[Screening for congenital hypothyroidism with an immunoradiometric assay (IRMA) for thyroid stimulating hormone]

A commercial immunoradiometric assay (IRMA) for thyroid stimulating hormone (TSH) was modified to be used with dried blood on filter paper of our neonatal screening programme. Sensitivity and precision were as good as with the conventional radioimmunoassay (RIA), but the IRMA was faster. In addition the IRMA was extremely cheap, because all kit reagents could be prediluted 1:4. Our screening procedure for congenital hypothyroidism now combines a determination of TSH with the IRMA technic and a determination of free thyroxin (FT4) by radioimmunoassay. The kit for FT4 can be diluted 1:3, as described earlier. The combination of TSH-IRMA und FT4-RIA to our knowledge is not only much faster but also considerably cheaper than measuring one parameter with consecutive retesting of suspicious samples, which is the procedure in some countries. As the combination gives two independent results it is also of greater clinical value than measuring TSH in dublicates, which is still officially recommended in the Federal Republic of Germany.