IMMUNORADIOMETRIC ASSAY OF THYROTROPIN DURING THE FIRST 6 MONTHS OF LIFE

The aim of this preliminary study was to assess variation in thyrotrop in (thyroid-stimulating hormone; TSH) levels using an immunoradiometri c assay during the first 6 months of life of normal infants. One hundr ed and five normal newborns (59 females, 46 males) were evaluated for TSH, triiodothyronine and thyroxine at 48 h of life, and TSH was addit ionally determined at 15 days (n = 42), 30 days (n = 38), 60 days (n = 24), 90 days (n = 28), and 180 days (n = 30). Complete determinations during the total period of the study were obtained in 17 infants. Sam ples corresponding to the 48-hour period did not exhibit a normal dist ribution. In this group, percentile 3 corresponded to 0.9 mU/l, the me dian to 4.2 mU/l and percentile 97 to 17.7 mU/l. Levels of TSH similar to those of the normal adult population were reached between 30 and 6 0 days of life. Nevertheless, TSH levels of some of the children remai ned at higher values for a longer period. In summary, our results sugg est that high TSH levels might not always indicate an underlying patho logy. A critical evaluation of the normality criteria could avoid unne cessary studies and treatments.