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Acute Phase reactants
Related Subjects: |Ferritin |CEA |ESR |CRP |ALP |LDH |HbA1c |Alpha Fetoprotein |Anti-Hu ab |Biochemical Lab values
🌡️ Introduction
- Acute phase reactants (APRs) are proteins whose plasma concentrations change in response to inflammation, infection, trauma, or stress. They are part of the innate immune response and help mediate & modulate inflammation.
- The response is driven by cytokines such as IL-1, IL-6, and TNF-α, released by immune cells after tissue injury or infection.
- Measuring APRs is clinically important for diagnosing and monitoring conditions like infections, autoimmune diseases, and cancers.
- Positive APRs (e.g. CRP, fibrinogen, ferritin) rise with inflammation. Negative APRs (e.g. albumin, transferrin) fall, reflecting diversion of resources and disease severity.
📊 Summary of Acute Phase Reactants
| Acute Phase Reactant | Main Role | Clinical Notes |
|---|---|---|
| 🧪 C-reactive protein (CRP) | Produced by liver in response to IL-6. Marker of inflammation & tissue injury. | Rises rapidly (within 6–8h); useful for infection monitoring. Faster than ESR. |
| 🩸 Fibrinogen | Clotting factor → converted to fibrin. | Elevated fibrinogen prolongs ESR; risk marker for CV disease. |
| 📈 Serum amyloid A (SAA) | Acute inflammation protein, lipid transport, immune modulation. | Massive rise in acute infection; prolonged elevation → amyloidosis. |
| 🧲 Ferritin | Iron storage protein; sequesters iron from pathogens. | Also rises in HLH, COVID, Still’s disease (hyperferritinaemia). |
| 🛡️ Haptoglobin | Binds free Hb → prevents oxidative damage. | ↑ in inflammation; ↓ in haemolysis (consumed). |
| 🧬 Alpha-1 antitrypsin | Protease inhibitor → protects tissues from neutrophil elastase. | Deficiency → emphysema & liver disease; rises with inflammation. |
| ⚡ Ceruloplasmin | Copper-binding protein, antioxidant & iron metabolism. | Rises with inflammation; ↓ in Wilson’s disease. |
| ⬇️ Negative Acute Phase Reactants (fall during inflammation) | ||
| 💧 Albumin | Maintains oncotic pressure; carrier protein. | Falls in inflammation, sepsis, malnutrition; prognostic marker. |
| 🔗 Transferrin | Iron transport protein. | Falls during inflammation → helps restrict iron to pathogens. |
| 🔄 Transthyretin (Prealbumin) | Transports thyroxine & retinol-binding protein. | Falls in acute inflammation and malnutrition; short half-life → good nutritional marker. |
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