Relationships between Serum Total Iron‐Binding Capacity and Transferrin

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Abstract
The relationship between serum transferrin ( TFN ) and serum total iron-binding capacity (TIBC) in a clinical setting was evaluated in two related studies. The initial study evaluated 101 blood samples representing a cross-section of hospitalized adults. The samples were double assayed for TIBC using clinical and research methodologies. TFN was assayed by a commercial radial immunodiffusion method. Clinical laboratory TIBC correlated well with research laboratory TIBC (r = 0.87, slope = 0.97, p less than 0.001, n = 50) and the relationship of TIBC to TFN yielded the following equation: TFN = 0.83 TIBC -5.6 (r = 0.82, p less than 0.001, n = 101) where TFN = mg/100 ml and TIBC = micrograms/100 ml. The second study evaluated a new TIBC assay and its effect on the TIBC/ TFN relationship. Additionally, the TFN -TIBC relationship was evaluated at low normal and abnormal TIBC levels. In this second study, TFN = 1.0 TIBC -18.8 (r = 0.88, p less than 0.01, n = 126). Subsample analysis for specimens with TIBC between 105 and 160 showed a TIBC- TFN regression line that was not significantly different than the entire sample. Inclusion of ancillary patient data such as hemoglobin and hematocrit did not improve the relationship between TFN and TIBC in either study. The relationship was unaffected by age, sex, race, disease, treatment, fever, surgery, degree of nutritional support, blood transfusion, or blood chemistry parameters in either study. Laboratories deriving TFN from measured TIBC as a nutritional status indicator must determine the relationship for the specific procedures being used in their laboratories.