Total Red Blood Cells
Total White Blood Cells are present in normal blood in a smaller number than red cells, the normal adult range being between 4,000 and 11,000 per mm3 of blood. White cells are capable of "eating up" bacteria and other harmful particles found in the blood thus, its main function is to act as one of the body’s defenses. Some white cells are also connected with making antibodies which play an important role in providing immunity and resistance to infection. In certain conditions, the white blood cell count may be higher or lower than the normal range. The five main types of white cells present in the blood are the neutrophils, lymphocytes, monocytes, eosinophils and basophiles.
The differential count presents the five main types of white cells, the neutrophils, lymphocytes, monocytes, eosinophil and basophiles as a percentage. Each type of white cell has its own unique function.
• Neutrophils are increased in acute bacterial infection
• Lymphocytes are increased in viral disease
• Monocytes are increased in some bacterial infections and monocytic leukemias
• Eosinophils are increased in allergic conditions and when intestinal parasites are present.
• Basophiles are increased in association with hypersensitivity and allergic responses.
The red blood cell contains a substance called haemoglobin (Hb). Hb consists of an iron-containing red pigment (haem) combined with a protein substance (globin). Hb gives the red cells their colour and their ability to take up oxygen from the lungs which is then delivered to the tissues where it is needed. Iron is the key raw material required by the body to keep the production of Hb up to the normal rate. One of the sources of iron is from food, such as meat, liver, eggs, wholemeal bread and green vegetables.
A person is considered anaemic if the Hb falls below the normal range. Severe anaemia can lead to many conditions including heart failure. Anaemia can be caused by:
a) loss of blood through bleeding,
b) deficiency of iron from food,
c) decreased production of red blood cells, and
d) hereditary disease such as Thalassaemia.
PCV (Packed Cell Volume)
PCV measures the amount of red cells to the volume of the whole blood sample. It is a useful test for the evaluation of haematological disorders such as anaemia and other conditions.
Total Red Blood Cells
Red blood cells transport oxygen to various tissues of the body. Red blood cells also carry carbon dioxide to the lungs to be exhaled. The total red cell count gives an approximation of the number of red cell circulating in the blood. A reduction in their number results in decreased oxygen carrying capacity, and this condition is called anaemia. Causes of anaemia are described under haemoglobin above. A significant increase in red blood cell count is related to a disease called Polycythemia.
Red Blood Cell Indices
MCV (Mean Corpuscular Volume)
MCV measures the average volume of a red cell in an individual’s blood. It is an index calculated from the PCV and total red cell count. It is useful as an aid in classifying anaemias.
MCH (Mean Corpuscular Haemoglobin)
MCH is another index that measures the weight of haemoglobin in a red cell of an individual sample. It is useful for determining the types of anaemia.
MCHC (Mean Corpuscular Hb Count)
MCHC is another index that expresses the amount of haemoglobin in the red cells relative to the size of the cells. It is a useful aid for classifying anaemias.
Red Cell Distribution Width (RDW)
The red cell distribution curve is a useful indicator of erythrocyte population ratio in peripheral blood; for instance, it helps to evaluate the therapeutic effect of transfusion therapy for anaemia, and to discriminate between thalassemia and iron deficiency anaemia. In thalassemia, RDW is usually narrow.
Platelet is another cellular component of blood. The platelets are fragments of the cytoplasm from a large cell called megakaryocyte found in the bone marrow. Platelets play an important role in the clotting of blood and prevention of bleeding. They help stop bleeding by forming a sticky plug to seal vessel walls and also help initiate a series of enzymatic reactions, which result in the formation of the blood clot. Platelet count is an important test used to investigate bleeding disorders, to assess clotting ability, or to, monitor drug treatments. An increase in the platelet count may occur in conditions such as polycythemia or after a spleenectomy. A decrease in the platelet count below normal level is seen in patients with dengue haemorrhagic fever and may occur in leukaemia, some anaemia and certain blood disorder, or following chemotherapy and radiation therapy.
Peripheral Blood Film (PBF)
PBF is a thin smear of blood made on a glass slide and stained with special dyes. It is then examined by a technologist under the microscope providing a vast amount of information on the blood cells. It allows visual estimation of Hb and the overall picture of blood cells. Changes in size, shape and structure of individual RBCs and WBCs can be identified. These changes may have diagnostic significance in certain diseases. Immature forms of blood cells, which are especially significant in cases of leukemia, can also be identified. Overall, the PBF provides useful information on hematological blood disorders, such as anaemia and leukemia.
ESR (Erythrocyte Sedimentation Rate)
As blood is made up of cells suspended in a liquid called plasma, the ESR measures the distance the cells will fall (settle) against the plasma in a fine tube held vertically for one hour. ESR is influenced by two main factors:
1. Properties of the Red Blood Cells: Changes in the size, shape and number of red cells due to certain disease will affect the sedimentation rate.
2. Properties of the Plasma: The amount and type of plasma protein present in a blood sample may affect the ESR. If protein levels are raised, the sedimentation rate may be increased.
ESR is not a specific test for any particular disease. It is used as a screening test for general indication of inflammation. ESR may be helpful in confirming or following the course of inflammatory or other diseases. As a high ESR reading is indicative of an inflammatory process, further investigations may be required to confirm a diagnosis. However it is not uncommon for pregnant females to have elevated ESR readings.
There are two commonly used blood group systems:
The ABO and Rhesus Group.
Under the ABO Group there are four main groups of blood: A, B, AB and O. Every human being belongs to one of these groups. In Singapore, approximately 45% of the population belongs to group O. 25% group A, 25% group B and 5% group AB. The Rhesus (Rh) blood group is the second most important human blood group system. The major antigen (active part) in the Rhesus system is called the D antigen. Red blood cells that possess the D antigen are called Rh (D) Positive and those lacking the D antigen are called Rh (D) Negative.