Transferrin-derived TIBC, a flagged but normal result.

BACKGROUND

Total Iron Binding Capacity (TIBC) is routinely used in the diagnosis and management of iron disorders. TIBC can be derived by multiplying transferrin value by a conversion factor. Usage of different conversion factors in calculating patient TIBC results and the upper- and lower-limit of TIBC reference intervals inadvertently exist. Its commonality and effect on diagnosis and clinical management remain unknown.

METHODS

Electronic medical records and laboratory operation procedures were examined to identify and analyze the root of cause of discordant patients' results between transferrin and transferrin-derived TIBC. Internet-searching was conducted for the information, posted on-line by 21 randomly selected CLIA-certified clinical laboratories in the USA, on the conversion factors for calculation of the lower- and upper-limit of TIBC reference intervals.

RESULTS

Discordance between the transferrin and transferrin-derived TIBC results were found to cause no adverse impact on quality of patient care. Of the 21 laboratories, 14 (66%) used different conversion factor values ranging 0.74-1.44 for calculating lower-limit of TIBC reference interval, and 1.07-1.42 for the upper limit, with the absolute difference values ranging 0.01-0.67.

CONCLUSION

Our study suggested that usage of different conversion factors in calculating the upper- and lower-limits of TIBC reference intervals be commonly used by the CLIA-regulated clinical laboratories in the USA but remain unnoticed. The phenomenon of discordant results may likely occur to transferrin results near the lower- or upper-limit of reference range and unlikely cause adverse impact on quality of patient care.