Objectives: There is little agreement as to the optimal cutoff point for thyrotropin testing in primary thyroxine screening programs for congenital hypothyroidism. Most programs in the United States use a cutoff point of 10% of the lowest thyroxine values, whereas in the Netherlands a cutoff point of 20% is used. Therefore, the results of the Dutch program may provide valuable information about the optimal cutoff point.
Methods: The frequency distribution of screening thyroxine values was studied in all cases of permanent primary congenital hypothyroidism (n = 481) detected in 1,601,603 screened children born during the period from January 1, 1981, to December 31, 1989, in the Netherlands.
Results: Programs using a 10% cutoff point would have missed 1.5% of cases. Above the 10% cutoff point, the marginal costs increase quite rapidly because of the escalating numbers of thyrotropin measurements necessary to detect one case of permanent primary congenital hypothyroidism: 20,000 in the range of 11% to 15% and 40,000 in the range of 16% to 20%.
Conclusions: Based on these findings, a cutoff point of at least 10% is recommended.