MEASURING THYROXINE AND THYROTROPIN SIMULTANEOUSLY IN A DRIED BLOOD-SAMPLE ON FILTER-PAPER, TO SCREEN FOR NEONATAL-HYPOTHYROIDISM

  • 1 January 1980
    • journal article
    • research article
    • Vol. 26  (6) , 750-753
Abstract
A highly sensitive radioimmunoassay of thyroxine [T4] and thyrotropin [TSH] was developed for mass screening for neonatal hypothyroidism. This assay involves a single disc (3 mm diameter) of dried blood on filter paper. The minimum detectable concentrations are 15 pg/tube (10 .mu.g/l) for T4 and 15 nIU/tube (10 mIU/l) for TSH; intra- and interassay coefficients of variation are < 15% in both assays. The high sensitivity of this method is due to use of labeled T4 with high specific activity (3 kCi/g) and of anti-TSH serum with high affinity (equilibrium constant = 7.8 .times. 1011l/mol). With this method, 11,337 newborns were screened; a follow-up study revealed that only newborns with both high TSH and low T4 concentrations had permanent hypothyroidism. This method is sensitive, simple and reliable and the recall rate with this method is much lower than that of tests for measuring T4 or TSH alone.