What lab tests are used to assess inflammation in the body?

Laboratory Tests for Assessing Inflammation in the Body

C-reactive protein (CRP) is the preferred primary inflammatory marker for clinical use due to its superior analytical characteristics, standardization, and established clinical utility. 1

Key Inflammatory Markers

First-Line Inflammatory Markers

1. C-reactive protein (CRP)

   • High-sensitivity CRP (hs-CRP) is the analyte of choice for cardiovascular risk assessment 1
   • Produced by liver in response to inflammation
   • Risk categories: low risk (<1.0 mg/L), average risk (1.0-3.0 mg/L), high risk (>3.0 mg/L) 1
   • Values >10 mg/L suggest acute infection or significant inflammation requiring investigation 1, 2
   • More sensitive for acute inflammation; responds quickly to changes 3, 4

2. Erythrocyte sedimentation rate (ESR)

   • Indirect measure of fibrinogen and other acute phase proteins
   • Rises slowly and remains elevated longer than CRP
   • Better for monitoring chronic inflammatory conditions 3, 4
   • Can be affected by age, sex, anemia, and renal disease 4

Second-Line Inflammatory Markers

1. White blood cell (WBC) count

   • Elevated in acute infections and inflammatory conditions 1
   • Differential count provides additional information about type of inflammation

2. Fibrinogen

   • Acute phase protein associated with cardiovascular disease risk 1
   • Has longer half-life than CRP 3

3. Serum amyloid A (SAA)

   • Acute phase protein that can be elevated in inflammatory conditions 1

Clinical Application of Inflammatory Markers

When to Use CRP vs. ESR

• CRP is preferred for:

  • Acute inflammatory conditions and infections
  • Initial diagnosis of inflammatory conditions
  • Monitoring response to therapy
  • Cardiovascular risk assessment 1

• ESR is preferred for:

  • Chronic inflammatory conditions
  • Monitoring certain autoimmune diseases (e.g., systemic lupus erythematosus)
  • Detecting low-grade bone infections 4
  • When CRP is normal but inflammation is still suspected 2

Interpretation of Combined CRP and ESR Results

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 [2]

CRP/ESR Discordance

Discordance between CRP and ESR occurs in approximately 12% of patients 5:

• High CRP/Low ESR pattern is associated with:

  • Acute infections (urinary tract, gastrointestinal, pulmonary, bloodstream)
  • Myocardial infarction
  • Venous thromboembolism 5

• High ESR/Low CRP pattern is associated with:

  • Connective tissue diseases (e.g., systemic lupus erythematosus)
  • Ischemic stroke or transient ischemic attack
  • Bone and joint infections 5

Proper Testing Methodology

For optimal CRP assessment:

• Obtain samples when patient is metabolically stable
• Avoid testing during obvious infection or inflammation
• Express results in mg/L only
• Consider two measurements (optimally 2 weeks apart) for stable estimate
• If level is >10 mg/L, search for source of infection/inflammation and repeat test 1

Additional Inflammatory Markers in Specific Contexts

For Rheumatologic Evaluation

• Rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA) for rheumatoid arthritis 1
• Antinuclear antibodies (ANA) for systemic lupus erythematosus and other autoimmune diseases 2

For Gastrointestinal Inflammation

• Fecal calprotectin for intestinal inflammation 1

For Neurological Inflammation

• Cerebrospinal fluid analysis for central nervous system inflammation 1

Limitations and Pitfalls

• Neither CRP nor ESR is specific for any particular disease
• Both can be elevated in non-inflammatory conditions (obesity can elevate CRP) 2
• Don't treat the marker itself; treat the underlying cause 2
• Always interpret inflammatory markers in clinical context 2
• Don't dismiss elevated ESR when CRP is normal, as this pattern can occur in serious conditions 2
• Avoid assuming low CRP rules out bacterial infection 2

By understanding the characteristics and appropriate use of inflammatory markers, clinicians can more effectively diagnose and monitor inflammatory conditions while avoiding common interpretive errors.