A C-reactive protein (CRP) blood test measures the level of CRP, a substance produced by the liver in response to inflammation. Elevated CRP levels indicate inflammation in the body, which can be caused by infections, chronic diseases like arthritis, or cardiovascular conditions. While normal CRP levels are generally below 3 milligrams per liter (mg/L), higher levels may signal acute inflammation or an increased risk of heart disease. CRP tests are used to assess the severity of inflammation and guide diagnosis and treatment plans, making them crucial for monitoring overall health.