[The estimation of thyroxine, triiodothyronine, thyro-binding-index, and free-thyroxine-index in the newborn (author's transl)].

Because of the importance of early diagnosis of hypothyroidism normal values of thyroxine (T4), thyro-binding-index (TBI), free thyroxine-index (FTI) and triiodothyronine (T3) in the serum of newborns were established. In extremely premature babies as in early fetal life the total thyroxine is relatively low. The lowest serum thyroxine in newborns without hypothyroidism was found in a premature infant with a birth weight of 750 g, i.e. 4.8 mug/100 ml on the 4th day of life. Otherwise the T4 values were quite high during the neonatal period, without signs of hyperthyroidism. Our hypothyroid patients scarcely had higher T4 values (0.8-5.1 mug/100 ml) within the first month of life than older hypothyroid patients. Healthy newborns had a mean T4 value of about 15 mug/100 ml during the first week of life (two standard deviations 6.4-23.6 mug/100 ml). Afterwards the T4 values slowly came down to a mean of about 12 mug/100 ml in the 4th week of life. During the first month of life the FTI of hypothyroid patients was below two standard deviations of normal newborn values, whereas TBI-values showed an overlap. During the first 3 days of life newborns with goiter had T4-values in the lower normal or hypothyroid range without obvious signs of hypothyroidism. FTI was quite low, too, and TBI relatively high (as in hypothyroidism). Within the second week of life all these values normalized mostly after treatment with KI ointment, occasionally without this treatment. Where these values did not normalize, hypohtyroidism was assumed. Triiodothyronine in cord blood was very low (0.47 ng/1.6 ng/ml) during the neonatal period (one to two days after birth almost 2.0 mg/ml). Values in our hypothyroid patients fluctuated widely (zero to slightly elevated values with a mean of 0.78 ng/ml). Therefore, T4 seemed more reliable than T3 for the diagnosis of hypothyroidism (the opposite was true for hyperthyroidism.