What is the difference between C-Reactive Protein (CRP) and Erythrocyte Sedimentation Rate (ESR)?

Differences Between CRP and ESR

CRP is a more specific and responsive marker of acute inflammation produced by the liver, while ESR is a slower-responding, less specific measure of blood viscosity affected by multiple non-inflammatory factors. 1

Basic Characteristics

C-Reactive Protein (CRP)

• Protein produced by the liver in direct response to inflammation 2
• Sensitivity of 73% and specificity of 78% for detecting organic disease 2
• Rises rapidly (within hours) in response to inflammation
• Returns to normal quickly after resolution of inflammation 3
• More specific marker for acute inflammatory processes 1

Erythrocyte Sedimentation Rate (ESR)

• Measure of blood viscosity as a surrogate marker of inflammation 2
• Sensitivity ranges from 54-78% and specificity from 46-95% 2
• Rises more slowly (24-48 hours) after onset of inflammation
• Remains elevated for longer periods after inflammation resolves 3
• Affected by multiple non-inflammatory factors 1

Key Differences

Response Time

• CRP: Rises within 4-6 hours of inflammatory stimulus, peaks at 24-48 hours
• ESR: Rises more slowly, taking 24-48 hours to increase significantly 3

Resolution Time

• CRP: Half-life of approximately 19 hours, normalizes quickly with resolution of inflammation
• ESR: Has a much longer half-life, may remain elevated for weeks after inflammation resolves 3, 1

Factors Affecting Results

ESR is affected by numerous non-inflammatory factors:

• Age and gender
• Anemia (increases ESR)
• Immunoglobulins and rheumatoid factor levels
• Pregnancy (increases ESR)
• Plasma protein abnormalities 4, 1

CRP is less affected by non-inflammatory factors but can be influenced by:

• Obesity
• Liver failure (may decrease CRP production)
• Certain medications 1

Clinical Interpretation

CRP	ESR	Clinical Interpretation
Elevated	Normal	Acute inflammation (early infection, early flare)
Normal	Elevated	Chronic inflammation, autoimmune diseases, or non-inflammatory factors affecting ESR
Elevated	Elevated	Active inflammation (both acute and chronic processes)
Normal	Normal	Low likelihood of significant inflammation [1]

Discordance Between Tests

• Discordance between ESR and CRP occurs in approximately 28-33% of cases 4, 5
• When discordant, CRP is generally a better measure of active inflammation 4
• Common patterns of discordance:
  • Elevated ESR/normal CRP: Often seen in resolving inflammation (32%), conditions with non-inflammatory ESR elevation (28%), or unexplained causes (32%) 5
  • Normal ESR/elevated CRP: Usually indicates active inflammatory disease (false-negative ESR) 5

Clinical Applications

When to Use CRP

• Acute inflammatory conditions
• Monitoring response to therapy in acute settings
• When rapid changes in inflammation need to be detected
• Initial diagnosis of inflammatory conditions 3, 1

When to Use ESR

• Monitoring chronic inflammatory conditions
• Conditions where ESR has specific diagnostic value (e.g., giant cell arteritis, polymyalgia rheumatica)
• When assessing overall disease severity rather than acute inflammation 4, 1

Best Practice Recommendations

• CRP should be the preferred test for detecting acute phase inflammation in patients with undiagnosed conditions 6
• Joint measurement of ESR and CRP is generally unwarranted in hospital practice 5
• When an inflammatory disorder is suspected, priority should be given to CRP due to its greater specificity 5
• In chronic inflammatory conditions, both tests may provide complementary information 4

Common Pitfalls

• Assuming low CRP rules out all inflammatory conditions
• Dismissing elevated ESR when CRP is normal (may indicate chronic inflammation)
• Treating the marker rather than the underlying condition
• Ignoring clinical context when interpreting results 1
• Ordering both tests routinely without clear clinical indication 6