Calculate transferrin saturation (TSAT) from serum iron and TIBC or from transferrin, or solve for TIBC or serum iron, in µg/dL or µmol/L.

Use serum iron and TIBC from the same blood test.

Laboratory comparison interval (optional)
Leave both interval fields blank for no comparison.

Related Calculators

Transferrin Saturation Formula

Transferrin saturation (TSAT) estimates how much of the blood’s iron-transport capacity is currently occupied by iron. It is calculated by comparing serum iron with total iron binding capacity (TIBC) and expressing the result as a percentage.

TSAT = (SI) / (TIBC) × 100
Variable Meaning Typical Unit
TSAT Transferrin saturation %
SI Serum iron concentration µg/dL
TIBC Total iron binding capacity µg/dL

Important: the ratio requires matching iron concentration units. Select the units printed on each report; the calculator converts mixed µg/dL and µmol/L inputs using 1 µmol/L = 5.5845 µg/dL, based on iron atomic weight 55.845 g/mol.

Transferrin is a protein concentration, not TIBC. In transferrin mode, select the conversion supported by the reporting laboratory: TIBC (µg/dL) = transferrin (mg/dL) × factor. Published method conventions differ, including Mayo SFEC 1.18, BIOLABO 1.25 and ELITech 1.4. The legacy 70.9 choice reproduces the older TSAT approximation with factor 100/70.9; it is not a universal laboratory method. Choose a supported method or custom factor, rather than guessing.

Optional comparison bounds must come from the laboratory report. Leave both blank for no comparison. The inverse modes are algebraic calculations: positive iron and positive TSAT identify a finite positive TIBC; zero/zero is nonunique. They do not identify a treatment target.

How to Calculate Transferrin Saturation

  1. Measure the serum iron value.
  2. Measure the total iron binding capacity (TIBC).
  3. Divide serum iron by TIBC.
  4. Multiply the result by 100 to convert it to a percentage.

This calculator can also solve for a missing variable when the other two are known.

SI = (TSAT × TIBC) / (100)
TIBC = (SI × 100) / (TSAT)

Calculation Example

If serum iron is 80 µg/dL and TIBC is 320 µg/dL, then:

TSAT = 80 ÷ 320 × 100 = 25%

The calculated iron-to-TIBC ratio is 25%. Its clinical interpretation depends on the laboratory method and the complete iron panel.

What the Result Means

TSAT is commonly used as part of an iron study panel. By itself, it does not diagnose a condition, but it helps show whether circulating iron appears relatively low, adequate, or increased in relation to transport capacity.

  • Lower TSAT may be seen when available circulating iron is reduced.
  • Higher TSAT may be seen when a larger share of transferrin is carrying iron.
  • Interpretation is strongest when combined with other labs such as ferritin, hemoglobin, hematocrit, red cell indices, and markers of inflammation.

Why TSAT Matters

Transferrin is the main protein that transports iron through the bloodstream. Measuring saturation helps estimate whether iron delivery may be limited or excessive relative to binding capacity. This is useful in evaluations involving:

  • possible iron deficiency
  • possible iron overload
  • anemia workups
  • monitoring response to iron therapy
  • chronic disease states where iron handling may be altered

Factors That Can Affect the Number

TSAT can shift based on biology, timing, and lab conditions. Consider the full clinical context before drawing conclusions from a single value.

  • Recent iron supplementation can temporarily raise serum iron and TSAT.
  • Time of day may affect serum iron measurements.
  • Inflammation or illness can change how iron is stored and transported.
  • Liver disease, hemolysis, or transfusions may alter iron-related results.
  • Non-fasting vs. fasting collection can influence comparability between tests.

Common Input Mistakes

  • Selecting units that differ from those printed on the report, or dividing unmatched units without conversion.
  • Entering transferrin in a TIBC field, or assuming all laboratory transferrin conversion factors are interchangeable.
  • Rounding too early before multiplying by 100.
  • Interpreting a single abnormal value without the rest of the iron panel.

Quick Interpretation Notes

  • A TSAT result is a ratio, not a direct measure of total body iron stores.
  • Ferritin often helps answer the separate question of how much iron is stored.
  • Two people can have the same TSAT but different overall iron status depending on ferritin, blood counts, symptoms, and underlying conditions.

Frequently Asked Questions

Can transferrin saturation be greater than 100%?

A calculated iron-to-TIBC ratio can exceed 100%. Verify the entries, units, specimen and assay methods with the reporting laboratory. This is not literal binding-site occupancy, a diagnosis, or a treatment instruction; do not clamp the reported arithmetic value to conceal a discrepancy.

Is transferrin saturation the same as ferritin?

No. TSAT estimates how much iron transport capacity is currently being used, while ferritin reflects iron storage. They answer different questions and are often interpreted together.

Why can the result change between tests?

Serum iron can vary with timing, recent supplementation, diet, illness, and laboratory conditions. Repeat testing is sometimes needed for a clearer picture.

Should this calculator be used for diagnosis?

This calculator is best used for calculation and education. Medical interpretation should be based on the full iron panel, symptoms, health history, and clinician review.