Later manifestations of congenital hypothyroidism predicted by slightly elevated thyrotropin levels in neonatal screening

Abstract Introduction: Neonatal screening programs for congenital hypothyroidism (CH) have been implemented worldwide and have been very successful in identifying infants with CH for thyroid replacement therapy and prevention of developmental delay. False-negative screening results occur, however, and one issue is the optimal cutoff level for thyrotropin (TSH) that will avoid such results. We describe our results in identifying CH by employing a lower than usual cutoff value for TSH. Methods: TSH was measured in newborn dried blood specimens by radioimmunoassay. The cutoff levels of TSH in the initial specimen varied from about 7 to 18 μU/ml of blood because of a floating cutoff level (i.e., in the upper third percentile in the same day's assay run). Results: Thirteen patients with mild CH and seven patients with moderate to severe CH but with delay in developing marked TSH elevation had slightly elevated TSH (less than 20 μU/ml of blood) in the first and/or second specimens. Eleven of the 13 patients with mild CH were confirmed as having primary CH at the ages of 3 to 6 years. Discussion: The cutoff level for TSH in neonatal screening for CH should be lowered sufficiently to detect mild CH and CH with delay in marked TSH elevation. This would decrease the number of false-negative cases.