Transferrin saturation (TSAT) is a simple ratio calculated from two common lab values — serum iron and total iron binding capacity (TIBC) — that gives a fast snapshot of how saturated the blood's iron-transport system is. It is one of the first-line tests used to screen for both iron deficiency and iron overload conditions like hereditary hemochromatosis.

How TSAT works

TSAT is calculated as serum iron divided by TIBC, multiplied by 100 to express it as a percentage. Serum iron reflects the iron currently bound to transferrin at the moment of the blood draw, while TIBC reflects the total capacity of transferrin to bind iron — a value that rises when the body senses low iron stores and falls with iron overload or systemic inflammation. Dividing one by the other cancels out some of the day-to-day variability in either value alone, which is part of why TSAT is a more stable screening metric than serum iron by itself.

Inputs and what they mean

Both inputs are entered in micrograms per deciliter (µg/dL), the standard US lab-reporting unit. Typical adult reference ranges are roughly 60–170 µg/dL for serum iron and 250–450 µg/dL for TIBC, though exact ranges vary by lab. A low serum iron with a high TIBC (the body trying to bind more iron than it has) produces a low TSAT and points toward iron deficiency. A high serum iron with a normal or low TIBC produces a high TSAT and points toward iron overload.

Limits and edge cases

TIBC must be greater than zero — a blank field or a lab-entry error of 0 cannot produce a meaningful ratio, so this calculator shows a partial "enter a value" state rather than a nonsensical result in that case. More importantly, TSAT alone does not diagnose iron deficiency or hemochromatosis: it should always be interpreted together with ferritin, which reflects stored iron rather than circulating transport iron, and with the full clinical picture. Serum iron also follows a diurnal pattern and can be affected by recent food intake, so a fasting morning sample gives the most reliable result. This calculator is for educational and clinical decision support purposes only and does not replace a clinician's interpretation.