Paroxysmal Cold Hemoglobinuria Associated With Monoclonal B-Cell Lymphocytosis in an Elderly Patient: A Report of a Rare Case.

We report the case of an 86-year-old male with chronic anemia who presented with indirect hyperbilirubinemia, undetectable haptoglobin, and reticulocytosis. The peripheral smear showed no schistocytes. The cold-agglutinin titer was mildly positive, and the Donath-Landsteiner antibody test was positive. Bone marrow biopsy revealed a small CD5⁺ B-cell clone consistent with monoclonal B-cell lymphocytosis (MBL). The patient was diagnosed with paroxysmal cold hemoglobinuria (PCH) associated with MBL and treated with rituximab, achieving clinical stability without transfusion requirement. This case illustrates a rare coexistence of PCH and MBL in an elderly patient and emphasizes the importance of comprehensive hematologic evaluation for unexplained chronic hemolysis.