Final answer:
The client's symptoms indicate a hemolytic transfusion reaction (HTR) due to an incompatible ABO blood type transfusion, leading to the agglutination and destruction of transfused RBCs.
Step-by-step explanation:
The findings of the client becoming apprehensive and tachycardic, reporting headache and low back pain after initiating a transfusion of packed RBCs indicate a hemolytic transfusion reaction (HTR).
Hemolytic transfusion reactions occur when there is an incompatible ABO blood type transfusion, causing the recipient's antibodies to agglutinate and destroy the transfused RBCs.
The symptoms of a hemolytic transfusion reaction include fever, chills, pruritus (itching), urticaria (hives), dyspnea, hemoglobinuria (hemoglobin in the urine), and hypotension (low blood pressure).