Measurement of CRP levels can be used for all of the following except which?

• A. Diagnosing a specific bacterial infection
• B. Monitoring drug therapy with anti-inflammatory agents
• C. Tracking the progress of an organ transplant
• D. Determining active phases of rheumatoid arthritis

Answer: (A)

C-reactive protein is an acute-phase protein produced by the liver in response to inflammation. Its level rises in many inflammatory states, making it a general marker of inflammatory activity rather than a test that identifies a specific pathogen. This nonspecific nature is why CRP is useful for tracking how well anti-inflammatory therapy is working: as inflammation decreases, CRP tends to fall. It can also help monitor status after organ transplantation, since graft inflammation or rejection can raise CRP levels and trends over time provide useful information. Similarly, in rheumatoid arthritis, CRP levels reflect the activity of the disease—the higher the inflammation, the higher the CRP, and it often decreases as the disease comes under control. However, CRP cannot diagnose a specific bacterial infection because it does not reveal which organism is causing the illness; other tests are needed to identify the pathogen.