Which plasma protein is the least abundant under normal conditions?

• A. Albumin
• B. Immunoglobulins
• C. Fibrinogen
• D. Transferrin

Answer: (C)

Plasma protein levels vary widely, with albumin forming the largest share to maintain oncotic pressure and serve as a carrier for various substances. Immunoglobulins are also abundant because they are continuously produced by plasma cells to provide immune defense, and transferrin is present in moderate amounts to transport iron. Fibrinogen, while essential for clot formation, circulates at a much lower steady-state concentration in healthy individuals. It’s kept at a relatively low baseline so there isn’t a predisposition to spontaneous coagulation, and during coagulation it rapidly converts to fibrin when needed. Because of its comparatively small resting level, fibrinogen is the least abundant among these normal plasma proteins.