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Biochemical assessment of adequate levothyroxine replacement in primary hypothyroidism differs with different TSH assays: potential clinical implications
  1. Tejas R Kalaria1,
  2. Anna Sanders2,
  3. Clare Ford1,
  4. Harit Buch3,
  5. Jonathan Samuel Fenn1,
  6. Helen L Ashby2,
  7. Pervaz Mohammed2,
  8. Rousseau Mariano Gama1,4
  1. 1 Clinical Biochemistry, Black Country Pathology Services, New Cross Hospital, Royal Wolverhampton Hospitals NHS Trust, Wolverhampton, UK
  2. 2 Clinical Biochemistry, Black Country Pathology Services, Russells Hall Hospital, Royal Wolverhampton Hospitals NHS Trust, Dudley, UK
  3. 3 Endocrinology and Diabetes, Royal Wolverhampton Hospitals NHS Trust, Wolverhampton, UK
  4. 4 School of Medicine and Clinical Practice, University of Wolverhampton, Wolverhampton, UK
  1. Correspondence to Dr Tejas R Kalaria, Clinical Biochemistry, Black Country Pathology Services, New Cross Hospital, Royal Wolverhampton Hospitals NHS Trust, Wolverhampton WV10 0QP, UK; tejaskumar.kalaria{at}


Aim Thyroid stimulating hormone (TSH) assays provided by Abbott Laboratories and Roche Diagnostics are used by approximately 75% of laboratories in the UK. We assessed the potential impact of Abbott and Roche TSH assay differences on the biochemical assessment of levothyroxine replacement in primary hypothyroidism.

Method Samples from 100 consecutive primary care patients (83 women, median age 64 years, IQR 51–73 years) with primary hypothyroidism on adequate levothyroxine based on an Abbott Architect TSH in the reference range were analysed for TSH on Roche cobas within 24 hours. The Abbott and Roche TSH results were compared. Over 1 year, TSH results from patients in primary care from the laboratories with Abbott and Roche methods were compared.

Results The median (IQR) Roche TSH (2.5 (1.3–3.6) mIU/L) was 30%±10% higher (p<0.001) than Abbott TSH (1.9 (1.1–2.6) mIU/L). Although all Abbott TSH results were in the Abbott specific reference range, 14 patients (14%) had Roche TSH results above the Roche specific reference range. In the 1 year gather, Roche TSH (1.9 (1.3–2.9) mIU/L, n=103 932) results were higher (p<0.001) than Abbott TSH (1.5 (1.0–2.2) mIU/L, n=1 10 544) results. The TSH results were above their assay-specific upper reference limit in 10.7% of Roche results and 4.2% of Abbott results.

Conclusion Biochemical assessment of levothyroxine replacement may be dependent on the type of TSH assay. Laboratorians and clinicians should be aware that the lack of harmonisation between TSH methods and their assay-specific reference ranges may potentially lead to different patient management decisions. We suggest lot verification in laboratories should include processes to identify cumulative drift in assay performance.

  • thyroid diseases
  • chemistry
  • clinical
  • endocrinology

Data availability statement

Data are available from the corresponding author on request.

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Data availability statement

Data are available from the corresponding author on request.

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  • Handling editor Tahir S Pillay.

  • Contributors AS and TRK designed the service evaluation under guidance of RMG. JSF, AS and TRK coordinated sample analysis and collected the laboratory and clinical data. TRK analysed data and wrote the first draft of the manuscript. All the authors contributed to data interpretation, critically reviewed the manuscript and approved the final version.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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