CRP
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CRP Key Points
- Acute phase protein that is synthesised in the liver.
- Protein C is not related to CRP.
- CRP binds to phosphocoline on dead or dying cells and some bacteria activating the compliment system.
- CRP rises are seen in inflammatory, infectious, malignant conditions and trauma.
- CRP may also rise in obesity and pregnancy
- Its half life is approximately 18 hours
Background
CRP is an acute-phase protein, part of the innate immune system. It belongs to the pentraxin family of proteins and is named for its ability to bind the C-polysaccharide of Streptococcus pneumoniae.
Production
- CRP is synthesised mainly by the liver.
- Production is stimulated by IL-6 (also IL-1β, TNF-α).
Functions
- Pattern recognition molecule: binds to phosphocholine on dead/dying cells and pathogens.
- Opsonisation: promotes phagocytosis by macrophages and neutrophils.
- Complement activation: via the classical pathway (binds C1q).
- Modulates inflammation: interacts with Fcγ receptors on immune cells.
Characteristics
- Non-specific marker of inflammation and tissue injury.
- Rises within 6–8 hours of an inflammatory stimulus.
- Peaks at 48 hours, half-life ~18 hours.
- Falls quickly once inflammation resolves (useful for monitoring).
Normal levels & clinical use
In most UK trusts normal: <5 mg/L
CRP may be used to:
- Monitor treatment response (e.g., sepsis, pneumonia, autoimmune flare).
- Some would argue CRP has a use in helping to differentiate bacterial vs viral infections (Bacteria trigger strong IL-6, TNF-α, and IL-1β release from innate immune cells & are associated with more marked rise in CRP than viral infections).
- Predict cardiovascular risk when measured as hs-CRP (high sensitivity CRP).