A client experiences an ABO incompatibility reaction after multiple blood transfusions. Which finding should the nurse report immediately to the healthcare provider (HCP)?

A delayed painful rash with urticaria is more consistent with a mild allergic or delayed hypersensitivity reaction rather than an acute ABO incompatibility reaction. Although this finding should be documented and monitored, it is not immediately life-threatening. ABO incompatibility primarily causes intravascular hemolysis rather than isolated dermatologic manifestations. Choice B reason: Lower back pain and hypotension are hallmark findings of an acute hemolytic transfusion reaction caused by ABO incompatibility. Hemolysis leads to the release of free hemoglobin into circulation, triggering vasodilation, hypotension, renal injury, and severe pain due to renal ischemia. This reaction is a medical emergency that can rapidly progress to shock, disseminated intravascular coagulation, and acute kidney failure, requiring immediate intervention by the healthcare provider. Choice C reason: Acute rhinitis and nasal stuffiness are typically associated with mild allergic transfusion reactions rather than hemolytic reactions. These symptoms do not indicate intravascular hemolysis or cardiovascular compromise and therefore do not require urgent provider notification compared with signs of shock or organ injury. Choice D reason: Arthritic joint changes and chronic pain suggest a long-term inflammatory or autoimmune process rather than an acute transfusion reaction. These findings are unrelated to ABO incompatibility and do not represent an immediate transfusion-related emergency.