Between-technician Variation upon Estimation of Electrophoresis Peaks of Gammopathy Patients Pedro Medina Escobar, Julie Sottas, Anne Conus, Urs Nydegger, Martin Risch, Lorenz Risch Labormedizinisches Zentrum Dr. Risch, Bern-Liebefeld; Inselspital/Universitätsspital Bern, Switzerland; Zentrallabor, Kantonsspital, Chur 24 As can be seen, tsm produced a mean concentration range (g/l) between 2.5 and 9.0 whereas using pdm, such range extended to as much as from 4.8 to 11.4. On the other hand, using tsm, the CV between-technicians were lower: from 2.6 to 17.4 (tsm) towards 12.0 to 17.2 with the pdm-method. With each of the 5 analyses, the estimated paraprotein concentrations were lower using tsm and revealed less variability among technicians than pdm. Humoral consequences of plasma cell dyscrasias, e.g. monoclonal Gammopathy Disease (mGD) syndromes are monitored using monoclonal peak expression in serum electrophoresis (SPE), free light chain ratio and also, more recently, hevylite™(HLC). Photometric electrophoresis peak and in-between peak (« valley ») profiles are used to estimate the level of abnormal gammaglobulins produced; such approach involves between-technician variation. Introduction The concentration of the M protein at mGD for the clinical follow-up determined by SPE through the integration of the peak monoclonal (PM) can be measured. There are two methods to estimate the level of abnormal gammaglobulins production: the perpendicular drop method (pdm) and the tangent skimming method (tsm) also named valley-to-valley method Figure 1. The configuration can be extracted on Figure 2. Integration of the PM is subject to variation dependent on the technicians experiences. With the present observational study we aimed to show the coefficient of variation (CV) between technicians of these two routine methods. a) b) Figure 1. a) perpendicular drop method (pdm); b) tangent skimming method (tsm) Figure 3. Variation for the 5 selected monoclonal gammopathy profiles and the corresponding coefficients of variation between-technicians. Figure 2. The positioning of a minimum to frame a peak can be made using two approaches: from a lowest point prior to the peak (1) to a lowest point after the peak (2) (valley-to-valley) if the second peak does express a shoulder pattern, an inflexion point is used (skimming); as shown here. For a determination of the inflexion point, a tangent must be laid out at best defined peak and sets the minimum point where the tangent cuts the curve. Discussion For patients suffering from mGD the quantification of protein bands in SPE is used for monitoring and evaluation of response to treatment. As can be seen, it can be difficult to obtain a precise measurement with this technique. With such an large CV for both methods, one should scrutinize the degree of reliance of either way to estimate an extent of gammopathy - in the present study in favour of tsm. Other means to assess for an extent of abnormal protein, calculation of area under the curve, or planimetric approach might help to improve the significance of such technology. It was shown earlier that the pdm procedure overestimates M proteins at concentration below 10 – 20 g/l a drawback which might fade off in higher concentration ranges (1). Priority to use tsm over pdm is mandatory. Using the HLC immunoassays can perhaps improve recognition of the clonality and possibly predict prognosis. The HLC is a very important tool to monitoring the presence of monoclonal component. This is more difficult to identify using SPE. Subjects and Methods We used capillarys 2 Flex-Piercing Sebia™, Alere GmbH. Arbitrary limits using pdm or tsm are subject to validation aleas and are here compared. With 5 patients suffering from mGD we made 5 protein SPE profiles and had them evaluated by 5 different experienced technicians. The results are expressed in g/l paraprotein in serum and the CV is SD/mean. Results Applying tsm/pdm to estimate the level of abnormal gammaglobulin-fraction we found mean concentrations to 2.8/4.8 g/l, 2.5/4.8 g/l, 6.2/8.3 g/l, 5.1/6.8 and 9.0/11.4 g/l Figure 3: profiles 1) to 5). The CV between-technicians (tsm/pdm) were: 9.5/14.0, 17.4/17.2, 6.4/16.9, 2.6/15 and 10.3/12.0 Figure3 (shaded) : CV between technicians. Schild Ch. et al. Reliability of M protein quantification: comparison of two peak integration methods on Capillarys 2. Clin Chem Lab Med 2008;46(6):876–877 Corresponding author: Pedro Medina Escobar, MD E-mail: pedro.medina@risch.ch