Transferrin level derived from total iron-binding capacity: is it a reliable relationship?

Serum transferrin is an important protein used to assess visceral protein status in patients requiring nutritional support. Since serum transferrin assays are not readily available in all institutions and there is a correlation between the serum transferrin level and TIBC, Blackburn's formula to compute the serum transferrin level is widely used. To evaluate the relationship between TIBC and serum transferrin, as described by Blackburn et al, we observed the TIBC and serum transferrin levels of 91 patients at our institution. Rajamaki et al [14] and Miller et al [13] have suggested that when Blackburn's formula was used, there was a significant difference in actual and derived serum transferrin values. Our formula, derived from such a comparison, approximates Blackburn's more closely than those of Rajamaki et al [14] and Miller et al [13]; however, they are still statistically significantly different. We agree with Miller et al, that each institution using serum transferrin as a nutritional index should either derive its own formula by regression analysis or should determine the actual serum transferrin level with radial immunodiffusion kits.