of underlying inflammatory processes rather than a direct causal molecule. The elevated cardiovascular risk associated with high hsCRP likely reflects the underlying inflammation (e.g., atherosclerotic plaques, adipose tissue inflammation).
Does exercise permanently lower CRP? +
Regular moderate aerobic exercise is associated with lower hsCRP values in the long term. Acute intense exercise (marathon) transiently raises CRP substantially. Mechanism: exercise reduces visceral fat (IL-6 source), improves endothelial function, and increases anti-inflammatory cytokines.
CRP (C-Reactive Protein)
Sources
- Ridker PM et al. (2002) Comparison of C-Reactive Protein and Low-Density Lipoprotein Cholesterol Levels in the Prediction of First Cardiovascular Events. N Engl J Med.
- Pearson TA et al. (2003) Markers of Inflammation and Cardiovascular Disease: AHA/CDC Scientific Statement. Circulation.
- Pepys MB, Hirschfield GM (2003) C-reactive protein: a critical update. J Clin Invest.
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.