What signifies that a blood transfusion should be stopped immediately?

The indicator that signifies a blood transfusion should be stopped immediately is the presence of back pain and dark urine. These symptoms can be suggestive of a hemolytic transfusion reaction, which occurs when the immune system attacks the transfused red blood cells. This type of reaction can lead to the breakdown of red blood cells in the bloodstream, releasing hemoglobin into the circulation, which can then be excreted by the kidneys, resulting in dark urine. Additionally, the occurrence of back pain may be related to kidney involvement or the body's response to the transfusion reaction.

While flu-like symptoms, a fever over 100°F, and chest tightness can signal an adverse reaction to a blood transfusion, they do not represent the immediate threat that back pain and dark urine do. Hemolytic reactions can lead to serious complications if not addressed quickly, making the combination of those specific symptoms critical to halting the transfusion instantly.