Transferrin
Transferrin is the main protein that carries iron through your bloodstream, delivering it from storage and absorption sites to the tissues that need it. A transferrin test measures how much of this transport protein you have.
Transferrin underlies the whole iron-transport picture: it's what TIBC and UIBC are largely measuring, and it's the protein whose 'fullness' transferrin saturation describes. By showing how much carrier capacity you have, it helps distinguish iron deficiency from other causes of abnormal iron results. It's most informative combined with serum iron and saturation.
A high transferrin level often reflects iron deficiency, as the body typically produces more carrier protein when iron is scarce. Pregnancy and estrogen-containing medications can also raise it. As always, the surrounding iron markers give it meaning.
A low transferrin can be seen with inflammation, chronic illness, liver conditions, or malnutrition, since it depends on nutrition and liver function. It's best understood alongside the rest of your iron results.
Reference ranges vary by lab and can be affected by pregnancy, medications, and nutrition. A clinician can interpret your transferrin in the context of your full iron panel and health.
Sources
Educational context only, not medical advice or a diagnosis. Reference ranges vary by lab, age and sex; always discuss your results with a clinician.