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To skim or splice? Comparing the quantification of M-proteins using two peak-integration protocols across multiple
J J Miller1, J Taher2, V Kulasingam3
1Department of Laboratory Medicine & Pathobiology, University of Toronto, Toronto, Ontario, Canada.
Objectives:
M-protein quantification by peak integration in serum protein electrophoresis (SPE) plays a central role in diagnosing, prognosing and monitoring monoclonal gammopathies. The conventional perpendicular drop (PD) integration approach integrates M-spikes from the baseline, which performs acceptably when the M-protein concentration is relatively high compared to the amount of background proteins present. The alternative peak-integration protocol by tangential skim (TS), however, allows for more accurate M-protein estimations by excluding background proteins. Despite some guideline recommendations, TS has been poorly adopted, making an understanding of the differences between the two protocols and their potential impacts paramount when considering a change from PD to TS.
Design & Methods:
We conducted retrospective investigations of the differences in M-protein quantification over large concentration ranges between PD and TS on 3 of the most popular electrophoresis platforms.
Results:
Compared to PD, TS gave consistently lower results; the differences between the two methods increased tremendously and became more sporadic as M-protein concentrations dropped below 15 g/L in all 3 platforms. At < 15 g/L, the average % difference ranged from -81 % to -95 %, while above 15 g/L, the average % difference was only -13 to -31 %. Medical decision point analyses using linear regression predicted statistically significant and platform-dependent differences, which could impact clinical interpretation.
Conclusions:
Careful consideration of the magnitude of concentration changes and the potential impacts on patient classification and management should be made when switching to TS for M-protein quantification.
