C-reactive protein (CRP) is synthesized in the liver. It begins to rise within 4–6 hours after a 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 µg/mL are considered within the normal range, while levels >150 µg/mL are considered positive for sepsis in a patient suspected of having sepsis.
