What labs are recommended to assess an inflammatory response?

Recommended Laboratory Tests for Assessing Inflammatory Response

C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are the primary laboratory tests recommended for assessing inflammatory response, with CRP being the preferred first-line test due to its superior analytical characteristics and established clinical utility. 1

Primary Inflammatory Markers

C-Reactive Protein (CRP)

• First-line test for inflammatory assessment 1
• More sensitive for acute inflammation and responds quickly to changes (rises within 4-6 hours)
• Better for monitoring response to therapy
• Interpretation guidelines:
  • <1.0 mg/L: Low risk/minimal inflammation
  • 1.0-3.0 mg/L: Average risk/moderate inflammation

  • 3.0 mg/L: High risk/significant inflammation

  • 10 mg/L: Suggests acute infection or significant inflammation requiring investigation 1

• High-sensitivity CRP (hs-CRP) is specifically recommended for cardiovascular risk assessment 1

Erythrocyte Sedimentation Rate (ESR)

• Indirect measure of fibrinogen and other acute phase proteins
• Rises more slowly and remains elevated longer than CRP
• Better for monitoring chronic inflammatory conditions 1, 2
• Affected by factors such as renal disease, female sex, and older age 3
• Particularly valuable in detecting low-grade bone infections and monitoring certain autoimmune diseases 1, 3

Additional Inflammatory Markers

Complete Blood Count

• White blood cell (WBC) count with differential provides information about the type of inflammation 1
• Neutrophilia suggests bacterial infection
• Lymphocytosis suggests viral infection or certain chronic inflammatory conditions

Fibrinogen

• Acute phase protein associated with cardiovascular disease risk
• Has a longer half-life than CRP 1

Specialized Inflammatory Markers

• Fecal calprotectin: For intestinal inflammation 1, 4
• Serum amyloid A (SAA): Acute phase protein elevated in inflammatory conditions 1
• Disease-specific markers:
  • Rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA): For rheumatoid arthritis 1
  • Anti-nuclear antibodies (ANA): For autoimmune conditions 4

Interpretation of Combined Inflammatory Markers

CRP	ESR	Interpretation
Elevated	Normal	Acute inflammation (e.g., infections, early inflammation)
Normal	Elevated	Chronic inflammation (e.g., autoimmune diseases, stroke)
Elevated	Elevated	Active inflammation (both acute and chronic processes)
Normal	Normal	Low likelihood of significant inflammation [1]

Clinical Considerations

When to Order Both CRP and ESR

• Discordance between CRP and ESR occurs in approximately 12% of patients 5
• High CRP/low ESR pattern: Associated with acute infections, urinary tract infections, gastrointestinal infections, pneumonia, and myocardial infarction 5
• High ESR/low CRP pattern: Associated with connective tissue diseases, bone/joint infections, and ischemic stroke 5

Limitations and Pitfalls

• Neither test is specific for a particular disease
• CRP can be elevated in non-infectious conditions like obesity 1
• ESR has more false positive and false negative results than CRP 3
• Do not dismiss elevated ESR when CRP is normal, as this pattern can occur in several serious conditions 1
• Treat the underlying cause of inflammation, not the elevated marker itself 1
• Always interpret inflammatory markers in clinical context 1

Monitoring Recommendations

• For optimal assessment, obtain samples when the patient is metabolically stable 1
• Consider two measurements (optimally 2 weeks apart) for a stable estimate 1
• Monitor inflammatory markers approximately 4 weeks after initiating therapy 1

Disease-Specific Recommendations

Inflammatory Bowel Disease

• CRP and fecal calprotectin are recommended for assessment and monitoring 4
• Consider routine laboratory investigations including complete blood count, liver profile, albumin, and iron studies 4

Inflammatory Arthritis

• Consider autoimmune blood panel including ANA, RF, anti-CCP, ESR, and CRP 4
• Monitor with serial examinations including inflammatory markers every 4-6 weeks after treatment initiation 4

Suspected Bone/Joint Infection

• Both ESR and CRP should be assessed, as discordance may occur 6
• ESR has particular value in detecting low-grade bone infections 3

By following these recommendations for inflammatory marker testing, clinicians can effectively assess inflammatory responses and monitor treatment outcomes while avoiding common pitfalls in interpretation.