In this lecture, I would like to introduce
the principles of blood transfusion.
We'll see that blood transfusion accomplishes the safe
transfer of blood products from one person into another.
We'll see that there are strict criteria about
who can donate blood and this is done
in order to protect the donor and the recipient.
We'll also see how because of genetic differences
between individuals, blood products need to be matched
so that they are given to the right person.
We'll see that there are potential complications
of blood transfusion, but, fortunately,
these are really mostly very rare events these days.
Transmission of infection has been a particular
concern, but that's now really very well controlled.
Now transfusion involves the transfer of blood between
individuals and it's really fascinating that blood
really was the first tissue that was transferred
between different individuals many decades ago.
We tend to think of blood transfusion,
of transfusion of red cells, a pack of red cells,
but there are many types of blood products
that are now available.
And I will address those during this lecture.
A key theme about blood transfusion is to decrease
the potential risk of this procedure at
all stages of the process. Let us just think about the
variety of blood products that are available.
I'm sure many of you are blood donors and when
you give blood, you typically give around
400 to 440 ml of blood into an anticoagulated bag,
something similar to what is seen on the right.
Now most blood these days is leucodepleted. What does
that mean? leucodeplete (leuco - white, deplete - take out)
"take out the white cell"; the blood is essentially
filtered to take out the white cells in the donation.
Why do you want to do that? Sometimes white cells can
provoke allergic reactions when they're given to a patient.
Also there are some rare but important infectious
diseases that are present within white cells and so
taking out the white cells at this stage can
reduce that risk.
Now actually when you give a blood donation
potentially something like on the right,
it's not given directly to a patient. The blood is quite
significantly processed into various fractions.
The blood is centrifuged after donation and the red
cells at the bottom are concentrated in order
to be used for red cell transfusion. The plasma
can be taken off to make fresh frozen plasma
and I'll talk about the uses of that later on.
Platelets are very important and they can be given
to patients with thrombocytopenia.
They are taken from the buffy coat,a layer of white cells
and platelets that is visible after centrifugation.
You can already see how when you donate a unit of blood,
how we can make very useful
different fractions from that.
Here are some features of donating blood.
It's preferable if donors give their blood on a voluntary
basis so they are not given payment, so called altruism.
Why is that? Well essentially if people are being paid
to give blood, there might just be a suggestion that they
might perhaps lower the criteria for why they give blood.
People are more motivated if they're not being paid
and so many countries do organize blood donation
systems on this basis.
Of course, not everybody is allowed to give blood.
These so-called exclusion criteria protect the donor
so that the donor does not come to any harm by giving
one bag of blood, but also protect the patient.
Age is one, mustn't be too young or too old and of
course if the donor is anaemic, they mustn't give blood.
In order to protect the patient there are additional
factors, there are many of these.
For instance, if the donor has a chronic illness or
malignant disease; if they've had things such as a
recent tattoo or they have a history of
intravenous drug use
that's about the risk of potential viral infections
such as hepatitis C.
Minor things even if they've had a recent live
vaccination just so that that infection
is not spread perhaps to the patient, the risk
is absolutely minimal, but you can see already
how strict the criteria are for blood donation.
Now when blood is given by donor, it is screened.
Obviously infections such as hepatitis, HIV and syphilis,
we must look for those within the blood donation.
There's two main ways to do this.
The first is by looking for the presence of antibodies
in the blood against these infectious agents.
That will show that the patient has that infection
for sometime at least weeks and that gives
time for the antibody to develop.
But also particularly with hepatitis and HIV,
we can look for the antigen, the presence of the
infectious agent, the virus itself by using PCR,
Polymerase Chain Reaction.
Why do we bother to do that? Why not simply
do an antibody screen?
Well, sometimes if a patient has a recent infection
that haven't had time to develop an antibody
and in the so-called window period recent infection
and blood donation during that period,
there is the chance that infection can be
transmitted before an antibody is produced.
But if we screen for the antigen, then we
can get around this concern.
You see on the right there, a list of the type
of tests that are done on a unit of donated blood
The ABO group and Rhesus group I'll talk about
most of those in detail in a second -
red cell antibody screen and screening for
the infections that I have just described.
Now , let me introduce a major concept in blood
transfusion, very important clinical idea
and that is of course, there are genetic
differences between all individuals
and that means that when we give a blood product
from one person to another, we've got to crossmatch it
to make sure that we are giving a safe unit of blood.
Let me just word down those statements on the left.
So genetic differences between individuals mean
the proteins on blood cells can be slightly different
between the donor and recipient.
You are not surprised by that, we all have 30,000 genes.
There are lots of allelic changes in those genes and so
sometimes proteins on white cells and red cells
are slightly different and that doesn't really matter
except when the immune system becomes involved
because these differences can be recognized by the
immune system and leads the production of antibodies
against that protein, and it's these antibodies,
that can cause the problems.
Now as I also discussed
when we talked about ABO in detail,
remarkably, sometimes we have these antibodies in our
body against other people's red cells
even when we have not even been stimulated or
immunized by those red cells.
The so-called natural antibodies just happened to be
there. We don't really understand why.
The classic example is the ABO system, and because
of this when we give a blood product,
we must test that the blood that's given
does not react with antibodies in the patient
and that is shown in the cartoon on the right.
Let me take you through that in a little more detail.
So here we are.
Starting on the left, those red cells there
are donated red cells that we want to
give to the patient, but it may be that
the patient has antibodies against those red cells and
you can see the antibodies around those red cells.
So we can put them together - the donor red cells
and the patient's serum and give them chance to mix
and then as you'll see in the middle,
we can wash off the patient's serum
so that we're left with the donor red
cells and you'll see that in this case,
some of the antibodies from the patient have indeed stuck
to those donor red cell and that's a potential problem.
Now actually you can see, how do we detect these?
The red cells are just still individually floating around.
How do we detect that those antibodies are present?
Well, cleverly we can use something called
the Coomb's Reagent on the right.
This is an antibody that is made in another animal
perhaps like a sheep.
It's anti-human immunoglobulin and if you'll see
on the top right of that,
this antibody is now crosslinking these different
red cells through that antibody.
Its two layers are so-called sandwich assay of
antibodies, and this Coomb's test leads
to the agglutination of the red cells; they clump
together and they visibly show us
that those antibodies are coating the donor red cells.
That's a positive crossmatch that can't be given.
Now the other situation in which antibodies
can be important is that they develop
after a blood transfusion has been given.
This is perhaps less of a concern.
It doesn't cause immediate clinical problems,
but problems that are seen a little bit later on.
The most important example of this
is the rhesus system
and I'll explain the rhesus antigen and
the proteins decoded from that in some detail.
Now why have I shown you that blood film on the right?
That is actually from a newborn baby and you will see
that there are a lot of very primitive red cell
precursors, so called erythroblasts in the blood.
That's unusual. You wouldn't normally
see those certainly in adult.
You occasionally see a few in a newborn baby,
but here there is a lot.
The reason that this baby is being damaged due to
Hemolytic disease of the newborn.
The mother has made antibodies to the rhesus antigen
and they have crossed into the placenta
and so the mismatch between the mother and the baby
is one example of what can happen
when an antibody is made between different individuals.
I will show you more about the clinical importance
of the rhesus antigen in subsequent slides.