Final answer:
Cold agglutinins can cause red blood cell agglutination and hemolysis in response to cold temperatures. Hemagglutination can also be caused by certain viruses and bacteria, not just antibodies. The presence of antibodies on RBCs can be detected using the direct Coombs' test, and antibody screening is crucial before blood transfusions to prevent serious immune reactions.
Step-by-step explanation:
When a patient with cold agglutinins experiences a drop in body temperature, it can lead to the agglutination (clumping) of red blood cells in response to the cold. These cold agglutinins are antibodies that react to lower temperatures and can cause hemolysis (destruction of red blood cells) when exposed to cold temperatures. Not only antibodies, but some viruses and bacteria can bind to red blood cells causing hemagglutination, which is the visible clumping of red blood cells. This, too, can have serious health consequences.
The antibodies typically found bound to red blood cells in these conditions are most often IgG. The presence of IgG on red blood cells can be detected using Coombs' reagent in a test such as the direct Coombs' test, which looks for nonagglutinating antibodies and can also detect complement attached to red blood cells. Agglutination may occur under conditions where antibodies such as anti-A or anti-Rh antibodies in the recipient bind to transfused RBCs, leading to a cascade of inflammatory responses and potentially severe reactions such as hypotension, or even shock.
Additionally, an antibody screen test is used to determine the presence of antibodies against RBC antigens that may be less common than ABO or Rh factors. This is especially important for patients who have had multiple pregnancies or transfusions. A cross-match is then performed immediately before a transfusion, where a small aliquot of donor red blood cells are mixed with the patient's serum to check for agglutination, which would indicate incompatibility.