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Acute Phase reactants
Related Subjects: |Ferritin |CEA |ESR |CRP |ALP |LDH |HbA1c |Alpha Fetoprotein |Anti-Hu ab |Biochemical Lab values
๐ก๏ธ 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-ฮฑ, 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.
๐ Summary of Acute Phase Reactants
| Acute Phase Reactant | Main Role | Clinical Notes |
|---|---|---|
| ๐งช C-reactive protein (CRP) | Produced by liver in response to IL-6. Marker of inflammation & tissue injury. | Rises rapidly (within 6โ8h); useful for infection monitoring. Faster than ESR. |
| ๐ฉธ Fibrinogen | Clotting factor โ converted to fibrin. | Elevated fibrinogen prolongs ESR; risk marker for CV disease. |
| ๐ Serum amyloid A (SAA) | Acute inflammation protein, lipid transport, immune modulation. | Massive rise in acute infection; prolonged elevation โ amyloidosis. |
| ๐งฒ Ferritin | Iron storage protein; sequesters iron from pathogens. | Also rises in HLH, COVID, Stillโs disease (hyperferritinaemia). |
| ๐ก๏ธ Haptoglobin | Binds free Hb โ prevents oxidative damage. | โ in inflammation; โ in haemolysis (consumed). |
| ๐งฌ Alpha-1 antitrypsin | Protease inhibitor โ protects tissues from neutrophil elastase. | Deficiency โ emphysema & liver disease; rises with inflammation. |
| โก Ceruloplasmin | Copper-binding protein, antioxidant & iron metabolism. | Rises with inflammation; โ in Wilsonโs disease. |
| โฌ๏ธ Negative Acute Phase Reactants (fall during inflammation) | ||
| ๐ง Albumin | Maintains oncotic pressure; carrier protein. | Falls in inflammation, sepsis, malnutrition; prognostic marker. |
| ๐ Transferrin | Iron transport protein. | Falls during inflammation โ helps restrict iron to pathogens. |
| ๐ Transthyretin (Prealbumin) | Transports thyroxine & retinol-binding protein. | Falls in acute inflammation and malnutrition; short half-life โ good nutritional marker. |
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