C-reactive protein (CRP) is an acute phase protein produced by the liver in response to inflammation. Elevations occur with infections, autoimmune diseases, tissue injury, and other inflammatory conditions. The crp test comes in two forms: standard CRP for evaluating active inflammation, and high-sensitivity CRP (hs-CRP) for cardiovascular risk assessment. This guide covers both tests, normal ranges, and clinical applications.
Standard CRP vs hs-CRP
Both measure the same protein but with different sensitivities and clinical purposes:
Standard CRP: Detects elevations from active inflammation (infections, autoimmune flares, tissue injury). Lower limit of detection around 5-10 mg/L. Used to evaluate suspected infection or inflammatory disease.
hs-CRP: Detects much smaller elevations associated with chronic low-grade inflammation linked to cardiovascular risk. Lower limit of detection around 0.1 mg/L. Used for cardiovascular risk stratification.
Reference ranges
Standard CRP:
- Normal: under 10 mg/L
- Mild elevation: 10-100 mg/L
- Marked elevation: above 100 mg/L (suggests bacterial infection or severe inflammation)
hs-CRP for cardiovascular risk:
- Low risk: under 1.0 mg/L
- Moderate risk: 1.0-3.0 mg/L
- High risk: above 3.0 mg/L
Standard CRP clinical uses
- Suspected bacterial infection
- Monitoring inflammatory disease activity (rheumatoid arthritis, IBD, etc.)
- Post-surgical monitoring for infection
- Sepsis evaluation
- Differentiating bacterial from viral causes (less reliable)
Marked CRP elevation (above 100 mg/L) strongly suggests bacterial infection. Mild-moderate elevations have many causes.
hs-CRP cardiovascular risk
Chronic low-grade inflammation contributes to atherosclerosis. hs-CRP is one of several markers reflecting this. The JUPITER trial established that statins reduce cardiovascular events even in patients with normal LDL but elevated hs-CRP.
hs-CRP testing is most useful in patients at intermediate cardiovascular risk where additional information could change treatment decisions. The American Heart Association includes hs-CRP in selected risk assessment scenarios.
Causes of elevated CRP
- Bacterial infections
- Viral infections (often less marked elevation)
- Autoimmune diseases
- Tissue injury (trauma, surgery, MI)
- Cancer
- Obesity (chronic low-grade inflammation)
- Smoking
- Recent dental procedures
- Pregnancy
What CRP doesn’t tell you
CRP elevation is non-specific. It indicates inflammation but doesn’t identify the cause. CRP must be interpreted in clinical context with symptoms, physical findings, and other tests. Single CRP values without context are difficult to interpret.
Frequently Asked Questions
Should I check hs-CRP for cardiovascular risk?
Useful for intermediate-risk patients where additional information could change statin decisions. Not routinely recommended for all patients.
Can lifestyle change affect CRP?
Yes. Weight loss, exercise, smoking cessation, and Mediterranean diet reduce CRP.
What does mildly elevated CRP mean?
Many possible causes. Clinical context determines significance.
How does CRP differ from ESR?
Both inflammation markers. CRP responds faster than ESR. See our ESR test guide.
Is fasting required for CRP?
No fasting required.
The bottom line on CRP testing
CRP is a sensitive but non-specific inflammation marker. Standard CRP evaluates active inflammation; hs-CRP assesses cardiovascular risk. Both must be interpreted in clinical context. Discuss results with your healthcare provider for proper interpretation.