C-reactive protein (CRP) is a protein produced by the liver in response to inflammation. When inflammation occurs anywhere in the body, from infection, injury, autoimmune activity, or chronic disease, CRP levels in the blood rise rapidly. This makes CRP a sensitive marker of inflammation, useful for detecting and monitoring a wide range of conditions. Understanding your CRP result requires knowing which type of test was ordered (standard vs. high-sensitivity) and interpreting the value in clinical context.

Standard CRP vs. High-Sensitivity CRP (hs-CRP)

Standard CRP: Used to detect significant inflammation, from infections, flares of autoimmune disease, or serious injury. Normal range is typically below 1 mg/dL (10 mg/L), though some labs use below 0.5 mg/dL.

High-sensitivity CRP (hs-CRP): A more sensitive version of the same test, capable of detecting low-grade, chronic inflammation. It is used to assess cardiovascular risk in people who appear healthy. Values are reported in mg/L:

• Below 1.0 mg/L: Low cardiovascular risk
• 1.0-3.0 mg/L: Average cardiovascular risk
• Above 3.0 mg/L: Elevated cardiovascular risk

A very high hs-CRP (above 10 mg/L) usually suggests active infection or injury rather than cardiovascular risk, and a repeat should be done once any acute illness has resolved.

Common Causes of High CRP

1. Bacterial Infections

What it is: Bacterial infections cause the most dramatic rises in CRP, levels can reach 100-300 mg/L or higher in severe sepsis or bacterial pneumonia.

Why it happens: Bacteria trigger an intense innate immune response; CRP rises within hours of the onset of infection. The degree of elevation roughly correlates with the severity of infection and can help guide antibiotic treatment.

When to seek evaluation: Markedly elevated CRP with fever, localized pain, or signs of infection should prompt evaluation to identify and treat the source.

2. Autoimmune and Inflammatory Diseases

What it is: Chronic inflammatory conditions cause persistently elevated CRP, which reflects the degree of ongoing systemic inflammation.

Examples: Rheumatoid arthritis (CRP rises during flares), lupus (CRP may be elevated but is less sensitive than ESR in lupus), inflammatory bowel disease (Crohn's disease elevates CRP more than ulcerative colitis), vasculitis, polymyalgia rheumatica.

Clinical use: CRP is used alongside symptoms and other markers (ESR, specific antibodies) to monitor disease activity and response to treatment. A falling CRP suggests treatment is working; a rising CRP may signal a flare or infection.

3. Tissue Injury and Surgery

What it is: Any significant tissue damage, surgery, trauma, burns, or heart attack, triggers a CRP response as part of the acute phase reaction.

Why it happens: Tissue damage releases inflammatory signals (cytokines, particularly IL-6) that stimulate the liver to produce CRP within 6-8 hours. CRP peaks around 48-72 hours and then declines as healing progresses.

When to seek evaluation: A CRP that fails to fall after surgery or injury, or that rises again after initially declining, may indicate a complication (surgical site infection, wound dehiscence) requiring evaluation.

4. Cardiovascular Disease and Risk

What it is: Low-grade inflammation plays a key role in the development of atherosclerosis (arterial plaque). Elevated hs-CRP is an independent predictor of cardiovascular events (heart attack, stroke) beyond traditional risk factors.

Why it matters: People with low LDL but elevated hs-CRP (above 2 mg/L) may still benefit from statin therapy, which reduces both cholesterol and CRP. The JUPITER trial established this evidence base. hs-CRP is used as an adjunct to cardiovascular risk calculators when the decision to start treatment is uncertain.

Risk factors: Obesity, smoking, sedentary lifestyle, diabetes, hypertension, poor diet, all increase chronic low-grade inflammation and hs-CRP.

5. Obesity

What it is: Adipose tissue, particularly visceral (abdominal) fat, is metabolically active and produces inflammatory cytokines that continuously stimulate CRP production.

Why it matters: Obesity-related low-grade inflammation measured by hs-CRP is one mechanism linking excess weight to increased cardiovascular and metabolic disease risk. Weight loss consistently lowers hs-CRP.

6. Cancer

What it is: Many cancers are associated with elevated CRP due to tumor-associated inflammation. Elevated CRP is not used to diagnose cancer, but persistently elevated CRP without an identified infectious or inflammatory cause warrants investigation that may include cancer screening.

When to Seek Medical Care

Emergency, call 911 or go to the emergency room immediately if a high CRP occurs alongside any of these warning signs, which can point to a serious underlying complication:

• Chest pain, pressure, or tightness, especially with shortness of breath, sweating, or pain spreading to the arm or jaw (possible heart attack)
• Shortness of breath or difficulty breathing at rest
• High fever with confusion, a racing heart, very low blood pressure, or extreme weakness (possible sepsis)
• Fainting or loss of consciousness
• Sudden one-sided weakness, facial drooping, or slurred speech (possible stroke)
• A surgical or wound site with rapidly spreading redness, swelling, or pus, especially with fever or chills

See a doctor soon (non-urgent) for:

• An unexpectedly elevated CRP found on routine bloodwork with no acute symptoms
• A standard CRP result markedly above the normal range, to help identify the underlying cause
• Low-grade hs-CRP elevation (roughly 1-10 mg/L) found during cardiovascular risk assessment, to discuss whether it changes your treatment plan
• A CRP that fails to fall as expected after surgery or injury, without the emergency symptoms listed above
• Persistently elevated CRP with no clear infectious or inflammatory cause identified

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