Enzyme immunoassay of TSH in dried blood, its application to mass-screening of primary hypothyroidism (author's transl)

Abstract

Enzyme immunoassay (EIA) for Thyroid Stimulating Hormone (TSH) has been developed. A principle of the assay was the competitive method and used a double antibody solid phase technique. TSH-horse radish peroxidase (HRP) conjugate and TSH-beta-D-galactosidase (beta-Gal) conjugate were used, and a fluorometry was introduced for measuring the activity of the enzyme. The substrates for determining the enzyme activities were 4-methylumbelliferyl-beta-D-galactoside for beta-Gal, and 3-p(hydroxyphenyl)-propionic acid for HRP. A polyacetal bead coated with a purified double antibody was used for the separation of Bound and Free. With the assay methods, TSH in two of 3mm discs of dried blood on filter paper was measurable. The whole process was completed within 24 hours. TSH standards containing 0.05 microU/tube showed 80 approximately 90% of B/Bo, and the containing 0.25 microU/tube showed about 50% of B/Bo. As a routine method for mass screening of primary congenital hypothyroidism, the EIA method using TSH-beta-Gal was adopted. A variation resulting from day to day experiments was 4.7 approximately 9.4% at B/Bo during a seven day trial. From April of 1980, 12357 samples of newborn blood on filter paper were measured, and a distribution of the value of TSH in dried blood was almost the same as that obtained by RIA. Three cases of cogenital hypothyroidism were detected, and about 0.15% of the total samples showed a TSH concentration higher than 20 microU/ml of whole blood. All the samples were determined by RIA too, and the TSH values obtained from the EIA method were compared to that obtained from the RIA method. The correlation of both EIA and RIA methods was analyzed. Although there were slight discrepancies between EIA and RIA, the samples having high TSH values with the RIA method were all detected by the EIA method. Therefore, the EIA method will be usable as a tool for the mass-screening for the detection of primary congenital hypothyroidism.