A complete blood count (haemogram) is a blood test that gives an idea about a person's general health and any diseases. The cells in the bloodstream and some values related to the cells are measured.

There are basically 3 main cell groups in the bloodstream. The cells responsible for the transport of oxygen and carbon dioxide are erythrocytes (red blood cells). The haemoglobin molecule in the erythrocytes binds oxygen and transports it between the lungs and other tissues. Those involved in the immune system are white blood cells, which are divided into subgroups such as neutrophils, lymphocytes, monocytes, basophils and eosinophils. In case of problems occurring in the blood vessels, the cells that gather in the damaged area and form a clot to prevent the blood from leaving the vessel are called platelets.

What is a haemogram test (complete blood count)?

Haemogram is a blood test to determine the number and proportion of cells in the blood. Since the cells in the bloodstream are produced in the bone marrow, it also provides an indirect evaluation of the bone marrow.

The haemogram test, which is used to evaluate the general health status, the effect of treatment or the disease process, also has a guiding effect in the diagnosis phase for many diseases.

• Infection and inflammation

• Leukaemia and other cancers

• Bone marrow diseases

• Anaemia

• Autoimmune diseases caused by cells involved in body defence attacking organs and tissues

• Thalassemias, including Mediterranean anaemia

How is a haemogram test (complete blood count) performed?

In order to perform the haemogram test, blood must be taken from the person. Blood collection does not need to be done on an empty stomach. The blood sample taken can remain suitable for analysis for up to 10 hours at room temperature, while this period increases up to 18 hours if the storage process is carried out in the refrigerator. A substance called EDTA in the tubes with purple caps prevents the blood from clotting in the tube.

Some of the blood taken is broken down, allowing the haemoglobin molecule in the red blood cells to come out of the cell. In the other part of the blood, only the dilution process is applied and the cells are counted. Counting and calculation processes are performed automatically in blood counting devices.

How is a haemogram test (complete blood count) reported?

In the haemogram test, the number of cells and the calculated ratios are expressed by some abbreviations.

• Red blood cell count (RBC)

• Haemoglobin (HGB)

• Haematocrit (HCT)

• Red blood cell indices (MCV, RDW, MCH, MCHC)

• Platelet count (PLT)

• White blood cell count (WBC)

These parameters are reported according to whether they are higher or lower than the limit values when the complete blood count result document is generated. The limit values used in this reporting process are for the adult age group. Limit values in children vary according to age and gender.

What are the normal values in haemogram test (complete blood count)?

• Red blood cell count (RBC): The main function of red blood cells (erythrocytes) in the body is to transport the respiratory gases oxygen and carbon dioxide. Erythrocytes carry out this task for an average lifespan of about 120 days. The normal RBC value of adults in automatic blood counting devices is between 3.8 and 5.3 million/ml. The number exceeds this limit in diseases such as smoking, living at high altitude, heavy exercise and polycythemia vera in which the production increases. In blood loss, anaemia and pregnancy, the number of erythrocytes may be found to be decreased.

• Mean red blood cell volume (MCV) : The volume of a normal red blood cell varies between 80-100 fl. By determining the increase or decrease in volume, the underlying anaemia disease can be classified. In iron deficiency anaemia and thalassaemia, the volume of erythrocytes is found to be reduced; in anaemias caused by folic acid or vitamin B12 deficiency, the erythrocyte volume is found to be higher than the upper limit value.

• Haemoglobin (Hb) and Haematocrit (Hct): The haemoglobin molecule in the red blood cell is released as a result of the breakdown of erythrocytes in the blood taken. Haemoglobin is measured directly using photometric methods. The average haemoglobin concentration is 11.7-15.5 g/dL. According to the World Health Organisation, a haemoglobin level below 13 g/dL in men and 12 g/dL in women is called anaemia.

  
  

  Haematocrit value is calculated by multiplying the mean erythrocyte volume (MCV) by the number of erythrocytes (RBC). Normal Hct value in adult individuals is between 35-45%.

• Mean red blood cell distribution width (RDW): It is a statistical value expressing the distribution width of red blood cells. While this value is found to be increased in iron deficiency anaemia, it is found to be normal in thalassaemia carriers.

• Mean erythrocyte haemoglobin (MCH): Indicates the average amount of haemoglobin contained in red blood cells. Normal value is between 30-34 picograms. It is low in iron deficiency anaemia and thalassaemia.

• Mean erythrocyst haemoglobin concentration (MCHC): The percentage expression of haemoglobin in red blood cells calculated by dividing haemoglobin (Hb) by haematocrit (Hct). Its normal value is between 30-36%. In a normal erythrocyte, regardless of its size, the amount of haemoglobin is constant between 30-36% as long as its shape does not change. In hereditary spherocytosis, in which the structure of the red blood cells in the form of a disc with a pale centre is disrupted and they take the shape of a sphere, MCHC is found to be higher than normal.

• White blood cell count (WBC): The number of white blood cells (leukocytes), which are involved in body defence, varies in conditions such as infection, inflammation, bone marrow diseases and immunodeficiency. The normal leukocyte count is between 4,400-11,000/mm3. The number of white blood cells can increase during the course of leukaemia, lymphoma, infectious diseases or after a heart attack resulting in tissue loss. A decrease in the number of leukocytes can occur after diseases such as AIDS, which cause a collapse in immunity, the use of certain medications, autoimmune diseases, and treatments that suppress the bone marrow, such as radiotherapy and chemotherapy.

  
  

  There are five types of white blood cells in the bloodstream: neutrophils, eosinophils, basophils, lymphocytes and monocytes. The number of lymphocytes increases in leukaemia and chronic infectious diseases. If the microorganism causing the infection is bacterial, the number of neutrophils increases. Connective tissue diseases cause an increase in the number of monocytes. The number of basophils increases in hypersensitivity reactions, while the number of eosinophils is high in the case of an allergic or parasitic condition.

• Platelet count (PLT): Platelets, the smallest of the cells in the bloodstream, have a lifespan of approximately 9-12 days. Platelets ensure that when a damage occurs in the vessel wall, that area is closed with a clot. Normal platelet count is between 150,000-400,000/ml. In cases of physical stress, exercise, trauma and infection, the platelet count may temporarily increase to between 450,000 and 600,000. Platelet counts above 600,000 are observed in various conditions defined as myeloproliferative disorders, in which stem cells are overproduced in the bone marrow.

  
  

  KIn the case of disseminated intravascular coagulation, in which platelets in the bloodstream are consumed, their number may fall below 400,00 if defence cells attack the platelets or if their production in the bone marrow is suppressed. When the platelet count falls below 50,000, bleeding can occur in various parts of the body. These haemorrhages usually appear as punctate foci or superficial bruises under the skin, but if the platelet count continues to fall, life-threatening internal bleeding can occur. In order to differentiate between these diseases, the volume and distribution width of platelets are calculated in the same way as for red blood cells. The normal value for the mean platelet volume (MPV) is 7.8-11.0 fl.