Table 8.

Findings in diagnostic studies undertaken to identify the underlying etiology of congenital hypothyroidism

Defect	Radionuclide image	Ultrasonography	Serum thyroglobulin	Maternal TRB-Ab
Aplasia	No uptake	Absent gland	Low	Negative
Hypoplasia	↓ uptake	Small, eutopic	Intermediate	Negative
Ectopia	↓ uptake, ectopic	Ectopic gland (hypoplastic)	Intermediate	Negative
TSHβ mutations	No uptake	Eutopic gland (hypoplastic)	Intermediate	Negative
TSH receptor inactivating mutation	↓ uptake	Eutopic gland	Intermediate-high	Negative
Trapping error	↓ or no uptake	Eutopic gland	Low-intermediate	Negative
Beyond trapping error	↑ uptake	Eutopic, large gland	High Exception: Tg gene mutations	Negative
Maternal TRB-Ab	↓ or no uptake	Eutopic gland	Low-intermediate	Positive