An educational case of multiple myeloma in a patient undergoing peritoneal dialysis: The significance of β2-microgloblin

Abstract Background β2-microglobulin (β2-MG) is recognized as a surrogate marker for putative middle-molecule uremic toxins. Its clearance by peritoneal dialysis (PD) is limited but increases significantly when hemodialysis (HD) is added. In Japan, combined PD and HD therapy is frequently introduced when patients undergoing PD experience a decline in residual renal function. However, even with combined therapy, persistently elevated serum β2-MG levels often lead to a transition to thrice-weekly HD. This report describes a case in which elevated β2-MG levels were attributed to overproduction rather than insufficient solute removal in a patient receiving combined PD and HD therapy. Case presentation The patient, a 76-year-old woman with end-stage renal disease due to immunoglobulin (Ig)A nephropathy, initiated PD 12 years prior and started weekly HD 2 years prior, following a reduction in residual renal function. Despite the addition of HD, serum β2-MG levels remained elevated; however, peritoneal function was preserved, and PD was continued. The patient later experienced a spontaneous fracture of the right distal radius, leading to a diagnosis of multiple myeloma, which was identified as the underlying cause of the elevated β2-MG. Following initiation of chemotherapy, β2-MG levels declined markedly. Conclusions In prevalent patients with PD, serum β2-MG alone has limited prognostic value. This case highlights the need for a comprehensive assessment when interpreting elevated β2-MG levels and supports individualized treatment decisions rather than reliance on a single biomarker.