Monoclonal Gammopathy of Undetermined Significance Diagnosed by Persistent Anemia Following Living Kidney Transplantation: A Case Report

The prevalence of monoclonal gammopathy of undetermined significance increases with age, and there may be undiagnosed patients among kidney transplant recipients. A 69-year-old woman underwent ABO-incompatible living-donor kidney transplantation. Her renal function improved immediately postoperatively. Her hemoglobin level gradually increased to 10.5 g/dL at 3 months postoperatively but gradually decreased to 7.3 g/dL at 9 months postoperatively. We administered an erythropoiesis-stimulating agent and consulted the Department of Hematology. Bone marrow aspiration revealed that the pathological monoclonal plasma cells constituted 4.6% of bone marrow cells. Immunoelectrophoresis identified serum monoclonal proteins as immunoglobulin G lambda. The patient was diagnosed with monoclonal gammopathy of undetermined significance, and free light-chain measurements were performed regularly. No disease progression was observed. The anemia improved with the administration of an erythropoiesis-stimulating agent. Monoclonal gammopathy of undetermined significance should be explored as a cause of persistent anemia after kidney transplantation.