C-reactive protein (CRP) is synthesized in the liver. It begins to rise within 4–6 hours after stimulus from an inflammation or infection. The level doubles every eight hours and peaks at 36–50 hours.
CRP is a sensitive marker of inflammation and tissue damage. However, it has a low specificity. Conditions other than sepsis that can cause a rise in CRP levels include:
- Rheumatic diseases
- Systemic lupus erythematosus
- Systemic sclerosis
- Sjogren syndrome
- Inflammatory bowel disease
- Leukemia
- Transfusion-associated graft-vs-host disease
Once sepsis is determined and therapy initiated, CRP is useful for monitoring response to antibiotics and predicting prognosis.
CRP levels of <3 mcg/mL are considered within the normal range, while levels >150 mcg/mL are considered positive for sepsis in a patient suspected of having sepsis.
