Exp Clin Endocrinol Diabetes 2017; 125(09): 625-633
DOI: 10.1055/s-0043-103018
Article
© Georg Thieme Verlag KG Stuttgart · New York

Monitoring Thyroid Function in Patients on Levothyroxine. Assessment of Conformity to National Guidance and Variability in Practice

Jonathan J Scargill
1   Department of Clinical Biochemistry, Salford Royal Hospital, Salford, UK
,
Mark Livingston
2   Department of Blood Sciences, Walsall Manor Hospital, Walsall, UK
,
David Holland
3   School of Pharmacy, Keele University Benchmarking Service, Keele University, Staffordshire UK
,
Christopher J Duff
4   Department of Clinical Biochemistry, University Hospitals of North Midlands, Stoke-on-Trent, UK
5   Institute of Science & Technology in Medicine, Keele University, Staffordshire, UK
,
Anthony A Fryer
4   Department of Clinical Biochemistry, University Hospitals of North Midlands, Stoke-on-Trent, UK
5   Institute of Science & Technology in Medicine, Keele University, Staffordshire, UK
,
Adrian H Heald
6   The School of Medicine and Manchester Academic Health Sciences Centre, University of Manchester, Manchester, UK
7   Department of Medicine, Leighton Hospital, Crewe, UK
› Author Affiliations
Further Information

Publication History

received 09 October 2016
revised 24 January 2017

accepted 02 February 2017

Publication Date:
13 April 2017 (online)

Abstract

Introduction

With demand for endocrine tests steadily increasing year-on-year, we examined thyroid function test (TFT) frequencies in patients on levothyroxine replacement therapy to assess the effect of initial TFT results and request source on TFT re-testing interval.

Methods

All TFTs performed by the Clinical Biochemistry Departments at the Salford Royal Hospital (2009–2012; 288 263 requests from 139 793 patients) and University Hospital of North Midlands (2011–2014; 579 156 requests from 193 035 patients) were extracted from the laboratory computer systems. Of these, 54 894 tests were on 13 297 patients confirmed to be on levothyroxine therapy in the test cohort (Salford) and 67 298 requests on 11 971 patients in the confirmatory cohort (North Midlands).

Results

In the test cohort, median TFT re-testing interval in the total group was 19.1 weeks (IQR 9.1–37.7 weeks), with clearly defined peaks in TFT re-testing evident at 6 and 12 months and a prominent broad peak at 1–3 months. Median re-test interval was much lower than recommended (52 weeks) for those with normal TFTs at 31.3 weeks (30.6 weeks for the confirmatory cohort). Where thyroid-stimulating hormone (TSH) was elevated and free thyroxine (fT4) was below the reference range, re-test interval was much longer than is recommended (8 weeks) at 13.4–17.6 weeks (7.1–23.4 weeks in the confirmatory cohort), as was the interval when TSH was below and fT4 was above the normal range, at 16.7–25.6 weeks (27.5–31.9 weeks in the confirmatory cohort).

Conclusion

Our findings show that the majority of TFT requests are requested outside recommended intervals and within-practice variability is high. A new approach to ensuring optimum monitoring frequency is required. Direct requesting from the clinical laboratory may provide one such solution.

 
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