A blood film allows the evaluation of white blood cells (WBCs, leucocytes), red blood cells (RBCs, erythrocytes), and platelets (thrombocytes). These cell are produced and mature in the bone marrow and are released into the bloodstream when needed. WBCs’ main function is to fight infection, while RBCs carry oxygen to the whole of the body. Platelets appear as small cell fragments and, when activated, stick together to form a plug…A blood film allows the evaluation of white blood cells (WBCs, leucocytes), red blood cells (RBCs, erythrocytes), and platelets (thrombocytes). These cell are produced and mature in the bone marrow and are released into the bloodstream when needed. WBCs’ main function is to fight infection, while RBCs carry oxygen to the whole of the body. Platelets appear as small cell fragments and, when activated, stick together to form a plug as one of the first steps to stop bleeding. The number and type of each cell present in the blood changes but is normally maintained by the body within specific ranges. Values can change at times of illness or stress; intense exercise or smoking can also affect cell counts. A blood film is a snapshot of the cells that are present in the blood at the time that the sample is obtained. To produce a blood film, a single drop of blood is spread in a thin layer across a glass slide, dried, and then stained with a special dye. Once the stain has dried the slide is looked at under a microscope by a medical scientist or haematologist. The drop of blood on the slide contains millions of RBCs, thousands of WBCs, and hundreds of thousands of platelets. Under the microscope, the stained WBCs can be easily seen and counted to estimate the number of each type of cell present. In addition, the size, shape and general appearance of the cells can be compared to that of “normal” cells. It is possible to distinguish between the five different types of WBCs and to find their relative percentages by counting 100 consecutive cells. During this examination, the size, shape and colour (indicators of haemoglobin content) of the RBCs can be measured and the number of platelets estimated. How is the sample collected for testing? A blood sample is obtained by inserting a needle into a vein in the arm or by pricking a finger, ear or, in the case of an infant, a heel. Is any test preparation needed to ensure the quality of the sample? No test preparation is needed. See MoreSee Less
