What is the formula to calculate transferrin saturation (Total Iron-Binding Capacity)?

How to Calculate Transferrin Saturation

Transferrin saturation is calculated by dividing serum iron concentration (μg/dL) by total iron-binding capacity (TIBC, μg/dL) and multiplying by 100 to express the result as a percentage. 1, 2

The Formula

TSAT (%) = (Serum Iron / TIBC) × 100 1, 2, 3

• Both serum iron and TIBC must be measured in the same units (typically μg/dL or μmol/L) 1
• The result represents the percentage of transferrin binding sites occupied by iron 1, 3

Alternative Calculation Method

If transferrin concentration is measured instead of TIBC, you can convert it using this formula:

TIBC (μmol/L) = Transferrin (g/L) × 25.1 2, 3

• Some laboratories measure transferrin immunochemically rather than TIBC chemically 4, 5
• After conversion, use the standard TSAT formula above 2

Understanding the Components

Serum Iron

• Measures total iron in serum at the time of blood draw 1
• Highly variable: increases after meals, decreases with infection/inflammation 1, 3
• Shows significant diurnal variation (rises in morning, falls at night) 1, 3

Total Iron-Binding Capacity (TIBC)

• Reflects the availability of iron-binding sites on transferrin 1, 2
• Increases when iron stores are low (more empty binding sites available) 1
• Decreases when iron stores are high 1
• Less variable day-to-day than serum iron 1

Clinical Interpretation

• Normal range: 20-50% 2, 3
• <16-20%: Indicates iron deficiency 1
• >50%: May indicate iron overload 2, 3

Important Timing Considerations

• Do not measure iron parameters within 4 weeks of intravenous iron administration, as circulating iron interferes with the assay 1
• Wait 4-8 weeks after IV iron before checking TSAT and ferritin 1
• For oral iron trials, allow adequate time for response before rechecking 1