C - Reactive Protein (CRP)

Blood

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No Fasting Required

Details

Acute-phase reactant; rises rapidly with infection or inflammation, including sepsis or arthritis.

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C-Reactive Protein (CRP) - Comprehensive Medical Test Guide

Why is it done?
- Measures levels of C-reactive protein, an acute phase reactant protein produced by the liver in response to inflammation and infection in the body
- Detects and monitors systemic inflammation from various causes including bacterial infections, viral infections, rheumatologic diseases, and inflammatory conditions
- Assists in differentiating between bacterial and viral infections (bacterial infections typically show higher elevations)
- Ordered when patients present with fever, signs of infection, or suspected inflammatory conditions
- Used to assess cardiovascular disease risk and monitor inflammatory progression in chronic conditions
- Commonly performed during initial evaluation of acute illness and periodically during treatment to monitor response to therapy
Normal Range
- Reference Range: Less than 3.0 mg/L (or <3 mg/dL depending on laboratory)
- Units of Measurement: milligrams per liter (mg/L) or milligrams per deciliter (mg/dL)
- Normal Result: CRP level below 3.0 mg/L indicates minimal to no systemic inflammation; typical finding in healthy individuals without acute illness
- Borderline/Elevated: 3.0-10.0 mg/L suggests mild inflammation; may indicate early infection or mild inflammatory response
- Moderately Elevated: 10.0-50.0 mg/L indicates moderate inflammation; consistent with significant infection, inflammation, or tissue damage
- Markedly Elevated: Greater than 50.0 mg/L suggests severe infection, significant inflammation, or serious underlying disease requiring urgent investigation
- Note: Reference ranges may vary slightly between laboratories; always refer to the specific laboratory's reference values provided with test results
Interpretation
- Elevated CRP with Clinical Symptoms: Supports diagnosis of acute infection or inflammation; level correlates with severity of inflammatory response
- Very High Elevations (>100 mg/L): May indicate serious bacterial infection, sepsis, myocardial infarction, major trauma, or severe autoimmune disease; warrants urgent clinical evaluation
- Rapid Rise in Serial Measurements: Suggests worsening infection or inflammatory process; may indicate treatment failure or disease progression
- Declining CRP Trend: Indicates improving inflammatory response, effective antibiotic therapy, or resolution of acute illness
- Mild Elevation without Clear Cause: May suggest subclinical inflammation, early disease process, or response to minor infection; often requires clinical correlation and additional testing
- Factors Affecting Results: Age (natural increase with aging), pregnancy, oral contraceptives, hormone replacement therapy, smoking, obesity, acute stress, recent surgery, myocardial infarction, and malignancy can all elevate CRP levels
- High-Sensitivity CRP (hs-CRP): Alternative test used for cardiovascular risk assessment; values <1.0 mg/L (low risk), 1.0-3.0 mg/L (intermediate risk), >3.0 mg/L (high risk)
- Clinical Context is Critical: CRP is a non-specific marker; interpretation requires consideration of patient's symptoms, clinical examination, medical history, and other laboratory findings
Associated Organs
- Primary Source - Liver: Hepatocytes synthesize and release CRP in response to interleukin-6 and other inflammatory cytokines
- Immune System Response: CRP is part of innate immunity; elevated with B-lymphocyte, macrophage, and neutrophil activation
- Infections Associated with Elevated CRP: Respiratory tract infections, urinary tract infections, meningitis, endocarditis, sepsis, pneumonia, abscess, acute appendicitis, cholecystitis, and acute diverticulitis
- Inflammatory Conditions: Rheumatoid arthritis, systemic lupus erythematosus, inflammatory bowel disease (Crohn's disease and ulcerative colitis), vasculitis, and polymyalgia rheumatica
- Cardiovascular Conditions: Acute myocardial infarction, atherosclerosis, heart failure, and coronary artery disease show elevated CRP related to inflammatory component
- Tissue Damage and Malignancy: Myocardial infarction, pulmonary embolism, major trauma, burns, post-operative state, and malignancies (especially hematologic and lung cancers)
- Metabolic and Endocrine Disorders: Type 2 diabetes mellitus, obesity, metabolic syndrome, and hyperlipidemia associated with chronic low-grade elevation
- Complications of Elevated CRP: Uncontrolled inflammation may lead to organ dysfunction, sepsis, septic shock, disseminated intravascular coagulation (DIC), multi-organ failure, and increased mortality if underlying cause is not identified and treated
Follow-up Tests
- Erythrocyte Sedimentation Rate (ESR): Complementary inflammatory marker; both ESR and CRP elevated in infection and inflammation, though they may have different time courses
- Complete Blood Count (CBC): To assess for leukocytosis, lymphocytosis, or other abnormalities suggesting infection or hematologic disease
- Blood Cultures: If bacteremia or sepsis suspected; CRP elevation may prompt blood culture collection for diagnosis
- Procalcitonin: More specific for bacterial infection; helps differentiate bacterial from viral infection when CRP is mildly elevated
- Imaging Studies: Chest X-ray, abdominal ultrasound, or CT scan may be indicated based on clinical presentation and elevated CRP to identify source of infection or inflammation
- Autoimmune Serologies: Antinuclear antibody (ANA), rheumatoid factor (RF), anti-CCP, and complement levels if autoimmune disease suspected
- Liver Function Tests: To assess hepatic synthetic function and evaluate for underlying liver disease contributing to inflammation
- Lipid Panel and Glucose: For cardiovascular risk assessment when CRP used as a risk marker
- Serial CRP Measurements: Repeat CRP testing at 24-48 hour intervals during acute illness to monitor disease progression or response to therapy; typically shows decline with successful treatment
- Tissue-Specific Biomarkers: Troponin (myocardial infarction), amylase/lipase (pancreatitis), or D-dimer (pulmonary embolism) based on clinical suspicion
Fasting Required?
- Fasting Required: No
- Food and Drink: Fasting is not required; CRP levels are not affected by recent food or fluid intake, so normal diet and hydration prior to testing is acceptable
- Medications: Continue all regularly prescribed medications unless specifically instructed otherwise by healthcare provider; NSAIDs, corticosteroids, antibiotics, and statins may affect CRP levels but should not be discontinued without medical guidance
- Timing Considerations: Morning collection is often preferred but not strictly required; time of day may slightly affect CRP levels (circadian variation exists)
- Physical Activity: Vigorous exercise and physical stress may temporarily elevate CRP; light activity is not contraindicated
- Smoking and Stress: Smoking and acute emotional stress can elevate CRP; avoid smoking for several hours before testing if possible, though this is not a strict requirement
- Blood Draw Procedure: Simple venipuncture; typically 5-10 mL of blood collected in standard serum separator tube (SST) or EDTA tube; no special handling required
- Results Timeline: Results typically available within 24 hours; urgent/stat testing may provide results within 1-4 hours in hospital settings

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