A nurse is assisting with the care of a client who is receiving a blood transfusion. The nurse should monitor for which of the following findings as an indication the client is having an acute hemolytic reaction?

A. Pulmonary congestion is more commonly associated with fluid overload or circulatory reactions, not acute hemolytic reactions. B. Vomiting can occur with mild allergic reactions or nausea, but it is not a hallmark of an acute hemolytic reaction. C. Urticaria (hives) is typical of an allergic transfusion reaction rather than a hemolytic reaction. D. Low back pain is a classic early sign of an acute hemolytic reaction, often caused by kidney involvement from the rapid destruction of transfused red blood cells.