Difference in Reactivity to Biuret Reagent between Albumin and Immunoglobulin G, and Interference of Bilirubin in the Dual Wavelength Biuret Method

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Biuret method has widely been used for the determination of serum protein concentration in the clinical laboratory. This study demonstrates some of the disadvantages of this method when the dual wavelength procedure is introduced. The absorption maximum of albumin and immunoglobulin G were 542 and 548 nm, respectively, and the difference in absorption curves between these was largest in the range of 600 to 620nm. This difference caused an under-estimation o serum protein concentrations in patients with monoclonal gammopathies and liver cirrhosis when 600nm was used as the reference wavelength. Bilirubin oxidized by biuret reagent had an absorption spectrum in the range of 630 to 950 nm. Therefore, when the range of 650 to 750nm was used as the reference, serum protein concentrations of subjects with elevated (>100mg/l) serum bilirubin were 2-13g/l lower than those determined by the single wavelength (545nm) method. These limitations of the dual wavelength biuret method should be taken into consideration in the clinical laboratory.
Japan Society of Clinical Chemistryの論文