Being transfused with the wrong type of blood is incredibly rare, but it has occasionally happened. What does it feel like to have the wrong type of blood coursing through your veins? It feels like being doomed. Literally.
To understand how a transfusion reaction works, we have to look at the many different components in blood. Red blood cells are what give us the A, B, and O blood types, and mismatching them triggers the greatest response, but other cells cause trouble as well. Even correctly matched blood recipients can get fever, chills, and aches if their immune system attacks the white blood cells that came in with their new blood. Platelets in the donor blood also get broken down by the host body, resulting in "purpura," dark purple spots on the skin. The reactions are mild, but doctors don't like to take chances. These days most donor blood is separated into its components before it's deployed. White blood cells are entirely removed — a process called leukodepletion.
The first sign of a transfusion gone wrong is "a feeling of impending doom." This is a legitimate medical symptom, and doctors who regularly work with blood transfusions are told to look for it. Other sign of a mismatched blood type is the usual immune system warning flags — flu-like fever, ache, and chill, as well as a burning sensation at the injection site.
If you're lucky, bad fever and chills are the extent of the reaction. Your immune system will break down the foreign red blood cells, but before doing so, the macrophages in your immune system will engulf them. The red blood cells get filtered out of the blood vessels and broken down in the liver and the spleen. After that there's no more fuss. They're excreted with other waste material.
Things get dangerous when the immune system doesn't wait for the foreign red blood cells to clear the blood vessels before it splits them apart. Hemolysis — the splitting of these cells — spills their contents into the blood vessels. Hemoglobin spills into the plasma of the blood and is excreted in the urine, turning the urine a dark brown color. Red blood cells also contain bilirubin, a component in bile. This usually gets spilled in the liver, which breaks down red blood cells, and excreted. Bilirubin is yellow-brown, and gives your poop its brown color. When the red blood cells is split while still in the bloodstream, the bilirubin turns a person's whole body yellow.
The yellowing skin and brown urine can be managed, but they're signs of a very dangerous situation. The red blood cell debris careening through the blood vessels can set off any number of chain reactions. The debris can activate the complement system, a part of the immune system consisting of cell signaling proteins that activate more cell signaling proteins. The end result of this mass of signals is activation of the membrane attack complex, which rips cells apart. Meanwhile, spilled platelets from the blood cells can trigger an "uncontrollable clotting cascade," causing blood to clot in the veins. This cascade, called an acute hemolytic transfusion reaction, is what can kill people.
Hospitals are careful and mismatches are rare, but they do still happen. In 2013, an 84-year-old woman died after being given the wrong blood type in a transfusion. The hospital's lab had mislabeled the blood. The lab was shut down, and the hospital ordered to get its blood typing done elsewhere.