Discriminative ability of tests for free and total thyroid hormones in diagnosing thyroid disease

Clin Chem. 1986 Sep;32(9):1746-50.


We assessed the sensitivity, specificity, predictive value of a positive result, and efficiency of tests for total thyroxin, free thyroxin index, free thyroxin, total triiodothyronine, free triiodothyronine index, and free triiodothyronine in serum from 1619 consecutive new patients with suspected thyroid dysfunction. Multivariate discriminant analysis was also used. Free thyroxin index and free thyroxin were clearly the most sensitive indicators of hypothyroidism. In contrast, all of these tests identified hyperthyroidism with similar efficiencies. By stepwise discriminant analysis, the free thyroxin index was the most efficient test for distinguishing between euthyroidism and hyperthyroidism and between euthyroidism and hypothyroidism. The combination of tests for total thyroxin, free thyroxin index, triiodothyronine, and free triiodothyronine was optimal for separating euthyroidism, hyperthyroidism, and hypothyroidism. We conclude that the free thyroxin index, despite the introduction of newer technologies, is still the best thyroid hormone test for screening for thyroid disease.

MeSH terms

  • Adult
  • Diagnosis, Differential
  • Female
  • Humans
  • Hyperthyroidism / diagnosis
  • Hypothyroidism / diagnosis
  • Male
  • Middle Aged
  • Thyroid Diseases / diagnosis*
  • Thyroid Function Tests
  • Thyroid Hormones / blood*
  • Thyroxine / blood
  • Thyroxine-Binding Proteins / analysis
  • Triiodothyronine / blood
  • Triiodothyronine, Reverse / blood


  • Thyroid Hormones
  • Thyroxine-Binding Proteins
  • Triiodothyronine
  • Triiodothyronine, Reverse
  • Thyroxine