Which is the correct formula to calculate transferrin saturation?

Which is the correct formula to calculate transferrin saturation?

• A. Serum iron / UIBC × 100
• B. Serum iron / TIBC × 100
• C. TIBC / Serum iron × 100
• D. (UIBC + Serum iron) / Serum iron × 100

Answer: (B)

Transferrin saturation shows what portion of transferrin’s iron-binding sites are filled. Transferrin has binding sites for iron, and TIBC represents the total capacity to bind iron. The fraction of sites occupied by iron is given by serum iron divided by TIBC, then expressed as a percentage. Therefore, transferrin saturation = (serum iron / TIBC) × 100. Since TIBC is roughly equal to serum iron plus UIBC, this can also be thought of as serum iron /(serum iron + UIBC) × 100. For example, if serum iron is 100 μg/dL and TIBC is 300 μg/dL, transferrin saturation would be 33%. Other formulas don’t measure the occupied binding sites. Using serum iron with UIBC, or inverting the ratio with TIBC/serum iron, or (UIBC + serum iron) divided by serum iron all misrepresent the concept of saturation.

Transferrin saturation shows what portion of transferrin’s iron-binding sites are filled. Transferrin has binding sites for iron, and TIBC represents the total capacity to bind iron. The fraction of sites occupied by iron is given by serum iron divided by TIBC, then expressed as a percentage.

Therefore, transferrin saturation = (serum iron / TIBC) × 100. Since TIBC is roughly equal to serum iron plus UIBC, this can also be thought of as serum iron /(serum iron + UIBC) × 100.

For example, if serum iron is 100 μg/dL and TIBC is 300 μg/dL, transferrin saturation would be 33%.

Other formulas don’t measure the occupied binding sites. Using serum iron with UIBC, or inverting the ratio with TIBC/serum iron, or (UIBC + serum iron) divided by serum iron all misrepresent the concept of saturation.