INTRODUCTION: For 50 years, clinical laboratories relied on protein electrophoresis and immunofixation (IFX) for detecting and isotyping M-proteins. While IFX is easy to implement in a clinical laboratory, it suffers from low sensitivity and lack of specificity (i.e. distinguish between minor mass-dissimilar M-proteins). We recently developed an isotype-specific nanobody enrichment-based MALDI-TOF method, termed Mass-Fix, for isotyping M-protein. Mass-Fix, while being more sensitive and specific, is more labor intensive to implement in a clinical laboratory when compared to IFX.
METHOD: We automated Mass-Fix for routine clinical laboratory use. Automation uses Hamilton liquid handler to process 64 samples in a batch. Processed samples are spotted on a MALDI target plate using Mosquito HTS. Spotted plates are analyzed with Bruker MALDI-TOF. Patient spectra are automatically captured and presented for review. Entire automation is driven by custom developed software that seamlessly interacts with all instruments and laboratory information system. Software minimizes user interactions with platform and maintains positive patient ID throughout the process. This set up is highly efficient (256 samples/person/shift) and scalable (multiple instruments managed by one software install).
RESULTS: 182 serum samples were analyzed with Mass-Fix, serum PEP (SPEP) and IFX: 84 were SPEP and IFX positive, 70 were SPEP negative and IFX positive and 28 were negative by both SPEP and IFX. Mass-Fix detected M-proteins in 100% of SPEP and IFX positive samples and 99% of IFX positive samples. In SPEP and IFX negative samples, Mass-Fix identified M-protein in 2 samples. Mass-Fix also analyzed 112 IgG/IgA multiple myeloma serum samples that were characterized by SPEP, serum IFX and Hevylite assay. Mass-Fix detected M-spike in 96% of samples when compared to 90%, 75% and 70% for IFE, Hevylite and SPEP.
Mass-Fix’s ability to isotype M-proteins was tested with 152 serum samples that were SPEP and IFX positive. We observed 95% concordance in isotyping between Mass-Fix and IFX. In 6 samples with disagreement, both techniques agreed on the major M-protein’s isotype, but Mass-Fix detected additional smaller M-proteins. Quantification ability of Mass-Fix was tested against SPEP. Mass-Fix has a lower LOD of 0.01g/dL compared to current methods.
Serum Mass-Fix was implemented for routine clinical use at Mayo Clinic and analyzed 8001 patients with SPEP abnormality. We detected no M-protein in 5304, monoclonal IgG in 1695, monoclonal IgA in 398, small IgM in 167, Bence Jones proteins in 164, monoclonal IgM in 152, biclonal gammopathy in 109, and multiple small clones in 12 patients. LCs mass-consistent with daratumumab and elotuzumab were detected in 219 and 23 patients, respectively. We detected glycosylated LC (AL amyloidosis risk marker) in 116 patients.
CONCLUSION: Automated Mass-Fix is an effective platform to replace IFX for serum M-protein detection and isotyping.