Congenital hypothyroidism detected by a screening program with specimen collection at two time periods

Abstract

The Northwest (U.S.) Regional Screening Program (NWRSP) for congenital hypothyroidism (CH) employs a primary T4 screen with TSH backup. Heel prick filter paper specimens are routinely collected at 2 time periods: days 1-7 of life and 2-6 weeks of age. Between 5/75 and 3/81, 470,750 infants were tested on the first specimen, while 266,200 were tested on the second specimen. 101 infants were detected with primary hypothyroidism (1:4660), 2 infants had hypopituitary hypothyroidism, while 78 infants were detected with congenital TBG deficiency (1:6035). Of the 101 infants, 90 were detected with a low T4 and elevated TSH on the first specimen (1:5,230), while 11 infants were discovered with a low T4 and high TSH on the second routine specimen (1:24,200). Of these 11 infants, 7 had a T4 concentration above the 3% cutoff on the initial specimen while the other 4 had a T4 below the cutoff, but their TSH concentrations were below the level of sensitivity of the TSH assay (usually <25 μU/ml). Tc99m scans done in 9 of 11 infants showed some residual thyroid tissue in 8 of 9 cases. Six of 7 infants had normal skeletal maturation on X-ray studies. We conclude that 10% of infants with CH appear to have an evolving hypothyroidism which is detected only by a second routine screening test at 2-6 weeks of age. The frequency of detection of CH on the second routine specimen has proven cost-effective in the NWRSP.