Health

Wednesday September 27, 2006

Blood count and film

The Doctor Says
By Dr MILTON LUM



Blood is composed of blood cells and plasma. The blood cells, which comprise about 40% of the blood volume, are produced by the bone marrow. There are three main types of blood cells i.e. red blood cells (erythrocytes), white blood cells (leucocytes) and platelets.

The erythrocytes contain the compound, haemoglobin, which binds to oxygen and transports the oxygen to all parts of the body. The erythrocytes are produced by the bone marrow daily to replace the cells that have broken down.

There are different types of leucocytes viz neutrophils, lymphocytes, monocytes, eosinophils and basophils. They play an important role in the body’s immunity as they fight infectious organisms like bacteria, viruses, and parasites.

The platelets play an important role in the formation of clots whenever there is a cut involving any part of the body.

The plasma, which is the liquid component of blood, comprises about 60% of the blood volume. Its major component is water. However, it contains other substances like proteins, electrolytes like sodium, potassium and chloride, antibodies, glucose, fat etc.

The bone marrow produces blood cells, haemoglobin and plasma all the time. In order to do so effectively, sufficient amounts of various food nutrients like iron and some vitamins are required.

Full blood count

This is a blood test that is commonly carried out. After taking the blood from a person, it is put into a bottle that contains substances which prevents the blood from clotting.

A full blood count used to be carried out manually by a laboratory technologist. However, it is the current procedure in most laboratories for the blood sample to be put into a medical device which carries out the following tests automatically viz:

  • measures the amount of haemoglobin in the red blood cells (erythrocytes)

  • counts 0the number of erythrocytes, white blood cells (leucocytes) and platelets per milliliter of blood

  • calculates the proportion of erythrocytes in the blood (haematocrit)

  • measures the size of the erythrocytes and calculates their average size

    Different laboratories may have different ranges of normal values but the differences are not substantial. The normal haemoglobin in men is higher than in women.

    There are several findings that can be detected in the full blood count e.g.

  • when there too few erythrocytes, the condition is called anaemia. This means that the haemoglobin in each erythrocyte is less than normal. Anaemia is more common in women than men, because of periods and pregnancy in the former. A recent cross sectional survey of 1,074 patients in 56 primary health care centres indicated a prevalence of 35 %. There are several causes of anaemia, the commonest of which is a shortage (deficiency) of iron, in which the average size of the erythrocytes is smaller than normal.

  • when there are too many erythrocytes, the condition is called polycythaemia, of which there are various causes.

  • when there are too few leucocytes, the condition is called leucopenia of which there are various causes. Depending on the type of leucocyte, the condition is called neutropenia, lymphopenia, eosinopenia.

  • when there are too many leucocytes, the condition is called leucocytosis, of which there are various causes. Depending on the type of leucocyte, the condition is called neutrophilia, lymphocytosis, eosinophilia, monocytosis and basophilia. Infections are common causes of neutrophilia, lymphocytosis and eosinophilia. Some allergies cause an eosinophilia. Leukaemias also cause an increase in leucocytes. The type of leukaemia is termed according to the type of leucocyte involved.

  • when there are too platelets, the condition is called thrombocytopenia, of which there are various causes including dengue which is an endemic condition in Malaysia. In this condition, the affected person tends to bruise or bleed easily.

  • when there are too many platelets, the condition is called thrombocythaemia of which there are various causes.

    Blood film

    The medical device used to do the full blood count cannot provide all the information required. So the laboratory technician also examines a film of the blood under the microscope.

    Abnormal shaped and sized cells can be detected this way. The malaria parasite is also detected in this manner.

    Additional tests

    Depending on the results from a full blood count and blood film, the doctor may advise additional tests to shed further light on the cause or to confirm the diagnosis.

    For example, if there is anaemia, the blood sample will be examined further by measuring the levels of iron and vitamins in it.

    A bone marrow biopsy may be done if to determine the cause of anaemia and other blood cell conditions.

    In this procedure, a sample of bone marrow, which contains the cells producing the various blood cells, is obtained by aspiration through a needle inserted into the bone marrow of a large bone of the body.

    There may also be other tests that the doctor will advise to elucidate further the abnormalities found in the blood count and/or blood film. Where anything is not clear, it is always advisable to ask the doctor for an explanation.

  • Dr Milton Lum is Chairperson of the Commonwealth Medical Trust. This article provides general information only and is not intended to replace, dictate or define evaluation by a qualified doctor. The views expressed do not represent that of any organisation that the writer is associated with.

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