What iron saturation is
Transferrin saturation (TSAT) = (serum iron / total iron-binding capacity) × 100. It reflects what percentage of transferrin's iron-carrying capacity is currently occupied.
Reference ranges
- Optimal: 25-45%
- Low: <20% (iron deficient or restricted)
- High: >50% (overload or hemochromatosis)
Interpretation patterns
| Pattern | Likely cause |
|---|---|
| Low ferritin + low TSAT | Iron deficiency |
| Normal ferritin + low TSAT + high CRP | Functional iron deficiency (inflammation) |
| High ferritin + high TSAT | Iron overload (consider hemochromatosis) |
| High ferritin + normal TSAT + high CRP | Inflammation-elevated ferritin without overload |
| Normal ferritin + normal TSAT | Adequate iron status |
When to use
- Standard iron evaluation (alongside ferritin and CBC)
- When ferritin is ambiguous in inflamed patient
- Suspected iron overload
- Hemochromatosis screening
The clinical pearl: Iron saturation plus ferritin plus hs-CRP is the cleanest way to determine iron status. Single-marker interpretation often misleads.
Bottom line
Iron saturation complements ferritin. Combined interpretation with inflammation markers gives the clearest iron picture. Standard iron panels include both.
25-45%
optimal TSAT
Combined
with ferritin for clearest picture
>50%
overload investigation threshold