Introduction of haematology

Introduction haematology

The word “Haematology" literally means 'study of blood'. In a clinical set-up, a haematology laboratory is concerned with the abnormalities of the constituents of blood, namely the plasma and the blood cells. The laboratory tests performed include enumeration of different types of cells, relative distribution of various categories and their chemical, functional and structural abnormalities. 

Haematological tests are also required as a part of patient's admission report because many diseases show signs and symptoms of haematological nature. These tests are commonly referred to as Complete Blood Count (CBC) and include estimation of haemoglobin, enumeration of red and white blood cells, differential count (i.e. classification of white blood cells), morphological abnormalities of red cells, and platelets.

Since the equilibrium of blood is affected by many factors, haematological tests are useful in assessing the degree of diseases or disorders of haematological or non-haematological origin. Thus, haematological tests can help in the diagnosis of nutritional, metabolic, hereditary, hormonal, neoplastic, drug-induced, inflammatory or infectious disease states.

Blood absorbs oxygen in the lungs, nutrients in the gastro-intestinal system and supplies the tissues with these essential substances. The blood also collects harmful wastes produced as end products of metabolism and transports them to the organs of excretion.

Anaverage healthy adult has blood equivalent to 7-8 % of the body weight. In quantity it is about 6 litres. Blood is mainly composed of plasma, a fluid in which red blood cells (RBC) or erythrocytes, white blood cells (WBC) or leucocytes and platelets or thrombocytes are suspended. The plasma, occupying 55 % of the total volume of blood, contains 90% water, the remaining 10% being proteins, carbohydrates, lipids, hormones, enzymes, vitamins and salts. The majority of cells suspended in plasma are erythrocytes. The leucocytes are much fewer in number than the erythrocytes, while the platelets are associated with blood coagulation mechanism. The erythrocytes contain a high concentration of haemoglobin, a red coloured pigment which acts as the oxygen carrier. Leucocytes exist in different forms, each having a physiological function in the defence mechanism.

Various haematological investigations and their reference values are listed in Table