Department of Medicine/Endocrinology (Symonds, Kline), Physician Learning Program (Gjata), Department of Clinical Neurosciences (Cooke) and Department of Pathology and Laboratory Medicine (Naugler), Cumming School of Medicine, University of Calgary; Health Services Statistical & Analytic Methods (Rose) and Alberta Precision Laboratories (Guo), Alberta Health Services, Calgary, Alta.
CMAJ. 2020 May 4;192(18):E469-E475. doi: 10.1503/cmaj.191663.
Prescribing of levothyroxine and rates of thyroid function testing may be sensitive to minor changes in the upper limit of the reference range for thyroid-stimulating hormone (TSH) that increase the proportion of abnormal results. We evaluated the population-level change in levothyroxine prescribing and TSH testing after a minor planned decrease in the upper limit of the reference range for TSH in a large urban centre with a single medical laboratory.
Using provincial administrative data, we compared predicted volumes of TSH tests with actual TSH test volumes before and after a planned change in the TSH reference range. We also determined the number of new levothyroxine prescriptions for previously untreated patients and the rate of changes to the prescribed dose for those on previously stable, long-term levothyroxine therapy before and after the change in the TSH reference range.
Before the change in the TSH reference range, actual and predicted monthly volumes of TSH testing followed an identical course. After the change, actual test volumes exceeded predicted test volumes by 7.3% (95% confidence interval [CI] 5.3%-9.3%) or about 3000 to 5000 extra tests per month. The proportion of patients with newly "abnormal" TSH results almost tripled, from 3.3% (95% CI 3.2%-3.4%) to 9.1% (95% CI 9.0%-9.2%). The rate of new levothyroxine prescriptions increased from 3.24 (95% CI 3.15-3.33) per 1000 population in 2013 to 4.06 (95% CI 3.96-4.15) per 1000 population in 2014. Among patients with preexisting stable levothyroxine therapy, there was a significant increase in the number of dose escalations ( < 0.001) and a total increase of 500 new prescriptions per month.
Our findings suggest that clinicians may have responded to mildly elevated TSH results with new or increased levothyroxine prescriptions and more TSH testing. Knowledge translation efforts may be useful to accompany minor changes in reference ranges.
左旋甲状腺素的处方和甲状腺功能检测率可能对促甲状腺激素（TSH）参考范围上限的微小变化敏感，因为这些变化会增加异常结果的比例。我们评估了在一个拥有单一医学实验室的大城市中，TSH 参考范围上限的轻微计划下降后，左旋甲状腺素的处方和 TSH 检测的人群水平变化。
我们使用省级行政数据，比较了 TSH 参考范围变化前后计划变化前后 TSH 测试的预测量与实际 TSH 测试量。我们还确定了新的未接受治疗的患者的左旋甲状腺素处方数量以及在 TSH 参考范围变化前后，对长期稳定接受左旋甲状腺素治疗的患者的处方剂量进行的变化数量。
在 TSH 参考范围发生变化之前，实际和预测的 TSH 测试每月量遵循相同的过程。变化后，实际测试量比预测测试量多 7.3%（95%置信区间 [CI] 5.3%-9.3%），每月增加约 3000 至 5000 次额外测试。新的“异常”TSH 结果的患者比例几乎增加了两倍，从 3.3%（95%置信区间 3.2%-3.4%）增加到 9.1%（95%置信区间 9.0%-9.2%）。新的左旋甲状腺素处方率从 2013 年的每 1000 人 3.24（95%置信区间 3.15-3.33）增加到 2014 年的每 1000 人 4.06（95%置信区间 3.96-4.15）。在长期稳定接受左旋甲状腺素治疗的患者中，剂量升级的数量显著增加（<0.001），每月增加了 500 个新处方。
我们的研究结果表明，临床医生可能会对轻度升高的 TSH 结果做出反应，开出新的或增加的左旋甲状腺素处方，并进行更多的 TSH 检测。知识转化工作可能有助于伴随参考范围的微小变化。
