Screening for congenital hypothyroidism. Results in the newborn population of New England.

During the first year of operation, the New England Regional Hypothyroidism Screening Program determined the concentration of thyroxine (T4) levels in dried blood on filter paper from 129,028 infants born in Connecticut, Maine, Massachusetts, New Hampshire, and Rhode Island. Specimens from approximately 3,800 neonates were found to have levels of T4 below the lower limit of normal (less than 6.0 microgram/dl) and were assayed for thyroid-stimulating hormone (TSH) content. Levels of TSH were elevated (greater than 20 muU/ml) in 31 infants, 23 of whom eventually proved to have unequivocal hypothyroidism. Based on these figures and including two hypothyroid infants who were not tested, the incidence of congenital hypothyroidism in the New England region is approximately 1:5,200 births. The estimation of T4 values supplemented by measurement of TSH values on specimens with low T4 values has proved to be a satisfactory approach to large-scale screening for congenital hypothyroidism.