The commutability of thyroid-stimulating hormone international reference preparations plays an important role in...

This study aimed to assess the commutability of thyroid-stimulating hormone (TSH) international reference preparations (IRP) among various assays and to elucidate their role in achieving metrological traceability across systems.

We evaluated the commutability of TSH 3rd IRP 81/565, dissolved in eleven different diluents to achieve two to three different TSH concentrations. The assessment involved 29 serum samples across eight clinical laboratory measurement procedures (CLMP) following the CLSI EP30-A guidelines. Furthermore, 11 different TSH concentrations candidate standard materials prepared from human serum pools (HSPs) were prepared and assigned values from a series of reconstituted IRPs to clarify practical significance of commutable reconstituted IRPs. Two more CLMPs were used to assign values for 11 candidate standard materials using TSH IRP to verify applicability of the diluents.

The TSH IRP demonstrated variable commutability in the eleven diluents, with no single diluent achieving commutability across all assay platforms. Notably, we recorded significant biases of approximately 25.5% and -23.2% when utilizing uncommutable matrices(the TSH IRP were not commutable between CLMPs in these matrices) for value assignments of HSPs via CI 1000 and Cobas 601 assays, respectively. Lastly, Harmonized TSH assigned values ranged from 0.191 μIU/mL to 44.985 μIU/mL, with uncertainties varying between 0.039 μIU/mL and 3.523 μIU/mL using 10 CLMP including 13 methods for 11 different TSH concentration candidate standard materials.

The commutability of TSH IRP is crucial for assigning TSH values in clinical practice. The matrices employed for dissolving IRPs present significant challenges in securing commutability, but their influence is vital for TSH multisystem metrological traceability.