Studies on the required analytical quality of TSH measurements in screening for congenital hypothyroidism.

In the present study analytical reliability has been evaluated from the point of view of medical practice. The data were obtained from a screening program for congenital hypothyroidism in newborns using measurements of TSH. The aim of the investigation has been to evaluate the optimal analytical quality of the TSH determinations in the classification of children into two groups, with and without hypothyroidism. Evaluation of analytical quality was attempted at four different levels: (i) the numbers of misclassifications at a certain fixed value of the cutoff point, (ii) the numbers of false positives when the percentage of false negatives is fixed, (iii) the total costs of the screening program, and (iv) the social costs. When the evaluations are performed at level (i) and (ii) the results indicate a need for a high analytical quality. At level (iii) a lower analytical quality is acceptable from consideration of costs only. When social costs (iv) are considered, the acceptable analytical quality will depend on the weights given to the different factors. Finally the results point to a close relationship between the imprecision and the cutoff point chosen.