Comparison of Two Different Integration Methods for Quantifying Monoclonal Proteins on Agarose Gel and Capillary Zone Electrophoresis Instruments

Quantifying M-proteins is an important part of diagnosing and monitoring patients with monoclonal gammopathies. Historically, laboratories use one of two methods to accomplish this. The splice method utilizes a perpendicular drop on each side of the M-protein on the electrophoretogram. In contrast, the skim method applies a tangent skimming line connecting the points above the polyclonal background. In this study, we compared the bias between these two methods across two different instruments (Helena SPIFE 3000 and Sebia Capillarys 3) in 118 patients. First, we compared the splice technique on both instruments and observed a significant average bias of 58.3% (slope = 1.437, y-intercept = 0.76, and r = 0.9682). We next compared the splice technique on the SPIFE 3000 to the skim technique on the Capillarys 3 and observed an average bias of only −2.10% (slope = 1.363, y-intercept = −1.98, and r = 0.9716), although there was significant scatter along the line of best fit. Lastly, we compared splice vs. skim on the Capillarys 3 and observed an average bias of −38.2% (slope = 0.947, y-intercept = −2.65, and r = 0.9686). Based on these results, care should be taken when switching instruments or integration techniques to ensure consistent monitoring of patients.