Ain K B, Pucino F, Shiver T M, Banks S M
Veterans Administration Medical Center, Lexington, Kentucky.
Thyroid. 1993 Summer;3(2):81-5. doi: 10.1089/thy.1993.3.81.
Patients receiving exogenous levothyroxine are reported to have higher total and free serum thyroxine levels than euthyroid controls. This may be an artifact of the serum collection time. We explored the effect of collection time on serum levels of thyroid hormones in outpatients receiving levothyroxine for replacement therapy (26 patients) or suppression of thyrotropin (25 patients). Blood samples, obtained during regular clinic visits (random samples) and at more than 22 h from ingestion of levothyroxine (trough samples), were assayed for total and free thyroxine, triiodothyronine, and thyrotropin. Four athyreotic patients on levothyroxine therapy had serial blood sampling over 24 h. Compared to corresponding trough samples, random samples had elevated total thyroxine levels in patients receiving replacement (8.1 +/- 1.2%, mean +/- SE, p = 0.0001) and in patients undergoing suppression (8.8 +/- 1.6%, p = 0.0001). Free thyroxine was increased by 12.7 +/- 2.6% (p = 0.0003) and 14.5 +/- 2.3% (p = 0.0001), respectively, compared with trough samples. Thyrotropin levels were 18.9 +/- 6.8% (p = 0.003) lower in patients receiving replacement and triiodothyronine levels showed small or no changes. Time-course analysis showed that free and total thyroxine levels remained significantly elevated above baseline for 9 and 5 h, respectively, after a levothyroxine dose. In conclusion, there is a transient increase in thyroid hormone levels for 9 h after an oral levothyroxine dose. Accurate assessment of thyroid hormone levels in patients receiving levothyroxine therapy should take this into account. This has greatest significance in selecting minimal levothyroxine dosages for suppression of thyrotropin.
据报道，接受外源性左甲状腺素治疗的患者血清总甲状腺素和游离甲状腺素水平高于甲状腺功能正常的对照组。这可能是血清采集时间造成的假象。我们探讨了采集时间对接受左甲状腺素替代治疗（26例患者）或促甲状腺素抑制治疗（25例患者）的门诊患者血清甲状腺激素水平的影响。在定期门诊就诊时采集的血样（随机样本）以及在服用左甲状腺素超过22小时后采集的血样（谷值样本），检测其总甲状腺素、游离甲状腺素、三碘甲状腺原氨酸和促甲状腺素水平。4例接受左甲状腺素治疗的无甲状腺患者在24小时内进行了连续血样采集。与相应的谷值样本相比，接受替代治疗的患者随机样本的总甲状腺素水平升高（8.1±1.2%，平均值±标准误，p = 0.0001），接受抑制治疗的患者也升高（8.8±1.6%，p = 0.0001）。与谷值样本相比，游离甲状腺素分别升高了12.7±2.6%（p = 0.0003）和14.5±2.3%（p = 0.0001）。接受替代治疗的患者促甲状腺素水平降低了18.9±6.8%（p = 0.003），三碘甲状腺原氨酸水平变化较小或无变化。时间进程分析表明，服用左甲状腺素后，游离甲状腺素和总甲状腺素水平分别在9小时和5小时内显著高于基线水平。总之，口服左甲状腺素后甲状腺激素水平会有9小时的短暂升高。在接受左甲状腺素治疗的患者中准确评估甲状腺激素水平应考虑到这一点。这在选择抑制促甲状腺素的最小左甲状腺素剂量时具有最大意义。
