Transferrin is the plasma protein that binds iron and delivers it to the bone marrow, liver and other tissues. Measuring it shows the capacity of that transport system directly, where total iron binding capacity infers the same thing indirectly. It is made in the liver, so it also reflects liver synthetic function and general nutritional state.
No readings for this marker yet.
Raised transferrin is most often a response to iron deficiency, and is also seen in pregnancy and with oestrogen-containing medication. Lowered transferrin most often points to chronic inflammation, infection, liver disease, protein loss through the kidney or gut, or malnutrition, since it is a negative acute-phase protein and falls when inflammation is present. Both directions describe supply and demand for iron transport rather than a diagnosis in themselves. A single unexpected value is a reason to re-test and take the panel to a doctor.
Inflammation of any cause lowers it independently of iron status, while pregnancy, contraceptives and hormone therapy raise it, so timing relative to illness matters more than time of day. It is interpreted with serum iron and ferritin, and most usefully through transferrin saturation, which combines transferrin with circulating iron; total iron binding capacity measures essentially the same protein pool and the two are not read as independent findings.
Reference ranges are general adult values and depend on lab, assay, age and sex. For orientation, not diagnosis — discuss results with your doctor.