What Do Blood Tests Tell Us?

There can't be many people who have not had some kind of blood test, they're a normal part of the doctor's diagnostic kit. They are also frequently resorted to when the doctor hasn't a clue what's wrong. The full blood count, one of the most commonly used sets of pathology tests, uses whole blood mixed with anticoagulant to stop clot formation. This distinguishes it from biochemical testing on blood where the blood serum or plasma (the watery part of blood) is used

The full blood count examines mostly the cellular components of blood whereas biochemical testing focuses on its chemical constituents.

The Full Blood Count

This group of tests looks directly at the cells of the blood and parameters related to them, largely involving the use of microscopes and automatic cell counters. The major tests involved are listed below.

• Haemoglobin (Hb): this is the red component of blood. Its function is to carry oxygen. It tends to be lower than normal after blood loss and in anaemia.
• Red blood cells (Rbcs):These are the cells which carry the haemoglobin. Clearly they will be reduced in any significant blood loss. The quantity, colour and shape of these cells is examined.
• White blood cells (Wbcs): the cells of the immune system. There are a number of different types such as neutrophils, eosinophils and basophils. From the total count of white cells and the relative numbers of the various types, it's possible get an idea of the state of the immune system. For example an increase in eosinophils suggests that an allergic reaction is taking place. A rise in the total white cell count could point to an infection.
• Platelets: cells that are intimately involved in the clotting process. Some illnesses and some adverse drug reaction can lower the platelet count which may result in spontaneous bleeding.
• Erythrocyte sedimentation rate (ESR): this is a very non-specific test but useful nonetheless. The blood sample is suspended in a thin glass tube and the rate at which the red cells separate from plasma is measured. This rate is increased when any inflammatory processes are going on within the body. This could be due to infection or any kind of autoimmune disease for example.

Limitations of The Full Blood Count.

It should be remembered that blood tests are not always diagnostic. In some instances a blood test can give a precise indication of what's wrong – anaemia for example where the number and condition of the red blood cells can give a very good indication of the type of anaemia the patient is suffering from.

In many other cases the diagnosis is made by a combination of blood test results, the findings from clinical examination and the patient's case history.

This article is for information only. If you have any health concerns you should visit your doctor.

Print Article

Email Article

View All Articles

How to subscribe to feeds