A blood film is a test that involves smearing a drop of blood on to a glass slide for examination under a microscope. The blood film is stained with dyes to make the blood cells show up clearly. The test allows the shape and appearance of blood cells to be checked for any abnormality, for example the sickleshaped red blood cells characteristic of sickle cell anaemia.
The relative proportions of the different types of white blood cells can also be counted. This examination, known as a differential white cell count, may be helpful in diagnosing infection or leukaemia. Blood films are also used in diagnosing infections in which the parasites can be seen inside the red blood cells; an example of such an infection is malaria. Blood film tests are usually carried out together with a full blood count.