Transferrin

Transferrin is a protein made by your liver that carries iron through your bloodstream to where your body needs it. When your iron levels are low, your liver makes more transferrin to try to capture as much iron as possible. When iron levels are high or if you have liver problems, inflammation, or poor nutrition, transferrin levels tend to be lower. Your doctor uses transferrin along with other blood tests to understand how well your body is managing its iron stores and to help identify conditions like iron deficiency anemia or iron overload.

When elevated: Elevated transferrin is most commonly associated with iron deficiency anemia, reflecting compensatory upregulation of hepatic synthesis to increase iron-binding capacity. It may also be seen in pregnancy and with oral contraceptive use due to estrogen-mediated stimulation of hepatic synthesis. When low: Low transferrin levels suggest reduced hepatic synthetic capacity (as in liver disease or malnutrition), iron overload (hemochromatosis, repeated transfusions), chronic inflammatory states, nephrotic syndrome (urinary loss), or protein-losing enteropathy. Low transferrin in the context of anemia may indicate anemia of chronic disease rather than iron deficiency.

Transferrin is moderately relevant to athletes because iron deficiency impairs oxygen delivery and aerobic performance, while iron overload can increase oxidative stress and inflammation. Endurance athletes, female athletes, and vegetarian/vegan athletes are at higher risk for iron deficiency; monitoring transferrin alongside iron and ferritin helps detect early deficiency before performance declines and supports informed dietary or supplementation strategies.