Total Iron-Binding Capacity

TIBC measures your blood's total capacity to carry iron, which is essentially a stand-in for how much transferrin — the main iron-transport protein — you have available. It doesn't tell you how much iron you're carrying, but how much room there is to carry it. Paired with serum iron, it's used to work out transferrin saturation and to distinguish iron deficiency from iron overload.

A common reference range is roughly 250–450 µg/dL, with some labs quoting a somewhat narrower band. Values above the range often accompany iron deficiency, while values below it can point toward iron overload or inflammation. As with the rest of the iron panel, interpret TIBC against your own lab's range and alongside ferritin and transferrin saturation.

This inverse relationship trips a lot of people up. When the body senses low iron, it makes more transferrin to scavenge whatever iron it can, so binding capacity — TIBC — rises. When iron is overloaded, the body dials transferrin back and TIBC falls. So a high TIBC with low serum iron is a classic iron-deficiency pattern, while a low TIBC with high iron suggests overload.

They measure nearly the same thing from different angles: transferrin is the actual transport protein (reported in mg/dL, typically around 200–360), while TIBC estimates the total iron that all that transferrin could bind (reported in µg/dL). Because TIBC is largely a function of transferrin, the two track closely and a panel usually reports one or the other. Both feed the same interpretation of your iron transport capacity.

Transferrin is the carrier protein, TIBC is the total iron that carrier could hold, and transferrin saturation (TSAT) is the percentage of that capacity currently filled — calculated as serum iron divided by TIBC. So TIBC is the denominator that tells you the size of the tank, and TSAT tells you how full it is. Reading them together with ferritin gives a far clearer iron picture than any single value alone.