Which protein is an acute-phase reactant?

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

Answer: (A)

Inflammation triggers the liver to produce acute-phase proteins, with some increasing (positive acute-phase reactants) and others decreasing (negative acute-phase). C-reactive protein is the classic positive acute-phase protein that rises rapidly in response to inflammatory cytokines like IL-6, often within hours and peaking within a day or two. This rapid, marked increase makes CRP a reliable indicator of acute inflammation or infection. In contrast, albumin and transferrin are negative acute-phase reactants; their levels fall during inflammation because the liver shifts its production toward positive reagents. Hemopexin is not typically used as a primary acute-phase marker in routine testing. Therefore, the protein that best fits as an acute-phase reactant here is C-reactive protein.