TIBC is the Total Iron Binding Capacity and measures the amount of iron bound to proteins. Given that the protein transferrin is the primary iron-binding protein, TIBC is an approximate estimation of the serum transferrin level.
UIBC is the Unsaturated Iron Binding Capacity and measures the levels of transferring that has not been bound by transferrin. It has been called the reserve capacity of transferrin.
TIBC is the test that is built into the software and is used to evaluate iromn deficiency anemia. UIBC typically follows TIBC in terms of what it can tell us about iron deficiency anemia. UIBC is not commonly reported on US blood tests but you can calculate UIBC:
UIBC = TIBC – serum iron