C-reactive protein (CRP) is an acute-phase protein produced by the liver in response to inflammation, infection, or tissue injury.
Mechanism: Triggered by IL-6 signaling. Rises within hours of acute inflammation, can stay chronically elevated under low-grade systemic inflammation (metabolic disease, autoimmunity, chronic stress).
Lab range: High-sensitivity CRP (hs-CRP) is the right test for cardiovascular risk. Less than 1.0 mg/L = low risk; 1-3 = average; greater than 3 = elevated. Acute illness can spike it to 100+; ignore for trending until baseline returns.
Caveats: Non-specific (doesn't tell you the source). Pair with ferritin, ESR, and clinical context. Don't draw CRP within 2 weeks of any infection or vaccination.