Nation-wide TSH-screening with low recall rate. Laboratory results of a two-year study

The laboratory results from the Danish neonatal TSH screening programme for congenital hypothyroidism are reported for a period of 2 years. The screening was based on a single determination of TSH in blood samples taken on the fifth day of life (PKU-filterpaper). The TSH assay (double antibody radioimmunoassay) has a sensitivity of 10 mU TSH/1 blood and a precision of 20-30%. 127,111 samples have been tested. In 3% TSH was greater than 10mU/1 and in 0.64% greater than 25 mU/1. The cut-off point was fixed at 25 mU TSH/1. Values above this level were corroborated by a T-4 radioimmunoassay on the original blood specimen. TSH greater than 25 mU/1 together with T-4 less than 45 nmol/1 blood was found in 37 samples. In 18 samples with TSH greater than 25 mU/1 there was no material left for the T-4 determination. These 55 samples (37 + 18) resulted in a request for a venous sample (recall rate 0.043%). An elevated TSH was verified in 32 of the 55 samples. The repeat samples were collected on average on the 25th day after birth. Three of the 32 babies were clinically diagnosed before the screening result was available.