Which of the following is a positive acute-phase reactant?

• A. Albumin
• B. Transferrin
• C. CRP
• D. Antithrombin

Answer: (C)

Positive acute-phase reactants are proteins produced by the liver whose levels rise during inflammation. C-reactive protein is a classic example: its production is upregulated by inflammatory cytokines (like IL-6), causing rapid increases in the blood within hours and peaking within a day or two, then falling as the inflammation resolves. This makes CRP a sensitive marker for inflammation and infection. Albumin and transferrin behave oppositely—they decrease during the acute-phase response, so they are negative acute-phase reactants. Antithrombin isn’t considered a classic acute-phase reactant; its levels can change in illness due to factors like consumption or loss, but it’s primarily a coagulation inhibitor rather than a marker of the acute-phase response. Hence, CRP is the positive acute-phase reactant.