Evaluation of the Commutability of Thyroid-Stimulating Hormone Measurements for Proficiency Testing

Background: Commutability refers to the consistency of results from different measurement procedures in regards to a reference material (RM) and representative samples.In this study, we evaluated the commutability of laboratory-prepared pooled sera and commercial quality control materials in the thyroid-stimulating hormone (TSH) proficiency testing program of the Korean Association of External Quality Assessment Service.Methods: Serum TSH from 30 patients was measured in triplicate.Two levels of lab-prepared pooled sera and three levels of commercial materials (Bio-Rad Liquichek Immunoassay Plus) were tested in triplicate at five positions per immunoassay platform (Beckman Coulter UniCel DxI 800, Abbott Alinity i, Roche Cobas e801, Siemens Atellica IM 1600).Commutability was assessed by comparing method differences in patient samples to RMs using the 'International Federation of Clinical Chemistry and Laboratory Medicine' protocol with a desirable bias of 10% based on biological variation. Results:The median TSH level for the 30 patient samples was 2.51-3.07IU/mL, with a coefficient of variation ranging from 1.51% to 4.32%.The median TSH levels of the in-house prepared materials were 0.912-1.01IU/mL for RM2 and 9.10-10.9IU/mL for RM4.The median TSH levels of the commercial materials were 0.391-0.464IU/mL for RM1, 4.39-5.24IU/mL for RM3, and 28.2-35.5 IU/mL for RM5.The in-house prepared materials (RM2, RM4) demonstrated commutability across all six method combinations.Among the commercial materials, RM1 and RM3 showed commutability in four method combinations, while RM5 showed commutability in three method combinations.Conclusions: The evaluation results for the TSH proficiency testing materials showed that the in-house prepared materials had higher commutability than the commercial materials.