Measurement of thyroglobulin in newborn screening specimens from normal and hypothyroid infants

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Abstract
Thyroglobulin (Tg) has been found in varying concentrations in infants and children with congenital hypothyroidism. Our primary goal was to ascertain whether Tg in filter paper blood specimens used for routine newborn screening would be a useful adjunct in the early diagnosis of newborn children with congenital hypothyroidism. Our secondary objective was to correlate the results of the Tg determinations with the results of thyroid scintigraphy in the same cohort of infants with congenital hypothyroidism. An RIA kit with high sensitivity for the measurement of Tg in serum was modified for use with filter paper blood specimens. Results of thyroid scintigraphy were obtained from the family physicians on 10 infants with ectopic thyroid glands and 18 who were considered to be athyreotic. Determinations of Tg were carried out retrospectively on newborn screening filter paper blood specimens from 61 full-term normal infants and 42 newborns with confirmed congenital hypothyroidism. Thyroglobulin concentrations during the first week of life in the normal controls ranged between 17 and 160 micrograms/l, with a median of 66 micrograms/l. Tg values for infants with ectopic thyroid glands ranged between 38 and 282 micrograms/l, with a median of 160 micrograms/l, with a median of 66 micrograms/liters. Tg values for infants who were considered athyreotic had Tg values ranging between undetectable and 104 micrograms/l with a median of 15 micrograms/l. Fifty per cent of the athyreotic patients and 50% of patients with ectopic thyroid glands had Tg values above or below the normal range and thus fell within the diagnostic category of hypothyroidism on the basis of Tg alone. Fifty per cent of patients who were considered athyreotic by scintigraphy had Tg concentrations ranging from 20 to 104 micrograms/l. These studies have shown that thyroglobulin can be measured in the same filter paper blood specimens used for routine newborn screening. Estimation of thyroglobulin in screening specimens from hypothyroid and normal infants indicated that some infants with congenital hypothyroidism could be identified solely on the basis of the thyroglobulin concentration. Comparison of the result of scintigraphy with thyroglobulin levels in the same hypothyroid patients suggested that thryoglobulin provided a more reliable marker for the presence or absence of the thyroid gland than did scintigraphy.