Monday, November 20, 2017
 

A 54-year-old man with an established diagnosis of multiple myeloma was seen for a follow-up visit. He had a history of occasional noncompliance with his therapy. His physical exam was unremarkable, but he did report weight loss and fatigue. Serum protein electrophoresis (SPEP) showed a high abundance of monoclonal paraproteinemia with a strong band in the Γ region. Immunofixation electrophoresis was positive for IgG Γ. Immunoglobulin concentrations were quantitated by immunoturbidimetry, with the following results: IgG <140 mg/dL (RI: 700–1700 mg/dL), IgA <5.0 mg/dL (RI: 70–450 mg/dL), and IgM <21 mg/dL (RI: 50–250 mg/dL). Which of the following laboratory results is unexpected?