What lab tests are needed to check for inflammation?

Laboratory Tests for Inflammation Assessment

C-reactive protein (CRP) is the primary inflammatory marker of choice, with erythrocyte sedimentation rate (ESR), complete blood count, and other specialized tests serving as complementary assessments depending on the clinical context. 1

Primary Inflammatory Markers

C-reactive Protein (CRP)

• High-sensitivity CRP (hs-CRP) is the preferred analyte due to its:
  • Better standardization and precision
  • Faster response to inflammatory changes (rises within 4-6 hours)
  • More rapid normalization after resolution of inflammation
  • Better correlation with acute inflammatory processes 1
• Interpretation guidelines:
  • Low risk/minimal inflammation: <1.0 mg/L
  • Average risk/moderate inflammation: 1.0-3.0 mg/L
  • High risk/significant inflammation: >3.0 mg/L
  • Values >10 mg/L suggest acute infection or significant inflammation 1, 2
• Collection protocol: Two measurements (fasting or non-fasting), optimally 2 weeks apart, with results averaged 1

Erythrocyte Sedimentation Rate (ESR)

• Rises more slowly and remains elevated longer than CRP
• Better for monitoring chronic inflammatory conditions 2, 3
• Affected by age, sex, anemia, and other non-inflammatory factors 4
• Particularly useful for:
  • Detecting low-grade bone infections
  • Monitoring systemic lupus erythematosus 4

Additional Laboratory Tests

Complete Blood Count (CBC)

• White blood cell count (WBC) with differential
  • Elevated in bacterial infections and inflammatory conditions
  • Specific patterns (neutrophilia, lymphocytosis, eosinophilia) can suggest different types of inflammation 1

Other Routine Laboratory Tests

• Albumin: Often decreased in chronic inflammation
• Liver profile: To assess liver involvement
• Iron studies: Inflammation can affect iron metabolism
• Renal function: To evaluate kidney involvement 1

Specialized Tests (Based on Clinical Suspicion)

• Fecal calprotectin: For intestinal inflammation 1
• Fecal lactoferrin: Alternative marker for intestinal inflammation 1
• Stool analysis and culture: To rule out infectious causes 1
• C. difficile toxin testing: When appropriate 1

Interpretation of Combined Inflammatory Markers

CRP	ESR	Interpretation
Elevated	Normal	Acute inflammation (e.g., early infection, myocardial infarction)
Normal	Elevated	Chronic inflammation (e.g., SLE, bone/joint infections)
Elevated	Elevated	Active inflammation (both acute and chronic processes)
Normal	Normal	Low likelihood of significant inflammation [2,5]

Clinical Pearls and Pitfalls

• CRP/ESR discordance occurs in approximately 12% of patients and can provide diagnostic clues 5:

  • High CRP/Low ESR: More common in urinary, gastrointestinal, lung, and bloodstream infections; myocardial infarction; venous thromboembolism
  • High ESR/Low CRP: More common in bone/joint infections, connective tissue diseases (especially SLE), and cerebrovascular events

• Important considerations:

  • Neither test is specific for any particular disease
  • Always interpret in clinical context
  • Do not dismiss elevated ESR when CRP is normal, as this pattern occurs in several serious conditions 2
  • Do not treat the marker itself; treat the underlying condition 2
  • Values may be affected by medications (e.g., statins lower CRP)
  • Obesity can elevate CRP independently of other inflammatory processes 2

• Follow-up testing:

  • For monitoring treatment response, repeat inflammatory markers after approximately 4 weeks of therapy 2
  • CRP is more useful for monitoring acute conditions
  • ESR is more useful for monitoring chronic conditions 6, 4

When assessing inflammation, begin with CRP and ESR, then add additional tests based on clinical presentation and suspected underlying conditions to optimize diagnostic accuracy and guide appropriate treatment decisions.