Blood film

The expected report is that no abnormal features were seen; the wording varies between laboratories, and many films are reported with a descriptive comment rather than a single word.

A blood film is a thin smear of blood on a glass slide, stained and examined under a microscope by a scientist or haematologist. It shows the shape, size and colour of the red cells, the appearance of the white cells and the platelets, and anything unusual such as parasites. The result is a written description rather than a number.

The laboratory often makes a film automatically when the analyser flags something unusual in the full blood count. Doctors also request one when looking into anaemia, unexplained high or low counts, suspected red cell breakdown, malaria and some blood cancers.

• Low iron, vitamin B12 or folate, each of which gives a recognisable pattern
• Inherited red cell conditions such as thalassaemia, sickle cell and spherocytosis
• Red cell breakdown from any cause
• Liver disease and alcohol
• Infections, including malaria and glandular fever
• Blood cancers and bone marrow conditions
• A missing or poorly working spleen

• A report of no abnormal features means the cells looked as expected under the microscope

• Many film comments describe minor findings that are of no importance, and the report usually says so
• A sample that sat for many hours before the film was made shows artefacts that the laboratory recognises
• Platelet clumping in the tube is a common comment and is a sample effect, not an illness

No fasting needed. The film is made from the same tube as the full blood count.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.