What Is Transferrin Saturation?
Transferrin saturation (TSAT) is the percentage of transferrin — the main iron-transport protein in blood — that is currently bound to iron. It reflects how much iron is available for the body to use and is a core part of an iron-studies panel, alongside serum iron, TIBC, and ferritin.
A low TSAT points toward iron deficiency, while a high TSAT points toward iron overload. Because it is a ratio of two measured values, you need both the serum iron and the TIBC from the same blood sample.
Transferrin Saturation Formula
TSAT is serum iron divided by total iron-binding capacity, expressed as a percentage:
TSAT% = (Serum iron ÷ TIBC) × 100 Serum iron and TIBC must be in the same unit. If your report uses µg/dL, keep both in µg/dL; if it uses µmol/L, keep both in µmol/L. You can convert each value first with the serum iron converter and the TIBC converter if they are reported in different units.
How to Interpret Transferrin Saturation
These are general educational bands; reference ranges differ by laboratory and clinical situation. Always compare with the range on your own report.
| TSAT | Interpretation | Notes |
|---|---|---|
| Below ~16% | Low — suggests iron deficiency | Often paired with low ferritin |
| ~16–50% | Within the usual adult range | Reference ranges vary by lab and sex |
| Above ~50% | High — suggests iron overload | Consider hemochromatosis; check ferritin |
Reference ranges also differ by sex. Commonly cited adult values are:
| Group | Reference transferrin saturation |
|---|---|
| Adult males | 15–50% |
| Adult females | 12–45% |
Ranges differ for children and for patients on hemodialysis, so always use the reference interval printed on your own report.
TSAT is most useful read together with ferritin, which reflects iron stores: low TSAT with low ferritin supports iron deficiency, while high TSAT with high ferritin supports iron overload.
Alternative Formula (Using Transferrin)
If your report gives serum transferrin instead of TIBC, you can estimate TSAT directly from it. Switch the calculator's method to "Serum iron + transferrin," which uses:
TSAT% = (Serum iron [µg/dL] ÷ Transferrin [mg/dL]) × 70.9 For example, serum iron 112 µg/dL with transferrin 219 mg/dL gives (112 ÷ 219) × 70.9 ≈ 36%. The two methods usually agree closely because TIBC and transferrin measure the same iron-binding capacity in different ways.
Causes of High and Low Transferrin Saturation
A low TSAT can be caused by an iron-poor diet, impaired iron absorption (such as celiac disease), pregnancy and lactation, hormonal contraceptives, or chronic blood loss. Prolonged low values can progress to iron-deficiency anaemia.
A high TSAT can result from iron-rich diets, iron supplements, increased iron absorption (such as hereditary hemochromatosis), or repeated blood transfusions. Persistently high values may indicate iron overload, which can affect the liver and other organs.
Worked Example
Suppose serum iron is 60 µg/dL and TIBC is 400 µg/dL:
(60 ÷ 400) × 100 = 15% A TSAT of 15% is below the usual lower limit of about 20%, which is consistent with iron deficiency and would typically prompt a look at ferritin and the clinical picture.
Frequently Asked Questions
How is transferrin saturation calculated?
TSAT% = (serum iron ÷ TIBC) × 100. Both values must use the same unit so they cancel.
What is a normal transferrin saturation?
Roughly 20–50% in most adults. Below 20% suggests iron deficiency; above about 45–50% suggests iron overload.
Why is my TSAT low but ferritin normal?
Iron studies can be affected by inflammation, recent meals, and timing. TSAT and ferritin are interpreted together with the clinical context, so discuss mixed results with your provider.
Is transferrin saturation the same as iron saturation?
Yes. "Iron saturation" and "transferrin saturation" usually refer to the same TSAT calculation.
References
- Eleftheriadis T, Liakopoulos V, Antoniadi G, Stefanidis I. Which is the best way for estimating transferrin saturation? Renal Failure. 2010.
- Merck Manual Professional Edition — Iron Deficiency Anemia (iron studies and transferrin saturation reference values).
Conclusion
Transferrin saturation is a quick ratio — serum iron over TIBC, times 100 — that helps flag iron deficiency or overload. Use this calculator with your full iron panel and ferritin, and rely on your healthcare provider to interpret what the result means for you.