Background: Thyroglobulin (Tg), a protein synthesized uniquely in the thyroid gland, may be elevated in primary congenital hypothyroidism (CH) due to increased TSH drive, absent in true athyreosis and Tg deficiency, and very elevated in some types of dyshormonogenesis.
Hypothesis: Serum Tg at the time of newborn screening may reflect the amount of thyroid tissue present in apparent athyreosis and thyroid ectopia, and hence provide a guide as to future levothyroxine (L-T4) requirement. This could be useful in avoiding overtreatment with L-T4.
Design: We studied the relationship between serum Tg at the time of referral in infants with CH due to athyreosis and ectopia, together with L-T4 dose (mg/m2), plasma TSH and free T4 (fT4) at diagnosis, 6 and 12 months.
Results: Median (range) Tg at diagnosis in 26 infants with true (n=9) and apparent (n=17) athyreosis, and ectopia (n=56) was 10 (1.9-58) and 177 (84.7-3977) µg/l respectively (reference range 91.3-148 in 3-day infants). In patients with ectopia, median (range) L-T4 dose (mg/m2) at 6 and 12 months was 102.4 (95.9-121.6) and 98 (83.9-114) respectively. There was a low negative correlation between serum Tg at diagnosis and L-T4 dose at 12 months (rho= -0.407, P=0.02), but no significant correlation at 6 months. In patients with athyreosis, median (range) L-T4 dose (mg/m2) at 6 and 12 months was 97.9 (89.2-103.9) and 109.1 (98-117.6) respectively, with no correlation between serum thyroglobulin and LT4 dose at 6 and 12 months.
Conclusion: As well as being of diagnostic value in some forms of CH, serum Tg at birth may be of value in guiding LT4 dosage during the first year of life especially in patients with thyroid ectopia. However, larger patient numbers and prospective study are needed to offset confounding variables including L-T4 dosing protocols and adherence.
15 Sep 2022 - 17 Sep 2022