1. Presented by Liz Crowe MD, PhD and reviewed by Lorraine N. Blagg, MA, MLS(ASCP)SBB

Clinical vignette
A middle-aged adult presents as transfer from an outside hospital with back pain, anemia and renal dysfunction for evaluation of monoclonal gammopathy with elevated serum IgM and serum viscosity (results below). A vertebral biopsy was reviewed and showed involvement by plasma cell neoplasm. The patient denies dizziness, headache, vision change, and epistaxis. Their current complaints are low back pain and hematuria. The apheresis service was consulted to start therapeutic plasma exchange for the indication of hyperviscosity in hypergammaglobulinemia.

Laboratory Studies are as follows:


Serum protein electrophoresis (SPEP) demonstrated an M-spike in the gamma region, which was quantified as >5 g/dL.

Question: What is the most likely explanation for the change in patient's serum IgM results?