Iron saturation, or transferrin saturation (TSAT), reflects the percentage of transferrin binding sites currently occupied by iron. The typical reference range is about 20–50%.

Low TSAT suggests that not enough iron is available for red blood cell production, which may indicate iron deficiency or functional iron restriction in the setting of inflammation. Higher values can raise concern for iron overload. Compared with serum iron alone, TSAT is more clinically useful because it better captures iron availability. In healthy individuals, it is one of the most practical markers for assessing whether iron stores are actually accessible to the body.