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The diagnosis and management of subclinical hypothyroidism is assay-dependent- Implications for clinical practice
Tejas Kalaria1, Anna Sanders2, Jonathan Fenn1
1Black Country Pathology Services, The Royal Wolverhampton NHS Trust, Wolverhampton, UK.
Insights
Thyroid assay differences between Roche and Abbott significantly impact subclinical hypothyroidism (SCH) diagnosis. Clinicians must recognize these variations for accurate patient management.
Area of Science:
- Clinical Chemistry
- Endocrinology
- Laboratory Medicine
Background:
- Subclinical hypothyroidism (SCH) diagnosis relies on thyroid-stimulating hormone (TSH) and free thyroxine (fT4) assays.
- Roche and Abbott thyroid assays are widely used in UK clinical laboratories, accounting for approximately 75% of the market.
Purpose of the Study:
- To assess the commutativity of Roche and Abbott thyroid assays.
- To evaluate the impact of assay differences on the diagnosis and management of subclinical hypothyroidism (SCH).
Main Methods:
- Consecutive samples from primary care patients with SCH (raised TSH <10 mIU/L, normal fT4) were analyzed.
- Samples were tested on both Roche and Abbott assays within 24 hours.
- Diagnostic and management discordance were assessed using manufacturer-provided reference ranges.
Main Results:
- Roche assay results for TSH and fT4 were significantly higher than Abbott results (40% ± 15% and 16% ± 7%, respectively; P < .001).
- Only 44% of 93 SCH patients showed concordant results between the two assay methods.
- Significant discrepancies in SCH diagnosis and treatment recommendations were observed between the Roche and Abbott assays.
Conclusions:
- Substantial differences exist between Roche and Abbott thyroid assays, leading to divergent diagnoses and management plans for SCH.
- Clinicians and laboratorians must be aware of between-assay variability and reference range differences to ensure accurate diagnosis and treatment of subclinical hypothyroidism.
Objective:
We assessed the commutativity of Roche and Abbott thyroid assays in the diagnosis and management of subclinical hypothyroidism (SCH). The Roche and Abbott thyroid assays are used by approximately 75% of clinical laboratories in the UK.
Method:
Consecutive samples received from primary care on patients with SCH who had a raised thyroid-stimulating hormone (TSH) <10 mIU/L and a normal free thyroxine (fT4) from two laboratories using either Roche or Abbott thyroid assays were identified over 10 working days. Following identification, samples were analysed at the other site within 24 hours. Diagnostic and management discordance were studied using the relevant manufacturer-provided reference ranges.
Results:
We identified 93 patients with SCH (53 using the Roche assay). Roche TSH and fT4 results were respectively 40% ± 15% and 16% ± 7% higher (P < .001) compared to Abbott results. Of the 93 patients, 41 (44%) were concordant for SCH on both methods. Of the 53 patients with SCH on the Roche assays, 40 (75.5%) had normal thyroid function and 13 (24.5%) had SCH when analysed using the Abbott assays. Of the 40 patients with SCH on the Abbott assays, 28 (70%) had SCH and 12 (30%) had results indicative for levothyroxine replacement when analysed on the Roche assays. Of these 12 patients, four had TSH > 10 mIU/L, five had low fT4 and three had both.
Conclusion:
The diagnosis and management of SCH is strikingly different when using TSH and fT4 assays provided by Abbott Laboratories and Roche Diagnostics. Clinicians and laboratorians should be aware that between-assay differences and variations in reference ranges will directly impact the diagnosis and management of subclinical hypothyroidism.
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