Cord blood thyrotropin screening for congenital hypothyroidism. Three years' experience on the Island of Saint Lucia.

Cord blood thyrotropin (TSH) screening for congenital primary hypothyroidism has been in effect on the island of St. Lucia for the past three years. Umbilical cord blood samples are obtained on Guthrie filter paper and then transported 3,000 miles to Loyola University of Chicago and delivered to the Illinois State Metabolic Screening Laboratory. There TSH is measured by radioimmunoassay (RIA). After three years, 1,789 newborns have been screened, and the mean value is 6.23 +/- 0.13 microIU per ml. This mean value is less than previously reported by us in 1986 (10.23 +/- 0.29 microIU per ml).13 It is concluded that this screening service continues to be possible far removed from the population under observation. No case of primary hypothyroidism has been detected. Our decreased mean TSH value is due to the new method currently used by the Illinois State Metabolic Screening Laboratory. Congenital hypothyroidism will not be missed provided internal controls are established and rigidly observed.