Haemoglobin (Hb), Red Blood Cell (RBC)
The RBC carries Hb, which is essential for the transport of oxygenated blood from the lungs to the tissues. A state of anaemia is said to exist if the Hb level falls below the reference range. This can be caused by 1) Acute/chronic loss of blood through bleeding 2) A diet which is poor in iron 3) Decreased production of RBCs by the bone marrow and 4) Defective synthesis of haemoglobin due to an inherited disorder of the blood such as thalassaemia.
The blood specimen is passed through a cell analyser and the percentage of cells to plasma is calculated by direct measurement. It is a useful test for the assessment of haematological disorders.
Red Cell Indices (MCV, MCH, MCHC)
The MCV (mean cell volume) measures the average volume of a red blood cell in an individual’s blood. MCH (mean cell haemoglobin) is an index that measures the average content of Hb in a RBC. MCHC (mean cell haemoglobin concentration) is an index that expresses the content of Hb in the RBC relative to the size of the cells. Red cell indices are useful indicators in the classification of anaemia.
Red Cell Distribution Width (RDW)
The cell distribution width is a numerical expression, which correlates with the degree of anisocytosis (variation in volume of the population of RBCs). It is a useful indicator to differentiate thalassaemia (value generally within the reference ranges) from iron deficiency anemia (value generally greater than the reference ranges). However, there are differences in opinion on the usefulness in monitoring the progress of patients on iron therapy for iron deficiency or megaloblastic anaemia. As the patient responds to treatment, the RDW would eventually fall within the reference ranges.
Platelets are one of the cellular components of the blood. It plays an important role in the clotting of blood. Defective production of platelets or a reduction in their numbers would result in prolonged bleeding.
White Blood Cell (WBC), Differential Count
The differential count (DC) separates the WBC into five main types, each of which has its own special function. The Neutrophils are increased in acute bacterial infections. The Lymphocytes migrate freely between the lymph glands and blood. They enter the blood stream via the thoracic duct. Antigenic stimulation (viral infection) produces an increase in the number of lymphocytes in the circulation. The Monocytes help to determine the nature and course of infection. The Eosinophils are increased in allergic conditions as well as in parasitic infections. The Basophils are increased as a response to hypersensitivity and allergic stimulation.
Erythrocytes Sedimentation Rate (ESR)
The ESR measures the fall in the level of RBC against plasma in a special fine tube held vertically for one hour. It is not a specific test for any particular disease but serves as an indicator for any inflammatory process.