What labs should be ordered to evaluate inflammation in the body?

Laboratory Tests to Order for Inflammation in the Body

Order high-sensitivity C-reactive protein (hs-CRP) as the primary and preferred inflammatory marker, measured twice (optimally 2 weeks apart) and averaged, as it has superior analytic characteristics compared to all other inflammatory markers. 1, 2

Primary Inflammatory Marker: hs-CRP

hs-CRP is the single best laboratory test for assessing systemic inflammation based on analyte stability, assay precision, commercial availability, and standardization capabilities. 1, 2

Measurement Protocol

• Obtain two measurements, either fasting or nonfasting, optimally 2 weeks apart, and average the results to reduce within-individual variability. 1, 2
• Perform testing only in metabolically stable patients without obvious inflammatory or infectious conditions. 2
• Report results only as mg/L, expressed to 1 decimal point. 1, 2

Interpretation Framework

• Low risk: hs-CRP <1.0 mg/L 1, 2
• Average risk: hs-CRP 1.0 to 3.0 mg/L 1, 2
• High risk: hs-CRP >3.0 mg/L (demonstrates 2-fold increase in relative risk) 1, 2
• If hs-CRP ≥10 mg/L: Search for obvious sources of infection or inflammation, discard that result, and repeat testing in 2 weeks. 1, 2, 3

Additional Laboratory Tests Based on Clinical Context

Complete Blood Count (CBC)

• Order CBC to assess white blood cell count, though it lacks specificity for distinguishing bacterial versus viral infections. 2
• WBC and platelet dynamics can help define inflammatory recovery patterns. 4
• Check for leukocytosis, left-shift, or neutropenia when infection is suspected. 3

Context-Specific Testing

For Intestinal Inflammation (Crohn's Disease, Ulcerative Colitis):

• Fecal calprotectin (preferred) or lactoferrin to assess intestinal inflammation and differentiate from irritable bowel syndrome—these have higher sensitivity and specificity than serum markers for detecting intestinal inflammation. 2
• CRP should be assessed, though patients may have normal CRP levels despite active disease (31.4% false-negative rate). 2, 3
• Albumin to evaluate nutritional status and disease severity. 2
• Liver profile, iron studies, renal function, and vitamin B12 as routine monitoring. 2

For Suspected Infection:

• Blood cultures if fever, tachycardia, or hemodynamic compromise is present. 3
• Procalcitonin if available to help differentiate bacterial infection. 3
• Liver function tests (AST/ALT) to exclude hepatic inflammation. 3

Erythrocyte Sedimentation Rate (ESR)

• ESR can be used as a complementary marker, particularly in rheumatic diseases. 5
• ESR >40-50 mm/h warrants urgent evaluation for conditions like giant cell arteritis. 3, 6
• CRP normalizes more quickly than ESR during resolution of inflammation. 3

Critical Pitfalls to Avoid

• Do not order alternative inflammatory markers (serum amyloid A, soluble adhesion molecules, cytokines) as they lack standardization, commercial availability, or require frozen samples limiting clinical use. 1, 2
• Do not rely on a single hs-CRP measurement due to within-individual variability. 1, 2
• Do not interpret elevated inflammatory markers in isolation—other acute inflammatory conditions (inflammatory bowel disease, rheumatoid arthritis, chronic alcoholism) can cause mildly to moderately increased levels. 1, 2
• Approximately 20% of smokers have CRP >10 mg/L from smoking alone, and obesity, age, sex, and race significantly affect baseline CRP levels. 3
• A single normal CRP does not rule out infection. 3
• Do not use hs-CRP for monitoring therapy response, as the role of inflammatory markers in treatment monitoring has not been established. 2

Clinical Context for CRP Levels

The magnitude of CRP elevation provides diagnostic clues: 3

• Acute bacterial infections: median ~120 mg/L
• Inflammatory diseases: median ~65 mg/L
• Solid tumors: median ~46 mg/L
• Non-bacterial infections: median ~32 mg/L
• Stable cardiovascular disease: median ~6 mg/L