Inflammation Blood Tests: Beyond CRP
CRP is the most ordered inflammation marker — but it only tells part of the story. ESR, ferritin, fibrinogen, IL-6, homocysteine, and the neutrophil:lymphocyte ratio each capture different aspects of the inflammatory process. Here is when each one adds clinical value.
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Inflammation markers differ in specificity (what they respond to), sensitivity (how quickly they rise), and half-life (how quickly they normalise). Understanding these differences helps choose the right test for the clinical question — whether that is diagnosing acute infection, monitoring chronic autoimmune disease, tracking cardiovascular risk, or identifying occult malignancy.
Inflammation Markers — The Full Panel
| Test | Half-Life / Speed | Best Used For | Normal Range |
|---|---|---|---|
| CRP (standard) | 19 hours; rises within 4–6 hours | Acute infection, surgery response monitoring, general inflammation screen | Below 5–10 mg/L |
| hs-CRP | Same as CRP but more sensitive assay | Cardiovascular risk stratification at low inflammation levels; below 3 mg/L where standard CRP cannot detect | Below 1 mg/L (optimal below 0.5) |
| ESR (erythrocyte sedimentation rate) | Days; slow to rise and fall | Chronic inflammatory conditions, temporal arteritis (ESR typically above 50), monitoring disease activity over weeks to months | Below 15 mm/hr (men under 50); below 20 (women under 50); higher with age |
| Ferritin (as acute phase protein) | Rises with any acute inflammation | Haemophagocytic lymphohistiocytosis (ferritin above 10,000 is a diagnostic criterion); extreme ferritin elevation suggests serious inflammatory or malignant condition | 12–150 ng/mL (note: also a nutrient marker — context-dependent) |
| Fibrinogen | Rises within 24 hours; peaks at 72 hours | Clotting system activation; cardiovascular risk; DIC monitoring; also acute phase reactant | 200–400 mg/dL |
| IL-6 | Peaks at 2–4 hours; very short half-life | Earliest acute infection/sepsis marker; cytokine storm monitoring (used in COVID-19); research settings | Below 7 pg/mL |
| Neutrophil:lymphocyte ratio (NLR) | Immediate (calculated from CBC differential) | Systemic inflammation, sepsis severity, cancer prognosis, surgical outcome prediction | Below 2.5 (above 5 suggests significant systemic stress) |
CRP vs ESR: Which to Order When
CRP is a better acute infection marker — it rises and falls faster, and its concentration correlates better with bacterial infection severity than ESR. ESR is a better chronic disease monitoring marker — it reflects changes over weeks, making it useful for tracking polymyalgia rheumatica, rheumatoid arthritis, and multiple myeloma response to treatment. When both are elevated and discordant (e.g. very high ESR with normal CRP), consider paraproteinaemia (plasma cell disorders) — elevated immunoglobulins increase plasma viscosity and raise ESR without raising CRP.
CRP Pattern Helps Identify Cause
CRP below 0.3 mg/L: no significant inflammation. CRP 0.3–1.0: low-level chronic inflammation (metabolic syndrome, early atherosclerosis, sleep apnoea). CRP 1.0–10.0: significant inflammation — investigate for autoimmune disease, infection, or severe metabolic dysfunction. CRP above 10: likely active infection or acute inflammatory disease. CRP above 100: serious bacterial infection or major tissue injury — seek urgent evaluation.
The Cardiovascular Case for hs-CRP
Standard CRP cannot distinguish between 0.3 mg/L and 2.5 mg/L — both below the 5 mg/L upper limit of normal. Yet the cardiovascular risk difference between hs-CRP below 1 mg/L and hs-CRP of 3 mg/L is substantial: the latter nearly doubles the risk of major adverse cardiovascular events. hs-CRP belongs on every cardiovascular risk assessment, particularly in patients whose LDL appears "normal" but who have other risk factors. It is also the test most likely to direct the physician toward anti-inflammatory interventions (omega-3 fatty acids, exercise, dietary quality) as part of cardiovascular risk reduction.
Medical Disclaimer
This article is for educational purposes only and does not constitute medical advice. Reference ranges, supplement dosages, and nutritional information mentioned are general educational guidance from published research—not personalised recommendations. Do not use this content to self-diagnose or self-treat any condition. Always consult a qualified healthcare provider before making any changes to your health regimen, medications, or supplements.
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