L BERNASCONI¹, E MUNDWILER¹, M HEIZMANN², M BARGETZI², N CANTONI², AR HUBER<sup>1

1</sup>Institute of Laboratory Medicine, Kantonsspital Aarau, Switzerland, ²Division of Hematology, University Clinic for Medicine, Kantonsspital Aarau, Switzerland

Serological follow-up of patients undergoing autologous stem-cell transplantation (ASCT) is currently based on the measurement of the monoclonal component using serum protein electrophoresis (SPE) and immunofixation electrophoresis (IFE). Hevylite (HLC) is a new assay allowing the quantification of intact heavy/light-bounded chains of a given immunoglobulin. Our study aimed to compare the sensitivity of conventional techniques (SPE, IFE) to nephelometric/turbidimetric assays (HLC and free light chain assay, FLC) in detecting serological relapse in patients after ASCT. Methods: consecutive routine sera submitted to our laboratory during follow-up of 21 myeloma patients (16 IgG, 1 IgM, 4 IgA) after ASCT were examined with SPE, IFE, HLC, FLC. 15 patients (4 IgA and 11 IgG) relapsed. Time to serological relapse was determined using conventional methods (SPE, IFE) and compared to relapse indicated by HLC and FLC. Results: in 6 patients (2 IgA and 4 IgG) HLC measurements indicated serological relapse earlier than conventional techniques (mean: 4 months earlier). In two of these cases FLC indicated a serological relapse earlier than HLC. In three cases (1 IgA and 2 IgG) SPE/IFE detected the reappearance of the original monoclonal component earlier (mean: 3 months) than HLC. In all remaining cases serological relapse was detected simultaneously by conventional and nephelometric/turbidimetric techniques. Conclusion: HLC and FLC are valuable complementary methods to conventional techniques (IFE, SPE) and improve sensitivity in the identification of serological relapse during follow-up of patients after ASCT.