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But these slight differences, which don’t affect the efficiency or the working of the cells at all,
are not on their own sufficient to cause trouble on transfusion. The problem arises because, after a
few months outside the womb, the blood serum begins to build up antibodies to the opposite
version of the molecule on their own cells. People in group A build up anti-B antibodies in their
serum. Again, this does not interfere with normal everyday life. People never make antibodies to
their own blood cells, so people in group A don’t make anti-A antibodies, only anti-B. Since
people with blood group AB have both versions on their red cells, they make neither anti-A nor
anti-B antibodies while, for the same reason, people in group O, whose cells have neither A nor B,
are free to make both anti-A and anti-B antibodies and they do.
The potentially fatal coagulation reaction occurs when the molecule meets its antibody. They
stick to each other like glue and, what is worse, bind all the red cells into a sticky clump, the cause
of all the trouble in mismatched transfusions. That’s why no one makes antibodies against their own
cells. They would coagulate their own red blood cells and die.
Under normal circumstances blood cells never encounter their own antibodies, but transfusion
opens up that possibility. Transfuse a group A patient with blood from a group B donor and the
antibodies will play havoc. Two things happen. The group B cells from the donor are coagulated
by the anti-B in the patient’s serum and the anti-A in the donor’s serum clumps the patient’s own
cells. Group O blood is really bad news because its serum contains both anti-A and anti-B which
will attach the cells of any other blood group. However, as good methods were developed to
separate the donor’s cells from the liquid serum, things got a bit easier. Group O cells, separated
then rinsed free of antibody-containing serum, can be transfused into any patient, and if red cells
are all you need that’s fine. Group O is the universal red-cell donor, as long as you wash them
thoroughly first to remove the serum antibodies. If you need serum, not cells, then a transfusion of
AB serum, which is free of antibodies, will suit any patient whatever their blood group.
Once all this was understood, it was easy to see why so many transfusions failed. Without
knowing in advance the blood group of donor and patient, blood transfusion was a really hit-andmiss
affair. At least that was the case in Europe. Stories that the Incas of Peru had been
successfully performing a form of blood transfusion without any adverse reactions were initially
dismissed as nonsense. However, when it was discovered that practically all native South
Americans were in blood group O, it no longer sounded so incredible. If Inca donor and Inca
recipient were both in group O, as most were, then trouble-free transfusions are exactly what
would be expected.
Before the First World War, blood transfusions were a personal business. Willing friends and
relatives of the patient would be tested to find someone in a compatible blood group. The donor
would then come to a hospital, usually the operating theatre if surgery was the reason for the
transfusion, and be bled right next to the patient, who then immediately received the fresh blood.
The huge increase of blood transfusions needed to treat the battlefield casualties of the First World
War led directly to the setting up of blood banks and the recruitment of donors along modern lines.
Under the right conditions it was found that blood could be stored for several days without losing
condition and there was no need to transfuse casualties immediately with absolutely fresh blood.
Volunteer donors were bled at remote sites and the blood was despatched to the field hospitals
at the Front to be matched and used as required. This soon became a large-scale activity and with it
came the necessity for accurate records. Each army had its blood bank and they soon began to