A rapid double antibody non-equilibrium serum thyrotropin radioimmunnoassay suitable for primary neonatal hypothyroidism screening.

An improved double antibody radioimmunoassay for measuring human thyrotropin (h-TSH) in serum, suitable for neonatal primary hypothyroidism screening is described. The assay employs a non-equilibrium double antibody technique performed at an initial 37 degrees C followed by incubation at room temperature. Studies on the effects of various reaction parameters including time, temperature, antigen and antibody concentrations and the effect of various carrier proteins on the performance of standard curves were also performed. Using a 100-microliter serum sample for analysis, the assay sensitivity is routinely between 3 and 6 microU/mol of h-TSH (MRC 68/38) with interassay and intra-assay coefficient of variation values ranging from 6 to 14% over a wide range of control values. The incubation and phase separation is completed after 26 h with data available following automated counting and computation. Such a rapid assay facilitates a neonatal screening program for the early detection and treatment of primary neonatal hypothyroidism using either cord blood serum or early follow-up serum sampling in infants suspected on initial screening tests of an abnormality.