What labs should be ordered to check for inflammation?

Laboratory Tests to Check for Inflammation

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

Primary Inflammatory Marker

High-Sensitivity C-reactive Protein (hs-CRP)

• hs-CRP is the analyte of choice among all inflammatory markers based on analyte stability, assay precision, accuracy, commercial availability, and standardization capabilities 1
• Obtain two measurements, either fasting or nonfasting, optimally 2 weeks apart, and average the results to reduce within-individual variability 1
• Perform testing only in metabolically stable patients without obvious inflammatory or infectious conditions 1
• Report results only as mg/L, expressed to 1 decimal point 1

Interpretation of hs-CRP Results

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

Additional Laboratory Tests Based on Clinical Context

For Intestinal Inflammation (Crohn's Disease, Colitis)

• CRP should be assessed as a marker of inflammation, though patients may have normal CRP levels despite active disease 1
• Fecal calprotectin (preferred) or lactoferrin can assess intestinal inflammation and differentiate from irritable bowel syndrome 1
• Complete blood count to assess for anemia from chronic blood loss 1
• Albumin to evaluate nutritional status and disease severity 1
• Liver profile, iron studies, renal function, and vitamin B12 as routine monitoring 1

General Inflammatory Assessment

• Complete blood count (CBC) provides white blood cell count, though it lacks specificity for distinguishing bacterial versus viral infections 1
• Erythrocyte sedimentation rate (ESR) is a traditional marker but lacks sufficient specificity to appraise disease activity in many conditions 2

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
• Do not use hs-CRP for monitoring therapy response, as the role of inflammatory markers in treatment monitoring has not been established 1
• Do not rely on a single hs-CRP measurement due to within-individual variability 1
• 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
• Do not use CBC-derived ratios (neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio) as primary inflammatory markers, as they are not completely specific or sensitive despite some prognostic value in specific rheumatic conditions 2

Context-Specific Considerations

The CDC/AHA guidelines emphasize that hs-CRP measurement should not replace traditional risk factor assessment but can be used as an optional measurement to adjust risk estimates 1. The high-risk tertile (>3.0 mg/L) demonstrates a 2-fold increase in relative risk compared to the low-risk tertile, based on distributions from 15 populations involving 40,000 persons 1.

For gastrointestinal inflammation specifically, stool inflammatory markers (calprotectin or lactoferrin) have higher sensitivity and specificity than serum markers for detecting intestinal inflammation 1, making them preferable when intestinal pathology is suspected.