Which formula provides the best estimate of serum TIBC?

The formula that provides the best estimate of serum total iron-binding capacity (TIBC) is derived from the relationship between serum transferrin levels and TIBC. Transferrin is the primary protein in the blood that binds to iron and transports it throughout the body. The conversion factor used in the correct answer, which is multiplying serum transferrin (measured in mg/dL) by 1.43, accurately reflects the fact that one mg/dL of transferrin can bind approximately 1.43 µg/dL of iron.

This relationship is grounded in the biochemistry of iron transport: transferrin binds iron in a 1:1 stoichiometry, and the factor accounts for the molecular weight differences between the units of measurement. Therefore, this calculation allows for an accurate estimation of how much iron can be bound by transferrin in the serum, thereby providing a reliable estimate for TIBC.

The other choices either use incorrect conversion factors or formulas that do not directly correspond to the established biochemical relationships involved in iron transport and transferrin's role. Utilizing the correct relationship ensures that laboratory results for TIBC are both clinically relevant and reflective of the body's capacity to transport iron.