Optimum laboratory test combinations for thyroid function studies, selected by discriminant analysis.

In 430 patients with a variety of thyroid disorders, linear discriminant analysis was used to select laboratory test combinations giving optimum diagnostic efficiency in thyroid function studies. Unexpectedly, TSH was found valuable in the diagnosis of hyperthyroidism and T3 in hypothyroidism. These test combinations were found optimal for the separation of euthyroidism/hyperthyroidism: T3, TSH and T4; euthyroidism/hypothyroidism: Combined free thyroid hormone index (FTI) and TSH; and hyperthyroidism/euthyroidism/hypothyroidism: T3, TSH, T4, FTI and T3U. The latter test combination had a total efficiency of 94%. Cholesterol, achilles reflex time, PBI and radioiodine uptake measurement contributed little to the discrimination.