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Significant variations of thyroid testing in the US argue for improved standardization of practice patterns

CTFP Volume 11 Issue 3

Thyroid problems are common and the symptoms are often very nonspecific. This is especially true with hypothyroidism. There are many different tests available to evaluate the function of the thyroid gland. However, many tests are over utilized and/or may not be appropriate for the type of thyroid problem suspected. Over the past few decades, there has been a steady increase in the number of thyroid tests ordered and the estimated cost for the most commonly ordered tests (TSH and free T4) totals $1.6 billion per year.

The objectives of this study were to compare patterns of thyroid testing ordered between different institutions, to assess the appropriateness of such testing, and to evaluate whether laboratory utilization protocols showed improvements in thyroid testing.

Lin DC et al and the Thyroid Benchmarking Group. Multicenter Benchmark Study Reveals Significant Variation in Thyroid Testing in the United States. Thyroid 2017;27:1232-45.

This study was done with data obtained from 82 laboratories associated with 24 unique US healthcare organizations, of which 13 were academic medical centers. The sites were selected from a voluntary web-based survey. The volume of serum thyroid tests over the 2015 calendar year was determined for the following tests: TSH, free T4, total T4, free T3, Total T3, T3 uptake and reverse T3. Then, that volume was standardized against the frequency of complete blood count (CBC) testing, probably the most common blood test ordered. The prevalence of CBC testing was also used to determine the total testing volume of each laboratory so that comparisons regarding overall volume across health care centers could be done. Researchers divided data by inpatient vs. outpatient patient settings. The investigators also collected data related to health care utilization management initiatives at each center.

The results showed that across the 82 laboratories, there was a higher proportion of TSH testing among outpatients than inpatients. Based on median values, sites ordered 14 Free T4, three total T4, four free T3, two total T3, 0.1 rT3 and 0.1 T3 uptake for every 100 TSH orders. Tests for free T4 were nine times as common as those for Total T4, but free T3 and Total T3 were more evenly split. Comparing between sites, there were marked variations in whether an initial screening TSH was obtained and also in the order of tests ordered following an initial TSH. One of the most variable ordering behaviors for thyroid testing was whether a rT3 level was obtained following an initial TSH. This happened even though there were general laboratory testing guidelines available to providers at 71% of the sites. At 38 % of the sites, some tests were restricted to specialists, but only 21% of centers had guidelines for when it is appropriate to obtain thyroid testing.

This study shows that there is significant practice variation in thyroid testing and suggests a need for better guidance in test selection to improve patient care and reduce testing costs. Although the study has limitations, including the lack of clinical information that would support a particular test over another, its strength is its relatively broad sample size which makes it likely to reflect practice patterns across the entire United States.

— Jessie Block-Galarza, MD

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Thyroid Function Tests:


Thyroxine (T4): the major hormone produced by the thyroid gland. T4 gets converted to the active hormone T3 in various tissues in the body.

Triiodothyronine (T3): the active thyroid hormone, usually produced from thyroxine.

TSH: thyroid stimulating hormone — produced by the pituitary gland that regulates thyroid function; also the best screening test to determine if the thyroid is functioning normally.