Acute phase response: CRP, ESR, ferritin and procalcitonin
How IL-6 drives the hepatic acute phase response, the kinetics and confounders of CRP, ESR, ferritin and procalcitonin, why they disagree in SLE, myeloma and on tocilizumab, and how to use them to monitor disease and guide antibiotics.
Tier 1Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- The acute phase response is the liver's change in protein production during inflammation, driven mainly by IL-6, with IL-1 and TNF.
- Positive acute phase proteins rise: CRP, serum amyloid A, fibrinogen, ferritin, haptoglobin, hepcidin, complement C3 and C4, alpha-1 antitrypsin, caeruloplasmin.
- Negative acute phase proteins fall: albumin, transferrin, transthyretin (prealbumin).
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Sources
- American Society of Hematology 2026 guidelines for diagnosis of iron deficiencyPowers JM et al., Blood Adv 2026, 2026
- RCPA Manual: C-reactive protein, erythrocyte sedimentation rate, procalcitonin, ferritinAU/NZRoyal College of Pathologists of Australasia, 2025
- Gabay C, Kushner I. Acute-phase proteins and other systemic responses to inflammation. N Engl J Med 1999;340:448-54New England Journal of Medicine, 1999
- Dark P et al. Biomarker-guided antibiotic duration for hospitalized patients with suspected sepsis: the ADAPT-Sepsis randomized clinical trial. JAMA 2025;333:682-93JAMA, 2025
- Evans L et al. Surviving Sepsis Campaign: international guidelines for management of sepsis and septic shock 2021. Crit Care Med 2021;49:e1063-143Society of Critical Care Medicine / European Society of Intensive Care Medicine, 2021
- Miller A, Green M, Robinson D. Simple rule for calculating normal erythrocyte sedimentation rate. BMJ 1983;286:266BMJ, 1983
- Bruns AH et al. Usefulness of consecutive C-reactive protein measurements in follow-up of severe community-acquired pneumonia. Eur Respir J 2008;32:726-32European Respiratory Journal, 2008
- Robbins and Cotran Pathologic Basis of Disease (10th ed.)Elsevier (Kumar, Abbas and Aster, 2020), 2020
- Last updated
- 14 November 2026
What changed
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