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Thyroid. 2018 Jul;28(7):842-848. doi: 10.1089/thy.2017.0645. Epub 2018 Jun 13.

Does Reverse Triiodothyronine Testing Have Clinical Utility? An Analysis of Practice Variation Based on Order Data from a National Reference Laboratory.

Author information

1 The Center for Effective Medical Testing, The Department of Pathology and ARUP Laboratories, University of Utah Health Sciences Center , Salt Lake City, Utah.
2 Department of Endocrinology, University of Southern California , Los Angeles, California.
3 Department of Endocrinology, Metabolism and Diabetes, University of Colorado , Aurora, Colorado.
4 Department of Family Medicine, Michigan Medicine, Department of Nutritional Sciences, School of Public Health, University of Michigan , Ann Arbor, Michigan.
5 Department of Pathology, University of Utah Health Sciences Center , Salt Lake City, Utah.



Clinical laboratories are under pressure to increase value by improving test utilization. The clinical utility of reverse triiodothyronine (rT3) is controversial. A study was conducted to identify order patterns that might suggest inappropriate utilization of rT3.


All orders for thyroid tests placed over a period of one year at a national reference laboratory were reviewed. Order patterns by client (hospital) and by provider were analyzed. A Pareto analysis was conducted to determine the percentage of orders placed as a function of the percentage of providers. A systematic review of the indexed literature and an informal review of the web were conducted to identify indications for rT3 testing.


There were 402,386 orders for 447,664 thyroid tests, including 91,767 orders for rT3. These orders were placed by 60,733 providers located at 1139 different organizations. Only 20% of providers who ordered thyroid tests placed an order for rT3. Of those who placed an order for rT3, 95% placed two orders or fewer for rT3. One hundred providers (0.1% of the 60,733 providers who placed orders for thyroid tests) accounted for 29.5% of the orders for rT3. Of the 100 providers, 60 with the highest order volumes for rT3 were classified as practitioners of functional medicine. A systematic review of Medline found little evidence to support the high volumes of orders for rT3. A survey of Web sites for functional medicine suggests that rT3 is useful for the diagnosis of rT3 dominance and can be used to direct triiodothyronine replacement therapy.


There is wide practice variation in rT3 testing. A high proportion of tests are ordered by a relatively small proportion of providers. There is little evidence to support high volumes of rT3 testing placed by some practitioners.


practice variation; reverse triiodothyronine; thyroid testing; utilization

[Indexed for MEDLINE]

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