Enzyme Immunoassay of Thyroid-Stimulating Hormone Using Dried Blood Samples a Simple Technique of Screening for Congenital Hypothyroidism

Abstract

A method for enzyme imnunoassay of thyroid-stimulating hormone (TSH) in dried blood spotted onto filter paper has been developed. TSH was conjugated to horse-radish peroxidase according to Nakane's method. Separation of the bound and free fractions was obtained by a double antibody solid phase method using polyacetal beads which were coated with the purified IgG fraction from goat anti-rabbit IgG serum. p-Hydroxyphenyl propionic acid was used as substrate for the fluorophotometric assay of peroxidase activity. The assay sensitivity is 0.07, μU TSH/assay tube, which is equivalent to μU/ml when five 3 mm discs of dried blood spot are assayed. TSH values in dried blood samples obtained by this method correlate well with those of serum samples obtained by radioimmunoassay (r=0.89). The coefficients of variation were 6.8 to 13.4% (within assay) and 5 to 40% (between assay). The enzyme immunoassay of TSH presented here is applicable to the mass-screening for congenital hypothyroidism of neonate.