Comparison of Derived and Actual Transferrin

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Abstract
A prospective study was undertaken to evaluate the utility of calculating transferrin from total iron-binding capacity in the nutritional assessment of burned patients. Regression analysis was used to compare total iron-binding capacity with radial immunodiffusion transferrin determinations. The method used for calculating transferrin (0.8 TIBC – 43) is a frequently published conversion formula for deriving transferrin. One hundred twenty-five data sets were obtained from 45 burned patients. Values for derived transferrin ranged from 39 to 235 mg/dl, averaging 121 mg/dl. Actual transferrin averaged 162 mg/dl, ranging from 41 to 320 mg/dl. Forty-eight actual serum transferrin samples were normal (greater than 172 mg/dl) whereas only 17 derived transferrin values were normal. While there is a correlation between total iron-binding capacity and serum transferrin (r = 0.85), to calculate transferrin according to the formula above would have resulted in significant error in the clinical assessment of the patients' nutritional status (p < 0.001). From our studies, the formula for conversion of total iron-binding capacity to transferrin was found to be (0.68 TIBC + 21). These results suggest that the development of a universal conversion factor is not feasible. Modification of the formula may be necessary at each institution if clinically useful evaluations of serum transferrins are to be derived from iron-binding capacity for use in nutritional assessment.