 Your
blood tests
by Dr Paul Revell
| Dr Paul Revell, the Lymphoma
Association’s Medical Adviser, is a Consultant Haematologist at Staffordshire General
Hospital and Co-ordinator of Cancer Services for the Mid Staffordshire General Hospitals
Trust. He is particularly interested in
helping patients to understand their illness and treatment. |
Introduction
It is worth bearing in mind that there is a big difference between having a blood
sample taken and a blood test. When you have a sample or samples taken this may be for one
single test or for a whole battery of different tests on the same sample.
There are, in fact, hundreds of possibilities but I will only deal with the commoner
ones here. Not all tests will be repeated on each occasion - the relevant ones will be
requested by your doctor.
What can you measure
in the blood?
Broadly, you can measure levels of chemicals and also count and measure the cells.
Occasionally a ‘blood group’ test will be needed (if you need a transfusion - so
the correct donor blood can be selected for you).
‘A blood culture’ can be done if you are unwell to see if any bugs have made
it into your circulation (and if any are grown in the test, the result can help in
choosing the right antibiotic).
Chemicals and cells in
the blood
Your blood is fluid, or plasma (see later). Floating in this plasma, along with some
chemicals, are cells ( see figure 3 ) :
- red cells which carry oxygen around the body,
- white cells - which fight infection and
- platelets which help clotting.
All these cells are made in the bone marrow and, when they are worn out, the bits are
recycled (mostly in the spleen or liver). The red cells and platelets tend to stay in
the circulation whereas the white cells creep about everywhere - including the organs of
the body and the lymph glands.
The numbers of all these cells can be measured and also their sizes and types -
see figure
1.
The factors which help the platelets in clotting are measured by clotting tests
(chemicals are added to the plasma in the lab and the time taken to clot is measured) -
see figure
1.
All other chemicals in the blood can be measured in the ‘serum’ or
‘plasma’ (both are blood with the cells removed but are prepared slightly
differently) - see figure
2.
Are my results normal?
All laboratories use slightly different formats for reporting test
results. In the hospitals in figures 1 and 2 the results are simply given.
Some labs print ‘abnormal’ values in red, others give the ‘normal range’ in
brackets afterwards - eg 'sodium 142 mmol/L (130-145 mmol/L)'. The ranges in different hospitals can
differ because different types of tests are used.
There may be specific ranges for men and women or for children. The laboratories
usually use a ‘reference range’ as ‘normal’ ie the values which 95% of
results fall into.
The important thing to remember is that results just outside a range are seldom of any
significance - and those which appear quite abnormal are usually expected by your doctors
and nurses.
There are usually good reasons why you are having blood tests and they are very helpful
in assessing your lymphoma and monitoring your progress.
We regret that Dr Revell is unable to give individual advice
to enquirers. |