But for the rest of this lecture, I want to focus on
the range of investigations that are used for studying the blood system
and how those are interpreted both in the laboratory and by the clinical teams.
The first and most important investigation in haematology is the blood count.
The blood is taken from the patient and analyzed on a machine.
This is the typical profile that you'll get back from your patient, obviously giving their details
and a range of values there, different cell types and values along the bottom.
Let's go through some of these, talk about the normal values and how we might interpret
some of those abnormalities.
I want to focus particularly on 3 main components within the blood count:(1)the red cell count and the haemoglobin, they go very much together,
(2)the total and individual white cell counts and (3)the platelet count
All of that information will be contained within the blood count and really we have to thank alternative
blood counters for the position we're in in haematology. The whole discipline was transformed when counters
such as the Coulter counter were invented and these can count the characteristics of many millions of cells
very very quickly and provide us with detailed information.
You can see that our machine only got to 16-1/2, but these automated blood counters have really
transformed our understanding of blood disorders. Now I'll show you some examples of how that's done.
The normal red cell count in health is around between 4-6 x 10^12 cells per liter.
That is an awful lot of cells. We have around 5 liters of blood, so you can
certainly get an idea of the vast numbers of red cells within your circulation.
And you will see there, the normal range for men,
between 135-175 and for women, around 11.5-15.5. But I want to make a couple of points here.
One is there is a slight difference in different laboratories as to what the exact normal range is
and it varies slightly with age.
The other thing is, it's quite surprising to have the value that differs in relation to gender.
The men are slightly higher in this case than women. If we measured sodium or potassium,
we won't see a difference there. So why is that? The reason is that the male hormones
are anabolic and they stimulate erythropoiesis and lead to a slight increase in the haemoglobin
concentration as males pass through puberty.
Now oddly enough, the size of a red cell has become very important within haematology and this is because
these automated red cell counters the dimension can provide information on the volume of the red cells
and that's called mean cell volume or the MCV. That's calculated by just counting the number of cells
in a certain volume of blood and dividing it. It is a very odd measurement.
You wouldn't know the volume of a liver cell or a neuron, but in haematology,
we've come to make this very important in our practice and now let me explain why.
Because as you'll see, the size of a red cell is a very useful clue in determining
the cause of diseases particularly anaemia. The volume of a red cell is in this measurement
called femtolitres (fl) and normally it's around 80-95. If the red cells are small, less than 80,
we call it MICROCYTIC. If it's large, over 95 and that is one reasonable cutoff,
we call it MACROCYTIC; and that's very characteristic of different types of anaemia.
White cells are slightly larger cells. Their normal range is much lower than the red cell,
around 4-7x10^9 per litre, they are thousand times less common than red cells.
A decrease in white cells, we call that a LEUCOPENIA; and an increase, LEUCOCYTOSIS.
There are two major types of white cells within the blood: lymphocytes and neutrophils
and we can use those same terms attached to -penia and -cytosis.
Let me explain, you could get a lymphopenia and neutropenia, or lymphocytosis
or actually it is not neutrocytosis, we call it neutrophilia and I don't know why
that slight aberration has derived over the last few years.
PLATELETS. If a patient is complaining of bleeding or bruising, it is important to assess
the platelet count and the platelet function. We normally have around 150-400x10^9 per litre
platelets within our blood. If it's low, we call it a THROMBOCYTOPENIA and that can
be because the patient is not producing enough platelets or there's increased destruction.
If the platelet count is increased, we call that a THROMBOCYTOSIS and that can increase
the risk of blood clots and also paradoxically, bleeding.
Now, haematologists and laboratory scientists love to make blood films and you will see one of the left there.
A little drop of blood is pat on a slide and then smeared out, left to dry and stained.
That means it can then be looked at under the microscope and you will see on the right a really
very beautiful, i think blood film and you will see all the 3 main types of cells on that blood film,
the numerous red cells with its pale centers. The white cells, in fact, there are neutrophils
at the top and a lymphocyte at the bottom and at the back you will see occasional small purple cells,
those are the platelets. You can see straight away why the blood film is such a critical investigation
for many patients with blood diseases. We often want to assess blood clotting.
To do this, blood is taken into a tube with an anticoagulant such as citrate or EDTA
and that means the blood doesn't clot, but what we can then do is add constituents that make the blood
clot and time how long it takes for that clotting to occur. There are two major types of blood clotting tests.
One is called the activated partial thromboplastin time or the APTT, and the other is the prothrombin time
or the PT and these are tests of two slightly different systems within the clotting cascade.
Sometimes looking at the blood within the vascular system is not enough, we need to go to where
the blood is made and examine the bone marrow. Blood is made within the bone marrow and we can
examine the bone marrow by getting access usually to the bone marrow in the pelvis.
The pelvis is very rich in haemopoietic cell production and there are two types of examination that we can do.
We can do an aspirate. This is where we will put a needle into the pelvis
and suck out some liquid bone marrow and look at it under a slide.
We can also take a trephine, that is a histological specimen.
It is a core biopsy that goes into formalin and is sliced up and looked at under the microscope.
They're very different pieces of information as we shall see in a minute.
On the right you will see the areas where we go to take bone marrow - at the back of the pelvis,
the posterior iliac crest and that is where the needle is introduced.
Here we have got examples of a bone marrow aspirate and a bone marrow trephine.
On the left, you will see the bone marrow aspirate. At first sight, it looks similar to a blood smear
but that is actually bone marrow that has been taken out of the pelvis and then drawn along the slide
and if you look next to it, that is what an aspirate looks like when it's stained.
You will see those large areas of fat within the bone marrow and so an aspirate gives you a very nice
ability to look at the detail of the cells within the bone marrow, but it completely disrupts the architecture
Whereas the trephine on the right is a histological specimen, the cells remain untouched
in their natural anatomical distribution. You can see the bone at the top, then you can see
that perhaps over 50% of this bone marrow is fat space and then within that you will see haemopoiesis.
The trephine is a critical test for assessing the cellularity of the bone marrow,
has it got the normal number of cells or are they reduced or increased?
So we usually do both of these tests when a patient needs a bone marrow examination.
Now increasingly genetic analysis is entering haematology as a very important investigation for many patients.
Leukemia derives from malignant white cells and all haematological malignancies are called cancers of course
developed when there is damaged DNA within a cell, and genetic analysis is crucial in the diagnosis
and management of many types of cancer now. There are two major types of genetic analysis
you may wish to do. The first is called a karyotype and thats where you look at all the chromosomes
within an individual cell. You remember that we have 23 pairs of chromosomes.
On the right is a really very beautiful example of a karyotype and the chromosomes have been paired
together and given an individual colour.
But as well as karyotype, more and more these days, we have the ability to look for specific genetic
mutations and that involves sequencing genes within the tumor cells to see where the damage has arisen.
Our cells all have 30,000 different genes, that's what we inherited from our mom and dad
but the mutational analysis is so sophisticated that now we have the capacity to sequence
all of those genes and compare a tumor cell to a normal cell and that will be particularly important
in the new management of malignant diseases.