PonyatnoHow it's calculated
Transferrin saturation is serum iron as a share of total iron-binding capacity: TSAT (%) = iron ÷ TIBC × 100, with both values in µmol/L.
If your report has transferrin instead of TIBC, TIBC is estimated with the Gambino (1997) formula: TIBC (µmol/L) = transferrin (g/L) × 25.1. This is an approximation: your lab’s own saturation may differ by a few percentage points.
Units: µg/dL is converted to µmol/L by multiplying by 10 and dividing by 55.845 (the molar mass of iron); transferrin in mg/dL is divided by 100 to get g/L. TIBC and UIBC (TIBC − iron) are shown in µmol/L.
Ranges: below 20% — low, 20–45% — typical, 45% and above — high (the threshold for checking iron overload follows EASL guidelines).
What to know
What transferrin saturation shows
Transferrin is the protein that carries iron in the blood. Saturation shows how full it is: with too little iron there are many empty seats, with too much almost all are taken. It does not show how much iron is stored in the body — that is what ferritin is for, so saturation is read alongside it.
When the result can mislead
Serum iron swings a lot: it is higher in the morning than in the evening and rises after meals, and especially after iron tablets. That is why the test is usually done in the morning on an empty stomach, and iron supplements are paused beforehand if your doctor agrees.
Saturation drops with inflammation and chronic illness even when iron is sufficient. It can read falsely high with a hemolyzed sample, liver disease or after transfusions. One value is not a diagnosis: when it is off, the test is usually repeated.
This calculator is a reference tool, not a diagnosis. Laboratory ranges differ, and the result depends on your health, medicines and other tests. Discuss it with your doctor.
FAQ
What is a normal transferrin saturation?
Usually 20–45%. Your lab may print its own reference range — go by that first.
Does low transferrin saturation mean iron-deficiency anemia?
Not necessarily. Low saturation can point to iron deficiency, but the conclusion is made together with ferritin, hemoglobin and signs of inflammation. Anemia means low hemoglobin, which is checked on a complete blood count.
What does high transferrin saturation mean?
Most often recent iron intake or something about how the blood was drawn. If a repeat morning fasting test confirms it, your doctor may look for iron overload such as hemochromatosis. That can’t be diagnosed from one calculation.
How should I prepare for an iron test?
Come in the morning, fasting. If you take iron supplements, ask your doctor or the lab how long before the test to stop them.
What is the difference between TIBC and transferrin?
Transferrin is the carrier protein itself; TIBC is how much iron it can bind. One can be converted into the other, so the calculator works with either.
Sources
Formulas and cut-offs follow clinical guidelines — see sources below.
- Gambino R et al. The relation between chemically measured total iron-binding capacity concentrations and immunologically measured transferrin concentrations in human serum. Clin Chem. 1997;43(12):2408–2412.
- WHO guideline on use of ferritin concentrations to assess iron status in individuals and populations. Geneva: WHO; 2020.
- EASL Clinical Practice Guidelines on haemochromatosis. J Hepatol. 2022;77(2):479–502.