What is the most common adverse effect of transfusing packed red blood cells?

The most common adverse effect of transfusing packed red blood cells is pyrexia, which refers to the development of fever. This reaction occurs in response to the immune system's response to antigens present in the transfused blood components. When red blood cells are transfused, the recipient's body can recognize these antigens as foreign, which may stimulate an immune response leading to the release of substances that induce fever.

Pyrexia can occur in a significant number of transfusions and, although it is often self-limiting, it is essential for healthcare providers to monitor patients for this reaction. The incidence of pyrexia can vary, but it remains one of the most frequently encountered reactions in clinical practice.

Other adverse effects, while important, are less common in comparison. Allergic reactions, though present, usually manifest as mild symptoms like itching or rash and occur less frequently than pyrexia. Transfusion-related acute lung injury (TRALI) is a serious condition but is relatively rare, as is iron overload, which is a concern with multiple transfusions over time rather than immediate effects related to a single transfusion. Thus, pyrexia stands out as the most common immediate reaction following the transfusion of packed red blood cells.