Enzyme-linked immunoassay of thyrotropin

A method was developed for immunoassay of thyrotropin after its conjugation with alkaline phosphatase using the double antibody technique. The dilution of serum resulted in curves parallel to those obtained for standard thyrotropin. The mean recovery of thyrotropin (TSH) added to serum was 97%, and values for serum TSH determined by this method correlated well with those determined by radioimmunoassay. The coefficients of variation were 2 to 7% (within assay) and 10 to 15% (between assay). The method requires minimal equipment, and is less expensive than radioimmunoassay, so it should be useful as a screening test for primary hypothyroidism in cases with above the maximum normal serum TSH level (10 μU/ml).