Transferrin concentration and total iron binding capacity (TIBC) are currently used to assess iron status. Although correlation between TIBC and transferrin is generally considered as good, conversion factors between the two analytes found in literature show large differences. Although the price per test is lower for TIBC, there are a number of analytical advantages of serum transferrin. Due to binding of iron to other plasma proteins (mainly albumin), TIBC methods generally overestimate the iron binding capacity of transferrin. Moreover, no generic reference values are available for TIBC. In contrast to TIBC, internationally accepted interim reference ranges are available for serum transferrin. The introduction of the international CRM 470 protein standard material has lead to a significant reduction in interlaboratory variation for transferring measurements. In view of these observations, determination of transferrin concentration, rather than TIBC, is recommended. However, in non-European populations characterized by a marked genetic variation in transferrin (TF BC and TF CD variants), in certain cases, immunochemical determination of transferrin may lead to errors. In these populations, TIBC measurements may be preferred.