'Chemical Hyperthyroidism'

Authors:
  • DSDuncan Salmon
    Duncan Salmon
  • MRMarc Rendell
    Marc Rendell
  • JWJulia Williams
    Julia Williams
  • CSCynthia Smith
    Cynthia Smith
  • DRDavid A. Ross
    David A. Ross
  • JWJohn M. Waud
    John M. Waud
  • JHJohn Eager Howard
    John Eager Howard
Publisher website
Google Scholar
Abstract
• We have observed many patients treated with levothyroxine sodium who have elevated serum thyroxine (T4) levels but appear clinically euthyroid. Such patients generally have normal serum triiodothyronine (T3) values. A retrospective review at The Johns Hopkins Hospital, Baltimore, comparing the correlation of T3and T4values in levothyroxine-treated patients with that in patients not so treated was carried out from 1977 to 1979. Mean free thyroxine index (FTI) value in 104 levothyroxine-treated patients was 4.70 ± 0.2 and mean T3value was 177 ± 9 ng/dL. In a group of 50 hyperthyroid patients, mean FTI value was 7.26 ± 0.5, with a mean T3value of 389 ± 26 ng/dL. In 71 euthyroid patients, mean FTI value was 2.36 ± 0.1, with a T3value of 137 ± 3 ng/dL. Computed ratios of T3to FTI and T3to T4were significantly lower in the group treated with levothyroxine than in either the hyperthyroid or euthyroid nontreated groups. Levothyroxine-treated patients with high T4levels but normal T3levels were clinically euthyroid. Patients not treated with levothyroxine with similarly elevated T4levels had elevated T3levels and were clinically hyperthyroid. It is concluded that lower relative T3levels in levothyroxine-treated patients may explain why these patients appear clinically euthyroid despite elevated T4values. Serum T3determination is the procedure of choice for evaluation of levothyroxine-treated individuals. Furthermore, an elevated FTI value in such an individual does not, in itself, dictate need to reduce dosage. (Arch Intern Med1982;142:571-573)

This publication has 8 references indexed in Scilit: