ArticleCMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne2020
Levothyroxine prescribing and laboratory test use after a minor change in reference range for thyroid-stimulating hormone.
Article in CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne, 2020. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 1 paper.
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- What happens when laboratory reference ranges change?CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne · 2020Article
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7 authors at 1 institution in 1 country.
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No grant is acknowledged in the PubMed record.
Abstract
backgroundPrescribing 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.
methodsUsing 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.
resultsBefore 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 (
interpretationOur 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.
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