Thyroid screening of neonates without use of radioactivity: evaluation of time-resolved fluoroimmunoassay of thyrotropin.

We evaluated the usefulness, in routine newborn screening for congenital hypothyroidism, of a time-resolved fluoroimmunoassay kit (DELFIA Neonatal TSH) for the determination of thyrotropin (TSH) in dried blood spots. A total of 11 531 dried blood samples from newborns were tested in parallel in each of two Swiss screening laboratories, by RIA and DELFIA. Six cases of confirmed congenital hypothyroidism were detected during the study period. The rate of false-positive results, after single TSH determination in the DELFIA assay, was 0.16%. Correlation of RIA and DELFIA results for TSH was very good in both laboratories (0.959 and 0.97, respectively). The new method fulfills the criteria for precision and sensitivity of a screening assay. Screening results are usually available the day after the sample arrives in the laboratory, thus favoring early diagnosis and allowing treatment to begin by the seventh or eighth postnatal day.