Question

1. Explain the reasons why a patient's back type wouldn't match the front type.
2. Explain the reason's and situation where you would have an incompatible crossmatch

Answer 1

Ever wondered why some blood typesaren’t ‘compatible’ with others? Or what would happen if you got the wrong blood type during a transfusion? It all comes down to antibodies.

Antibodies are specialised proteins that are produced in response to anything that your immune system might need to fight off, such as bacteria and viruses. Consider them the first ‘identification’ step of the immune system, trying to find anything that doesn’t belong.

Despite the similar name, antibodies are not to be confused with antigens. An antigen is any kind of molecule, such as a protein or a carbohydrate, that can be recognised by the immune system—the antibodies target whichever antigens it identifies as being foreign invaders.

It is important though for the antibodies to not identify antigens that do belong. They’re also produced based on the antigens that are not already present on your red blood cells. For example:

• A type blood has anti-B antibody in the plasma
• B type blood has anti-A antibody in the plasma
• AB has neither A nor B antibody in the plasma
• O has both A and B antibody in the plasma.

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This means that it’s important to get the right donor blood type if you need a transfusion. If an antigen is introduced into your body that isn’t there normally, your system will identify it as an intruder. The immune system will go into attack mode and antibodies will be produced to help fight off the unfamiliar visitors.

For example, if someone with Type O blood (blood with no A or B antigens on the surface of red blood cells) received red blood cells donated from someone with Type B blood (blood containing B antigens), the recipient’s immune system would immediately identify the new blood cells as foreign and seek to destroy them.

Antibodies attack by binding to the foreign antigens on the surface of red blood cells. This ultimately causes those red blood cells to rupture, destroying them entirely. In small amounts, rejected blood can be filtered out by the kidneys, but larger transfusion amounts could cause kidney failure and, potentially, death.
However, if the situation were reversed, and Type O red blood cells were donated to someone with Type B blood, no unfamiliar antigens would be introduced into the recipient’s body, so the blood cells would not be identified as ‘intruders’ by the immune system. This is why Type O red blood cells (more specifically, O negative blood) can be donated to anyone, regardless of blood type, and is known as a ‘universal donor’.

There are three major clinical situations that may lead to difficulty in providing crossmatch compatible blood: Alloantibodies due to previous transfusions or pregnancy. Autoantibodies reacting with common RBC antigens in autoimmune hemolytic anemia (AIHA) and some forms of drug-induced immune hemolytic anemia.

In case of any incompatible major cross-match results, a repeat cross-match with the same donor unit was performed along with two additional group specific donor units. This repeatation was done to rule out any possibility of technical errors (contamination, direct anti-human globulin test [DAT] positive donor unit, mis-grouping, etc.) as well as clerical/transcriptional errors. If the incompatibility persisted on repetitions in any of these 3 units, a further evaluation of the recipient's sample was done in the departmental IH laboratory. The IH laboratory could not routinely perform T/S policy so such an alternative protocol is chosen.