Commutability Assessment of Materials for Serum Copper Measurement Using the IFCC Difference-in-Bias and the CLSI...

Evidence on the commutability of material for serum copper when assessing multiple material categories and assay pairs remains limited.

We evaluated 21 reference materials for serum copper across four routine colorimetric systems and an inductively coupled plasma mass spectrometry (ICP-MS)-based candidate reference method (System G). The materials included pooled frozen human serum, lyophilized external quality assessment (EQA) materials, aqueous materials, commercial control sera, a certified animal-serum reference material, and manufacturers' calibrators. Commutability was assessed pairwise using the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) difference-in-bias and the CLSI EP30 prediction-interval approaches. The homogeneity and stability of pooled frozen human-serum materials (RM1-RM3) were also evaluated.

Correlations were high across assay pairs, but proportional differences were generally larger in comparisons involving ICP-MS. With the IFCC approach, commutability varied by material type and assay pair; pooled frozen human serum and several serum-based EQA materials showed favorable performance, whereas aqueous materials and some calibrator-related materials more frequently showed assay pair-dependent non-commutability. The CLSI EP30 approach yielded more non-commutable classifications for pairs with ICP-MS than IFCC, but not uniformly across comparisons. Evaluated materials showed better commutability with routine-routine pairs than with pairs including ICP-MS. RM1-RM3 showed low between-vial variation, and bias after storage was lower at -20°C than at 4°C or 20-25°C.

Material characteristics, assay combination, and assessment framework influenced serum copper commutability. Pooled frozen human-serum materials showed favorable commutability, particularly for routine-routine pairs, supporting the use of native serum-like materials in serum copper-commutability studies.