Plasma thyroglobulin measurements help determine the type of thyroid defect in congenital hypothyroidism.

Plasma thyroglobulin (Tg) measurements were conducted in infants with congenital hypothyroidism to determine their value in the classification of the thyroid defect. Twenty hypothyroid patients were examined before 50 days of age. Plasma T4, T3, TSH, and Tg were measured and a thyroid scan was performed on all the infants. On the basis of clinical evaluation and the thyroid scans, patients were divided into three groups: group I, ectopic or eutopic hypoplastic glands (n = 11); group II, goiters (n = 3); group III, athyreosis (n = 6). There were no differences among the mean (+/- SD) TSH values of the three groups (377 +/- 291, 402 +/- 202, and 757 +/- 421 microU/ml for group I, II and III respectively). The mean (+/- SD) plasma T4 and T3 levels were lower in group III patients than in the other groups [T4, 0.55 +/- 0.12 vs. 5.0 +/- 3.5 micrograms/100 ml (group I) and 2.7 +/- 1.9 micrograms/100 ml (group II); T3, 29.3 +/- 23 vs. 165 +/- 83 ng/100 ml (group I) and 220 +/- 150 ng/100 ml (group II). Plasma Tg was undetectable in all six infants with athyreosis, and varied from 15-600 ng/ml in group I patients (mean +/- SD, 125 +/- 171 ng/ml). Tg was undetectable in one infant with congenital goiter. We conclude that tg measurements are of value in the classification of infants with congenital hypothyroidism to help clarify the nature of the thyroid abnormality once hypothyroidism has already been diagnosed.