Twenty years later: a reevaluation of the contribution of plasma thyroglobulin to the diagnosis of thyroid dysgenesis in infants with congenital hypothyroidism

Background: The definition of the type of thyroid dysgenesis in congenital hypothyroidism (CH), ectopy, or athyreosis is important for monitoring patients and for genetic investigations. We have recently encountered infants who in spite of undetectable Technetium uptake on scintigraphy had biochemical results making athyreosis unlikely. Objective: To reevaluate the utility of plasma thyroglobulin (Tg) in this clinical context using new sensitive Tg assays. Subjects and Methods: Plasma Tg was retrospectively determined by two immunoassay systems on specimens obtained at diagnosis in 31 hypothyroid infants with thyroid dysgenesis. Results: Scintigraphy led to the diagnosis of ectopy in 19 infants and of athyreosis in 12. Seven (58%) of the infants classified as athyreotic by scintigraphy had detectable plasma Tg (>0.2 μg/l), indicating that they had functional thyroid tissue. Conclusions: An undetectable plasma Tg should be documented to validate a scintigraphic diagnosis of athyreosis. Conversely, when plasma Tg is undetectable, scintigraphy could be avoided.