Which equation correctly defines total iron-binding capacity (TIBC)?

Which equation correctly defines total iron-binding capacity (TIBC)?

• A. TIBC = UIBC + Serum iron
• B. TIBC = Serum iron - UIBC
• C. TIBC = Serum iron × UIBC
• D. TIBC = UIBC / Serum iron

Answer: (A)

TIBC measures the total capacity of transferrin in the blood to bind iron. Some iron is already bound to transferrin (serum iron), and the remaining unoccupied binding sites represent the unsaturated iron-binding capacity (UIBC). By definition, the total binding capacity is the sum of the iron already bound and the iron that can still be bound. So TIBC = UIBC + serum iron. Subtracting, multiplying, or dividing would not reflect the idea of total binding capacity, which is inherently additive.

TIBC measures the total capacity of transferrin in the blood to bind iron. Some iron is already bound to transferrin (serum iron), and the remaining unoccupied binding sites represent the unsaturated iron-binding capacity (UIBC). By definition, the total binding capacity is the sum of the iron already bound and the iron that can still be bound. So TIBC = UIBC + serum iron. Subtracting, multiplying, or dividing would not reflect the idea of total binding capacity, which is inherently additive.