BLOOD (aka count dracula's page!!)
So you cut yourself and you bleed - but is that all you know about blood?
Well here's your chance to learn some more about it, what is contains, what
tests you can have with it, the "Dummies Guide to Blood" in other
words. As most of you are aware, my veins are crap (technical term!) after
chemotherapy. They are kinky, fine and deep. Even phlebotomists and theatre
Dr X has been advising again so you know it's all medically correct! =)
If you are at ALL squeamish, please do NOT read on further! You have been
- What is a blood test?
- How is a blood test carried out?
- What do Doctors examine in the blood?
- What blood consists of:
- What your blood test explains:
- FBC (full blood count
- MCV AND MCH
- INR AND APTT RATIO
- SODIUM AND POTASSIUM
- CREATININE, UREA AND URATE
- TOTAL PROTEIN, ALBUMIN, IGG, IGA, IGM B2M
- BILIRUBIN, GGT, AST, ALT, ALKALINE, PHOSPHATE
- FSH AND LH
- Fasting and Non Fasting Tests - what is the difference?
- How is blood produced?
- Do something amazing - give blood!!!
What is a blood test?
Blood tests are sometimes scary for patients, but are a useful diagnostic tool for medical professionals. Blood is made up of several different kinds of cells and other compounds, including various salts and certain proteins.
It is the blood circulating around the body that carries all the nutrients to the cells of your body, and carries away all the waste products, so it has an extremely important role to play.
The liquid portion of the blood is called plasma. When blood clots a mesh of protein (fibrin) is produced from a substance called fibrinogen in the blood, and platelets and red cells stick to this mesh, and this is what forms a 'clot. The remaining liquid (which has 'used up' all its fibrinogen and clotting factors to make a clot) is called serum, which can be used in chemical tests and in tests to find out how the immune system fights diseases.
Medical professionals sometimes take blood samples into lots of different coloured sample tubes. Each of these tubes has different chemicals in them which helps the scientists in the laboratories to do different tests on the blood. For example if you want to measure the ability of the blood to coagulate then it is no good letting the blood clot in the tube before it gets to the lab, and if you want to do measurements on the cells you don't want to have clots in there getting in the way and sticking-up all the cells. So some of these chemicals in the tubes are there to stop the blood from clotting before it can be tested, and some of the chemicals help the blood to clot (if you only need the serum part of the blood), and some of the chemicals help to preserve chemicals in the blood which would 'go off'
quickly without them. There are lots and lots of tests that can be done, which is sometimes why so many different types of tubes are taken.
So that is why SO many tubes of blood are taken ;-)
How is a blood test carried out?
Blood samples for testing can be taken either from a vein (which carries blood to the heart) or from an artery (which takes blood away from the heart).
Apart from and 'arterial blood gas' (ABG) test, most blood tests are taken from a vein, i.e. they test 'venous blood'.
If a small amount of blood is needed (monitoring blood sugar in diabetes
etc) you can make a small prick in the tip of the finger and then squeeze the blood out.
Normally blood tests are taken from a vein near the elbow. A tourniquet is tied around the upper arm to make the vein prominent. It may be a bit tight, but this makes it much easier to take the test. You may also be asked to squeeze your hand to help.
Your arm is then cleaned with spirit and a needle is put into the vein. The needle will be attached either to a low pressure blood test bottle, or to a syringe where the plunger is pulled back to create low pressure. When the necessary amount of blood has been extracted, the needle is removed and a little ball of cotton wool is held over the wound. This should be pressed for one to two minutes before applying a sticking plaster.
Sometimes they use a butterfly needle (this is normally finer) attached to a fine plastic tube which extracts the blood into the tubes using pressure, it sort of 'gulps' it back!
The tubes are under vacuum, hence the name 'vacutainer', and so helps to 'suck' the blood from you to help fill the tube quicker.
Sometimes I have had blood taken from the wrist, this is not normally done in hospitals now as it is quite painful. However if you have difficult veins it could be your only option. I always say if it means getting blood then do it, it's worth a few minutes of pain to get the blood!
Some people are very sensitive to needles and the sight of their own blood and may feel faint when a blood sample is taken. This is not uncommon and can be reduced by sitting or lying down while the sample is taken. If you feel faint or think that you might feel faint, immediately tell the person who is taking blood.
I've had so many tests and have gone from not even looking to now watching as they delve into the arm trying to locate a vein. I've lost count of how many from all areas of my body. In between the knuckles, the wrists, the femoral artery, the legs, the feet, arms you name it and I think I've had a needle in it!
What do doctors examine in the blood?
Blood contains two main elements: the fluid that is called plasma and cells.
There are three kinds of cells: red blood cells, white blood cells and platelets. To get the information they need from the blood, doctors actually do several tests with the blood sample. These include measurements of the levels of the cells or chemicals in the blood. A blood smear is a film of blood placed on a slide to allow doctors to look at the individual cells under a microscope.
what blood consists of:
Your blood is fluid, or plasma. Floating in this plasma, along with some checmicals, are cells:
Red blood cells
One of the most important red blood cell tests is used to find out how
much haemoglobin there is in the blood. Haemoglobin carries oxygen around
your body. This is called the haemoglobin concentration or level.
Another important test, the mean corpuscular volume or MCV test, measures
the size of the red blood cells.
If a person suffers from anaemia their haemoglobin level will always be
less than normal. But the size of the red blood cells depends on the type
of anaemia you have.
A haematocrit test measures the total volume that red blood cells take
up in the blood. In practice, this is done by spinning a test tube of blood
until the red blood cells - the heaviest part of the blood - go to the bottom
of the tube. Then their volume is calculated.
Almost all types of anaemia will cause a low haematocrit (a low red blood
cell volume), as will very severe bleeding. A high haematocrit can occur
if a person is dehydrated from not drinking enough fluid or because they
are losing fluid as happens with diarrhoea, burns and sometimes surgery.
If the red blood cells are pale, it can be a sign of iron deficiency anaemia.
If they have a strange shape, it may be because of sickle cell anaemia or
Doctors also add stains to the blood smear to test the blood for parasites, for example in the case of sleeping sickness or malaria. They may also test your blood for bacteria in the case of sepsis.
White blood cells (WBC)
The doctor counts the total number of white blood cells and works out how
many different types of white blood cells the patient has. This is called
the differential WBC count.
The number of white blood cells may go up and this may be because of a
bacterial infection, bleeding or a burn. More rarely the cause of a raised
white count is due to leukaemia, cancer or malaria.
A person may lose white blood cells because they have autoimmune problems
- this is where the antibodies that should fight diseases attack the body
instead. Other reasons for loss of white blood cells include viral infections.
More rarely, this can be a side effect of certain kinds of medication.
Doctors keep an eye on white blood cells to work out how a disease is changing.
By monitoring the blood count in this way they can alter the patient's treatment
Platelets are very small cells in the blood that clump together at sites of injury to blood vessels. They form the basis of the blood clot that would form if you cut yourself.
Low numbers of platelets can make a person vulnerable to bleeding, sometimes even without injury occurring. Causes of low platelet counts include autoimmune diseases where you produce an antibody to your own platelets, chemotherapy, leukaemia, viral infections and some medicines.
High numbers of platelets make a person more vulnerable to blood clots.
WHAT YOUR BLOOD TEST explains:
fbc (full blood count)
A full blood count (FBC) is one of the most common blood tests done. A blood sample is taken which is prevented from clotting by using a preservative in the blood bottle. The sample is put into a machine which automatically:
- counts the number of red cells, white cells, and platelets per ml of blood.
- measures the size of the red blood cells and calculates their average (mean) size.
- calculates the proportion of blood made up from red blood cells (the haematocrit).
- measures the amount of haemoglobin in the red blood cells.
Of course, this may also be done manually by the 'people in white coats in the labs'.
The units that the lab uses to measure the test in - the different types of cell are also counted - this may be done by a machine or by looking down the microscope (manual count).
HB (Haemoglobin), RBC (Red cell count) and PCV (packed vell volume) are all slightly different ways of seeing if you are anaemic (i.e. if you have enough of those little red cells). If this is low the reasons should be checked out - it may be that a blood transfusion may help.
mcv and mch
MCV (Mean cell volume) and MCH (mean cell haeoglobin) are measures of the average size and density of the red cells. If you are lacking in iron, for example, the cells may be small and pale.
A lab control value which is useful to the lab people, but is not important otherwise.
Chemo can drop your platelet count although not usually to levels which could cause bleeding.
inr and aptt ratio
These are clotting tests. The INR (International Normalised Ratio) and others are often expressed as a ratio of your clotting time against a 'control' (normal) plasma.
(Erythrocyte Sedimentation rate) is a rather vague test of general inflammation or unwellness. This is tested not only with a cancer diagnosis but also many other illnesses. John has his checked with his Rheumatoid Arthritis because it is a good measure of inflammation.
SODIUM AND POTASSIUM
Salts in the body - these tend to be altered by general conditions in the body as well as going on in the liver and kidneys
Levels can help indicate how alkaline or how acidic your blood is.
CREATININE, UREA AND URATE
Shows how your kidneys are behaving.
An enzyme in your pancreas which will rise if damage is occuring, for example in pancreatitis.
Your blood sugar levels - if you are diabetic or take steroids they will keep an eye on this.
Thyroid Gland Function, means 'thyroid stimulating hormone'.
A mineral in your bones. Measured directly then 'adjusted' to take account of the albumin levels.
A general marker of inflammation, similar to ESR but more specific.
total protein, albumin, igg, iga, igm, b2m
The total amount of protein is measured in the blood. Your albumin could be low if you've not been eating well or the liver is damaged. The IGS are part of your immunity. They could be raised (or lowered) as a part of the immune damage with the Lymphoma. B2M is a protein sometimes used to assess or follow Lymphoma.
bilirubin, ggt, ast, alt, alkaline phosphate
Liver enzymes can be raised because of disease, treatment or compllications.
If the bilirubin is raised you could have a yellow tinge to your skin (I was like Marge Simpson apparently - minus the blue hair of course - as I had
none!) or whites of yours eyes.
An enzyme (lactate dehydrogenase) that can be used to assess Lymphoma and sometimes follow progress, but has other uses to.
A heart and muscle enzyme.
fsh and lh
Sex hormones - follicle stimulating hormone and lutinising hormone, these might be assessed if the menopause looks like it may have started.
FASTING TESTS AND NON FASTING TESTS
When we eat a meal our blood sugar will rise afterwards as the meal is digested and the sugars from the meal enter the bloodstream to be used by the body, as time passes the blood sugar level should return back to normal levels. Patients who have diabetes generally have a high blood sugar. So how do doctors tell if a person has a high glucose level because they have recently eaten a meal, or because they are diabetic??
Well, a "fasting glucose" test means that the blood sample is taken at least 8hrs after your last meal or intake of food. If you have a high blood glucose level for a "fasting" sample, then it indicates the patient may have diabetes, whereas a high value for a non-fasting sample might be normal if you have just eaten, or it might not be... so it makes interpretation of the result more difficult... which is why patients will sometimes be asked not to eat anything for 8 hrs prior to a blood test. It makes it easier for their doctor to interpret the results.
How is Blood Produced?
Blood cells are produced in the bone marrow, a jellylike substance inside the bones that is composed of, among other things, fat, blood, and special cells that turn into the various kinds of blood cells. In children, the marrow of most of the bones produces blood. But in adults, only the marrow of certain bones -- the spine, ribs, pelvis, and some others -- continues to make blood. Bone marrow that actively produces blood cells is called red marrow, and bone marrow that no longer produces blood cells is called yellow marrow.
All blood cells come from the same kind of stem cell, which has the potential to turn into any kind of blood cell. These stem cells are called pluripotential hematopoietic stem cells.
As the blood cells develop from the stem cells in the marrow, they seep into the blood that passes through the bones and on into the bloodstream. The different kinds of blood cells have different "life spans" - red blood cells last about 120 days in the bloodstream; platelets about 10 days; and the various kinds of white blood cells can last anywhere from days to years.
The body has a feedback system that tells it when to make new red blood cells. If bodily oxygen levels are low (as they would be if there are too few red blood cells circulating), the kidneys produce a hormone called erythropoietin (Epo), which stimulates the stem cells in the marrow to produce more red blood cells. This is essentially how the body regulates the number of cells and maintains a balance, producing enough for its requirements, but not too many. Some athletes inject Epo to stimulate their marrows to produce more red cells, and hence they are able to transport more oxygen to their muscles, and hence able to train harder, run faster, etc.
This is one of the dangerous ways in which humans can interfere with their own physiology in the name of sport.
If you have any questions on blood or blood tests please email
do something amazing - give blood!!
Now that I am no longer scared of needles and blood tests they tell me
I can't give blood because:
2. I've had chemotherapy
3. I've had blood transfusions (when I had my ERCP and they cut me internally
in hospital and I had a scary few weeks trying to get back to the real world...!)
Please check out the following excellent site for information about taking
and giving blood:
National Blood Service
Billy Blood Drop and Betty Bone Marrow