Thyroid function in neonatal hypothyroidism.

Various aspects of the thyroid function have been measured in 28 cases of neonatal hypothyroidism detected by means of the Quebec Screening Program for Metabolic Diseases. In all instances the T4 value in the blood of filter paper spot was below 2 SD of the mean of the day, averaging 0.39 +/- 0.04 ng/40 mul (mean +/- SEM) of eluted blood. The T4 value of a second similar sample averaged 0.22 +/- 0.04 ng/mul of eluted blood; this value was significantly lower than the first one. The serum T4 concentration was decreased in all the infants, whereas three of them had a normal serum TSH concentration. At least three groups of patients could be identified: (1) patients with primary thyroid failure, (2) those with secondary or tertiary hypothyrodism, and (3) those with abnormal synthesis of thyroid hormone.