C-Reactive Protein
An acute-phase protein produced by the liver in response to inflammation. CRP levels rise rapidly during infection, tissue injury, or systemic inflammatory disease, making it a sensitive but non-specific marker of inflammation in dogs.
C-reactive protein (CRP) is an acute-phase protein synthesized by the liver in response to pro-inflammatory cytokines, particularly interleukin-6 (IL-6). In dogs, CRP is one of the most sensitive acute-phase reactants — levels can increase 10- to 100-fold within 24 hours of an inflammatory stimulus, making it a rapid indicator of systemic inflammation.
What CRP Measures
CRP does not identify the cause of inflammation — it quantifies its magnitude. It rises in response to:
- Bacterial, viral, and fungal infections
- Tissue injury (surgery, trauma)
- Autoimmune and immune-mediated diseases (IMHA, IMPA)
- Pancreatitis and other acute abdominal conditions
- Neoplasia (cancer), particularly with tissue necrosis
- Inflammatory bowel disease
The non-specific nature is both a strength (sensitive screening) and a limitation (requires additional testing to identify the underlying cause).
Clinical Applications
Monitoring Treatment Response
CRP’s rapid kinetics make it ideal for tracking treatment effectiveness. A dog with bacterial pneumonia starting antibiotics should show declining CRP within 24-48 hours if the treatment is effective. Persistently elevated or rising CRP despite treatment suggests inadequate therapy, resistant organisms, or an additional disease process.
Post-Surgical Monitoring
CRP normally rises after surgery (tissue trauma) and should decline over 3-5 days during uncomplicated recovery. Failure to decline or secondary elevation suggests post-operative complications (infection, dehiscence, implant reaction).
Chronic Inflammation and Aging
Emerging research connects persistently mildly elevated CRP with accelerated aging — the concept of “inflammaging.” Chronic low-grade inflammation, measurable through CRP, drives progressive tissue damage and contributes to arthritis, cognitive decline, and cardiovascular disease.
Reference Values
| Category | CRP (mg/L) | Interpretation |
|---|---|---|
| Normal | <10 | No significant inflammation |
| Mild elevation | 10-40 | Low-grade or resolving inflammation |
| Moderate elevation | 40-100 | Active inflammatory process |
| Marked elevation | >100 | Severe inflammation, infection, or necrosis |
Limitations
CRP does not replace diagnostic imaging, culture, or biopsy — it indicates that something is wrong, not what. Corticosteroid therapy suppresses CRP production, potentially masking ongoing inflammation. CRP is species-specific: canine CRP assays are required (human assays do not work).