‘CHEMICAL HYPERTHYROIDISM’: THE SIGNIFICANCE OF ELEVATED SERUM THYROXINE LEVELS IN l‐THYROXINE TREATED INDIVIDUALS
‘CHEMICAL HYPERTHYROIDISM’: THE SIGNIFICANCE OF ELEVATED SERUM THYROXINE LEVELS IN l‐THYROXINE TREATED INDIVIDUALS
复制标题
“化学性甲状腺功能亢进症”：接受 L-甲状腺素治疗的个体血清甲状腺素水平升高的意义
作者：
M. Rendell;D. Salmon
我们之前报道过，l -甲状腺素治疗的患者可能经常出现血清T4浓度升高，但没有甲状腺功能亢进的临床症状。我们发现这些患者的血清T3浓度正常。本研究探讨了血清T3和T4与1 -甲状腺素剂量的关系。对99例患者进行回顾性分析。血清T4、血清T3树脂摄取（T3R）和T3随l -甲状腺素剂量的增加而增加。T3/T4比值随l -甲状腺素剂量的增加和T4的增加而降低。对这一现象进行了前瞻性分析，从23例患者开始使用1 -甲状腺素，并逐步增加剂量，直到出现甲亢症状或T4水平超过正常范围的上限。再一次，血清T4、T3R和T3随着1 -甲状腺素剂量的增加而逐渐增加。即使是最低剂量的1 -甲状腺素（0.05 mg），与未治疗的个体相比，T3/T4比值也显著下降。T3/T4比值随剂量增加而进一步下降，但相关性较弱。T3/T4比值降低与血清T4相关性更强。23例患者血清T4均超过正常范围上限。除非血清T3也高于正常范围，否则T4升高的个体不会出现甲亢的临床症状。在8名T3水平升高的患者中，有6人表现出甲状腺功能亢进的临床症状。我们的结论是，l -甲状腺素治疗的个体可能表现出T4水平升高，但由于T3水平相对降低，临床甲状腺功能正常。血清T3似乎是l -甲状腺素治疗患者甲状腺功能亢进的最可靠指标。
We have previously reported that l‐thyroxine treated patients may often have elevated serum T4 concentrations and yet show no clinical signs of hyperthyroidism. We found that such patients had normal serum T3 concentrations. The present study explored the relationship between serum T3 and T4 and dosage of l‐thyroxine. Retrospective analysis of 99 patient records was performed. There was an increase of serum T4, serum T3 resin uptake (T3R), and T3 with increasing dose of l‐thyroxine. The T3/T4 ratio decreased with increasing dose of l‐thyroxine and with increasing T4. This phenomenon was analysed prospectively by starting 23 individuals on l‐thyroxine and progressively incrementing the dose until either symptoms of hyperthyroidism developed or T4 levels exceeded the upper unit of the normal range. Once again, there was a progressive increase in serum T4, T3R, and T3 with increasing dose of l‐thyroxine. At even the lowest dose of l‐thyroxine (0.05 mg), there was a marked fall in T3/T4 ratio as compared to untreated individuals. The T3/T4 ratio fell further with increasing dose but with a fairly weak correlation. The decrease in T3/T4 ratio showed a much stronger correlation with serum T4. Of the 23 individuals, all exceeded the upper limit of the normal range of serum T4. No individual with elevated T4 developed clinical signs of hyperthyroidism unless serum T3 was also elevated beyond the normal range. Of eight individuals who reached elevated T3 levels, six demonstrated clinical signs of hyperthyroidism. We conclude that l‐thyroxine treated individuals may show elevated T4 levels and yet be clinically euthyroid as a consequence of a relative decrease in T3 levels. Serum T3 appears to be the most reliable indicator of possible hyperthyroidism in l‐thyroxine treated patients.