Serum thyroglobulin in differential neonatal diagnosis of congenital hypothyroidism. (Valore della concontrazione plasmatica di tireoglobulina nella diagnosi differenziale neonatale di Ipotiroidismo Congenito)

Thyroglobulin (Tg) is a glicoprotein produced by thyroid gland, it represents the storage form for thyroid hormones. In newborns serum Tg concentrations are higher than in adult subjects; during the first year of We Tg levels decrease to wards adult normal range. Because th yroglobulin is secreted only by thyroid cells and it does not cross the placental barrier, serum Tg detection confirms the presence of functioning thyroid tissue in hypothyroid newborn. Measurement of serum Tg in neonatal age has recently been proposed as an useful tool in the dyferential diagnosis of Congenital Hypothyroidism (CH) detected by screening programs. During neonatal age an etiological diagnosis between the various forms of hypothyroidism is important for the therapeutic management follo w-up and prognosis. In order to investigate the role of serum Tg measurement in the diagnosis of thyroid disorders we studied a group of 61 newborns with proved CH due to dUferent thyroid anomalies. In the present study we report the results of serum Tg levels in newborns with thyroid agenesis ( I3 cases), ectopic or ipoplasic gland (33 cases), enzimatic defect (7 cases) and transient hypothyroidism (8 cases). In all patients diagnosis was confirmed by ecographic and radioisotopic scan. Serum Tg was detected by radioimmunoassay before starting replacement therapy; serum antibodies anti- Tg were also determined in all cases. In our patients serum neonatal Tg levels were undetectable (< 2.5 ng/ml) or very low in all cases with thyroid agenesis (p< 0. 001 ). Newborns with ectopic gland or transient hypothyroidism showed normal or moderately elevated serum Tg values (ps NS). In all patients with dysormonogenesis serum Tg concentration was extremely high (p< 0.001). These data indicate that serum Tg measurement may be useful in the dUferential diagnosis of congenital hypothyroidism but cannot differentiate patients with perinatal transient hypothyroidism from normal subjects and from those with permanent congenital hypothyroidism with functioning thyroid tissue (ectopic or ipop/asic gland, d ysormonogenesis with altered metabolism of thyroglobulin). In these cases differential diagnosis needs ecographic and radioisotopic scans.