A procedure for the redefinition of equivocal results in thyroid function tests.

A retrospective analysis has been made of patients who had been classified (on the basis of measurements of serum thyroxine and thyroid hormone uptake test) as equivocal thyrotoxic (273 patients) or as equivocal hypothyroid (352 patients). The final diagnosis of these patients has been traced from their medical records. The results illustrate that control groups of euthyroid, thyrotoxic, and primary hypothyroid subjects differ from these equivocal groups. The populations initially classified as equivocal have been used to redefine the combinations of values obtained in the serum thyroxine and thyroid hormone uptake test which must be classed as equivocal. Using this redefinition, it is shown that a number of additional tests had been carried out when it could now be predicted with confidence that no useful new information would be obtained. The procedure described is not limited to tests of thyroid function and could easily be applied in most laboratories to redefine the ranges of results classified as equivocal.