Lab Interpretation Guide
Inflammation Markers Blood Test
CRP · ESR · Procalcitonin · Fibrinogen · IL-6 · WBC — Full Reference
Key Principle
No single inflammation marker is diagnostic on its own. The combination of CRP, WBC, procalcitonin, ESR, and clinical context together determines the nature and severity of the inflammatory process — bacterial vs. viral vs. autoimmune vs. sterile.
Inflammation Markers Explained
CRP (C-Reactive Protein)
Rises in 6–12h
Normal: < 5 mg/L
General acute inflammation marker. Rises with bacterial infection, autoimmune flare, tissue damage, and post-surgery. Sensitive but non-specific.
5–20 mild · 20–80 significant · > 80 severe / sepsis risk
ESR (Erythrocyte Sedimentation Rate)
Rises over 24–48h
Normal: < 15 mm/h (men) · < 20 mm/h (women)
Less specific than CRP. Elevated in chronic inflammation, autoimmune disease, infections, anemia, and malignancy. Useful for disease monitoring.
> 40 elevated · > 80 significant · > 100 serious pathology
Procalcitonin (PCT)
Rises in 2–4h (bacterial)
Normal: < 0.25 ng/mL
Most specific marker for bacterial infection. Stays low in viral infections. Key tool for sepsis diagnosis and antibiotic stewardship decisions.
0.25–0.5 borderline · 0.5–2 possible · 2–10 probable sepsis · > 10 severe sepsis
Fibrinogen
Rises in 24–72h
Normal: 1.8–3.5 g/L
Acute-phase reactant and coagulation factor. Elevated in systemic inflammation. Low in DIC or liver failure. Also an independent cardiovascular risk marker.
> 4.0 prothrombotic · > 5.0 coagulopathy or severe inflammation
WBC (White Blood Count)
Changes within hours
Normal: 4.0–10.0 × 10⁹/L
Leukocytosis (> 12) suggests bacterial infection or stress response. Leukopenia (< 4) may indicate viral infection, bone marrow suppression, or sepsis.
> 12 leukocytosis · > 20 severe infection / leukemia · < 4 leukopenia
Pattern Recognition
CRP ↑↑ + WBC ↑ + PCT ↑
Bacterial infection — source identification and cultures indicated
CRP ↑ + WBC normal + PCT normal
Viral infection or non-infectious inflammation likely
CRP ↑ + ESR ↑↑ + WBC normal
Chronic or autoimmune inflammation — consider ANA, RF, anti-dsDNA
PCT > 2 + CRP > 80 + Lactate > 2
Sepsis pattern — urgent clinical evaluation required immediately
Fibrinogen ↑↑ + D-Dimer ↑ + PLT ↑
Prothrombotic inflammatory state — thrombosis risk elevated, not DIC
CRP normal + ESR ↑ + anemia
Chronic disease pattern — myeloma, malignancy, or inflammatory disease
Key Clinical Points
- •Always interpret inflammation markers as a panel — no single value is diagnostic
- •CRP and PCT together reliably distinguish bacterial from viral infection in most clinical scenarios
- •ESR > 100 mm/h in an elderly patient: rule out giant cell arteritis, myeloma, and malignancy
- •Procalcitonin < 0.1 ng/mL makes serious bacterial infection or sepsis very unlikely
- •Fibrinogen > 5 g/L with elevated D-Dimer suggests DIC or severe systemic inflammation
- •IL-6 rises before CRP — useful in very early infection but less widely available
- •Steroid therapy suppresses CRP and WBC — may mask infection in immunosuppressed patients
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