Discrepancies between thyrotropin (TSH) measurement by four sensitive immunometric assays

Area of Science:

• Clinical Chemistry
• Endocrinology
• Assay Development

Background:

• Thyrotropin (TSH) is a key biomarker for thyroid function assessment.
• Accurate TSH measurement is crucial for diagnosing and monitoring thyroid disorders.
• Commercial TSH assays vary in analytical and functional sensitivity, potentially impacting clinical decisions.

Purpose of the Study:

• To compare the performance of four different commercial immunometric thyrotropin (TSH) assays.
• To evaluate the agreement and identify discrepancies between TSH assay measurements.
• To assess assay sensitivity and potential sources of variation.

Main Methods:

• Serum TSH levels were measured in 81 patients with low TSH using four commercial assays: Amerlite, BeriLux, Delfia Ultra, and IMX.
• Analytical and functional assay sensitivities were analyzed for each method.
• Paired t-tests and bias calculations were used to compare assay results.

Main Results:

• Only the Delfia Ultra and Berilux assays showed good agreement (P = 0.7, bias = 0.003 mIU/l).
• Comparisons between other assay pairs revealed significant differences (P < 0.00001, bias > 0.07 mIU/l).
• Despite using the same international standard, discrepancies suggest issues with calibrators or monoclonal antibody specificity.

Conclusions:

• Significant variability exists among commercial TSH assays, impacting measurement accuracy.
• Differences in assay calibrators and monoclonal antibody specificity are likely causes of discrepancies.
• An international collaborative study is recommended to standardize TSH measurements and clarify assay performance differences.