A sensitive and practical competitive radioassay for plasma biotin.
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 [(125)I]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 [(125)I]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 microL 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 intra and 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.
Harthé
Catherine
C
Service de Radiopharmacie et de Radioanalyse, Centre de Médecine Nucléaire, 59 Blvd Pinel, 69394 Lyon Cedex 03, France.
Claustrat
Bruno
B
D000328:Adult; D001710:Biotin / Q000008:administration & dosage / Q000097:blood* / Q000172:deficiency*; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D008297:Male; D008875:Middle Aged; D011485:Protein Binding; D011869:Radioligand Assay; D012016:Reference Values; D015203:Reproducibility of Results; D019809:Streptavidin
D007457:Iodine Radioisotopes; D001710:Biotin; D019809:Streptavidin