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Iron-binding capacity and transferrin saturation

13 min

Skills you'll build

  • Calculate TIBC from transferrin using the procedure's factor and units
  • Calculate TIBC or UIBC from the other iron-capacity measurements
  • Calculate transferrin saturation from serum iron and TIBC

Read the full reference

Try first

Try first

One serum specimen has an iron of 90 µg/dL and a total iron-binding capacity (TIBC) of 360 µg/dL. What is the transferrin saturation?

Keep going to build the reasoning.

Right. Keep going to follow the reasoning.

Keep going to build the reasoning.

Keep going to build the reasoning.

Get the idea

Use the explanation to check your first decision.

Iron in serum travels bound to transferrin. The iron studies describe that transport in three linked numbers:

  • how much iron is bound
  • how much more the transferrin could bind
  • what share of the total is already occupied

Total and unsaturated capacity

Total iron-binding capacity (TIBC) is the iron already bound plus the unsaturated iron-binding capacity (UIBC) still free:

TIBC = serum iron + UIBC

UIBC = TIBC − serum iron

Some procedures measure iron and UIBC and calculate TIBC by adding them.2

Saturation

Transferrin saturation is the occupied share of the capacity, so the iron goes on top:

transferrin saturation (%) = serum iron ÷ TIBC × 100

An iron of 60 µg/dL with a TIBC of 300 µg/dL gives 60 ÷ 300 × 100 = 20%. Every number in these formulas must come from the same specimen and be in the same units, µg/dL in US reports.1

TIBC from transferrin

Some procedures measure transferrin and calculate TIBC from it with a factor the procedure states:

TIBC (µg/dL) = transferrin (mg/dL) × procedure factor

  • The factor belongs to the procedure. One reference laboratory's procedure uses 1.18. The theoretical binding of iron by transferrin gives about 1.4.1,2 Use only the factor your validated procedure names.
  • The factor is stated per mg/dL of transferrin, so a result reported in g/L is converted first. Multiply by 100, which turns 2.50 g/L into 250 mg/dL. Applying the factor to the g/L number gives a TIBC 100 times too small.

Check the answer

TIBC includes the bound iron. A TIBC below the serum iron, or a saturation above 100%, sends you back to the inputs, their units and the specimen before anything is reported.

For comparison, one reference laboratory lists these adult serum reference intervals:1

TestAdult reference interval
Iron, men50 to 150 µg/dL
Iron, women35 to 145 µg/dL
TIBC250 to 400 µg/dL
Transferrin saturation14% to 50%

Intervals differ between laboratories and methods, so each report carries its own.

Follow the bench demonstration

Sources for this step
References
  1. Mayo Clinic Laboratories. Iron and Total Iron-Binding Capacity, Serum. Accessed September 7, 2026.
  2. Yamanishi H, Iyama S, Yamaguchi Y, Kanakura Y, Iwatani Y. Total iron-binding capacity calculated from serum transferrin concentration or serum iron concentration and unsaturated iron-binding capacity. Clin Chem. 2003;49(1):175-178. doi:10.1373/49.1.175

Watch one

Follow each move and the reason beside it.

An adult woman's serum specimen has an iron of 40 µg/dL and a UIBC of 380 µg/dL, both measured on the same specimen. Calculate the TIBC and the transferrin saturation, and compare them with the example adult reference intervals:

  • TIBC 250 to 400 µg/dL
  • saturation 14% to 50%
  1. Check the inputs: same specimen, both in µg/dL.

    Both formulas need values from one specimen in one unit, or the answer describes neither.

  2. Add them: TIBC = 40 + 380 = 420 µg/dL.

    Total capacity is the bound iron plus the capacity still free.

  3. Divide: 40 ÷ 420 = 0.0952.

    Saturation asks what share of the capacity already holds iron, so the iron is divided by the total.

  4. Multiply by 100: 9.52%, reported as 9.5%.

    The fraction becomes a percentage, rounded once at the end.

  5. Compare: TIBC 420 µg/dL is above 400 µg/dL (High), and 9.5% is below 14% (Low).

    The calculated values go on the report with flags like any measured result.

TIBC is 420 µg/dL (High) and transferrin saturation is 9.5% (Low).

Practice this skill

Your turn

Problem 1 of 3 · Hints available

A procedure calculates TIBC by multiplying transferrin in mg/dL by 1.18. If serum transferrin is 300 mg/dL, what TIBC does the procedure give?

Incorrect. Dividing 300 by 1.18 gives about 254. The stated procedure requires multiplication.

Incorrect. 423 uses the theoretical factor 1.41. This question explicitly supplies the procedure’s factor of 1.18.

Correct. 300 × 1.18 = 354 µg/dL.

Hint
  1. The procedure names its factor. Use that one.
  2. Transferrin is already in mg/dL, so no unit conversion comes first.
  3. Apply the factor the way the procedure states it: multiply.

Review Iron capacity and saturation

Problem 2 of 3 · Hints available

A serum specimen has an iron of 120 µg/dL and a UIBC of 190 µg/dL. What is the TIBC?

Hint
  1. TIBC counts all of the capacity, filled and empty.
  2. The iron is the filled part and the UIBC is the empty part.
Show the answer

310 µg/dL

TIBC = serum iron + UIBC = 120 + 190 = 310 µg/dL.

Review Iron capacity and saturation

Problem 3 of 3 · On your own

A serum specimen has an iron of 180 µg/dL and a UIBC of 60 µg/dL. What is the transferrin saturation?

Show the answer

75 %

TIBC = 180 + 60 = 240 µg/dL, and 180 ÷ 240 × 100 = 75%, above the example interval of 14% to 50%.

Review Iron capacity and saturation

For reference

Sources checked