Use of thyroid-stimulating hormone tests for identifying primary hypothyroidism in family medicine patients

To assess the use of thyroid-stimulating hormone (TSH) tests for identifying primary hypothyroidism in 2 academic family medicine settings.

Descriptive study involving a retrospective electronic chart review of family medicine patients who underwent TSH testing.

Two academic family practice sites: one site is within a tertiary hospital in Toronto, Ont, and the other is within a community hospital in Newmarket, Ont.

A random sample of 205 adult family medicine patients who had 1 or more TSH tests for identifying potential primary hypothyroidism between July 1, 2009, and September 15, 2013. Exclusion criteria included a previous diagnosis of any thyroid condition or abnormality, as well as pregnancy or recent pregnancy within the year preceding the study period.

The proportion of normal TSH test results and the proportion of TSH tests that did not conform to test-ordering guidelines.

Of the 205 TSH test results, 200 (97.6%, 95% CI 94.4% to 99.2%) showed TSH levels within the normal range. All 5 patients with abnormal TSH test results had TSH levels above the upper reference limits. Nearly one-quarter (22.4%, 95% CI 16.9% to 28.8%) of tests did not conform to test-ordering guidelines. All TSH tests classified as not conforming to test-ordering guidelines showed TSH levels within normal limits. There was a significant difference (P < .001) between the proportions of nonconforming TSH tests at the tertiary site (14.3%, 95% CI 8.2% to 22.5%) and the community site (31.0%, 95% CI 22.1% to 41.0%). Preliminary analyses examining which variables might be associated with abnormal TSH levels showed that only muscle cramps or myalgia (P = .0286) and a history of an autoimmune disorder (P = .0623) met or approached statistical significance.

In this study, the proportion of normal TSH test results in the context of primary hypothyroidism case finding and screening was high, and the overall proportion of TSH tests that did not conform to test-ordering guidelines was relatively high as well. These results highlight a need for more consistent TSH test-ordering guidelines for primary hypothyroidism and perhaps some educational interventions to help curtail the overuse of TSH tests in the family medicine setting.