Background: Biotin is a water-soluble vitamin which plays an important
biochemical role in a variety of carboxylase-mediated metabolic reactions.
Determination of biotin status for the diagnosis of biotin deficiency is crucial.
Methods: We describe a solid-phase protein-binding assay involving
[125I]iodostreptavidin as a tracer for the determination of biotin in
plasma. The assay was conducted in one step by incubation of a fixed amount of
[125I]iodostreptavidin as binding reagent with varying amounts of
biotin, diluted in biotin-free plasma (standard curve) or unknown samples in tubes
previously coated with biotin linked to goat antirabbit IgG. Increasing amounts of
biotin in the standard or unknown samples in tubes previously coated with biotin
occupy more sites on iodostreptavidin, resulting in fewer counts bound to tubes. The
effects of the incubation time and temperature on the competitive binding of biotin
with iodostreptavidin were tested.
Results: The detection limit of the plasma assay for biotin was 100
pmol/L. Only 100 µL of plasma were necessary for the assay, which was performed
within 6 h. The dilutions of plasma and synthetic biotin gave a parallel response.
Plasma biotin levels ranged from 0·49 to 1·33 nmol/L (mean 0·76 nmol/L) in healthy
subjects. The intraand inter-assay coefficients of variation were 3·5% and 10%,
respectively, at a concentration of 0·27 nmol/L.
Conclusions: This assay was suitable for the direct measurement of
biotin in human plasma and was robust and sensitive enough for screening for biotin
deficiency.
