Transferrin Saturation: How Well Does Your Body Transport Iron?

Transferrin saturation, also written as TSAT or transferrin percent saturation, is the percentage of your transferrin that is actually carrying iron. It is calculated by dividing your serum iron by your total iron-binding capacity (TIBC) and multiplying by 100.

Transferrin is the protein that transports iron through your blood. When your iron stores are low, more transferrin travels empty and the saturation falls; when there is too much iron, the saturation rises. That makes it a more complete picture of iron status than serum iron or transferrin measured alone.

A normal transferrin saturation is roughly 20 to 45 percent, though the exact range depends on the laboratory and on the time of day the blood was drawn.

Transferrin saturation is one of the most informative markers for assessing iron balance. Because it reacts before your red blood cells change, it can help identify iron deficiency early, often together with a low ferritin.

A low saturation typically fits iron deficiency, blood loss or increased demand. A high saturation can point to iron overload, as in the hereditary condition haemochromatosis, where the body absorbs and stores too much iron.

Because a single value shifts with meals, iron supplements and the time of day, the saturation is best read together with your ferritin and repeated when needed rather than judged on one measurement.

Testing may be recommended when iron deficiency or iron overload is suspected, as part of anemia investigation, during monitoring of iron supplementation, or as a screening tool for hereditary hemochromatosis.