Three-year follow-up of borderline congenital hypothyroidism

The purpose of this study was to determine whether children with borderline hypothyroidism in the neonatal period had persistent hypothyroidism after 3 years of levothyroxine replacement therapy. Fourteen term infants with sl ightly abnormal newborn screening results (thyroxine <10th percentile, thyr oid stimulating hormone [TSH] <40 mu U/mL) were identified. The subsequent serum confirmatory TSH results of 12 subjects were modestly elevated (5.3 t o 18.8 mu U/mL, normal 0.6 to 4.6), whereas 2 subjects who had borderline c onfirmatory: TSH (4.6 and 4.7 mu U/mL) had abnormal TSH responses to thyrot ropin releasing hormone testing. After 3 years of therapy, levothyroxine wa s discontinued in 13 patients, and repeat thyroid function tests were obtai ned 1 month later. Levothyroxine was not discontinued in one patient becaus e he had an elevated random TSH (10 mu U/mL) while receiving therapy. At 3 years of age, 13 patients had persistently abnormal thyroid function tests (TSH >4.6 mu U/mL or a thyroid releasing hormone test result consistent wit h primary hypothyroidism), and levothyroxine was reinitiated. Only one pati ent had normal thyroid function studies. Although prospective studies are s till lacking, we recommend levothyroxine replacement in neu borns with bord erline hypothyroidism. (J Pediatr 2000; 136:53-6).