Method comparison for serum protein electrophoretic M‐protein quantification: Agarose gel electrophoresis and capillary zone electrophoresis in canine and feline sera

Background Densitometric quantification of myeloma paraproteins (M‐proteins) is used to monitor secretory myeloma related disorders in humans and dogs. The previous work in dogs used agarose gel electrophoresis (AGE) but did not establish if other methods of serum protein electrophoresis, such as capillary zone electrophoresis (CZE), were comparable. Objectives We aimed to determine if the densitometric quantification of M‐proteins using CZE would yield results comparable to AGE methods. Methods Fifty‐one serum samples from 22 dogs and 18 cats with confirmed monoclonal gammopathies and previously performed AGE were evaluated using CZE on a Sebia Minicap system. Samples were run in duplicate, and their M‐proteins were densitometrically measured using the corrected perpendicular drop method previously described. Human‐based quality control samples were used to determine the inter‐run coefficient of variation (CV). Patient samples were used to calculate the intra‐run CV. Method comparison was performed using simple linear regression, Passing‐Bablok regression, and Bland‐Altman analyses, and Medx evaluations. Results Inter‐run and intra‐run CVs for CZE were 3.71%‐7.65% and 2.89%‐4.74%, respectively. Simple linear regression demonstrated an excellent correlation (r > 0.98). Passing‐Bablok regression was compatible with the presence of proportional bias in the entire population, and Bland‐Altman plots revealed a proportional bias in the feline cases. The Medx evaluation suggested that the two methods did not perform similarly in clinical samples with poor performance at a decision limit of 0.5 gm/dL. Conclusions Capillary zone electrophoresis is an acceptable method for M‐protein densitometric quantification in canine and feline sera but cannot be used interchangeably with AGE‐based evaluations.