Blood test
Blood Film
A blood film is an examination of blood under a microscope to look at the appearance of blood cells, helping diagnose many conditions.
Quick answer
Blood Film: what it is and what the results mean
A blood film (blood smear) is made by spreading a drop of blood on a slide and examining the cells under a microscope. It shows the size, shape and appearance of red cells, white cells and platelets.
- Why it is done: It is used to investigate abnormal full blood count results, unexplained anaemia, infections, and to help diagnose blood disorders including some cancers such as leukaemia.
- Understanding results: The film can show abnormal cell shapes, immature or abnormal cells, parasites, and clues to the cause of anaemia or infection.
What it is
A blood film (blood smear) is made by spreading a drop of blood on a slide and examining the cells under a microscope. It shows the size, shape and appearance of red cells, white cells and platelets.
Why it is done
It is used to investigate abnormal full blood count results, unexplained anaemia, infections, and to help diagnose blood disorders including some cancers such as leukaemia. It can reveal features that automated counts cannot.
What to expect
It uses the same blood sample as a full blood count, taken from a vein in the arm. A trained scientist or haematologist examines the slide, so results may take a little longer.
Understanding the results
The film can show abnormal cell shapes, immature or abnormal cells, parasites, and clues to the cause of anaemia or infection. Findings guide the diagnosis and whether further specialised tests are needed.
Good to know
Risks and limitations
It is a safe blood test. Interpretation depends on the skill of the examiner, and abnormal findings often need confirming with further tests such as bone marrow examination.
Education and reference only. This explains the test in general terms and is not medical advice. Always follow the specific instructions from the team arranging your test, and discuss your results with your clinician.
Answers
Blood Film: frequently asked questions
Why look at blood under a microscope if I have already had a blood count?
Automated counts give numbers, but a blood film shows the actual appearance of the cells, revealing abnormal shapes, immature cells or parasites that numbers alone cannot detect.
Can a blood film detect leukaemia?
It can show abnormal or immature white cells that raise suspicion of leukaemia, prompting confirmatory tests such as bone marrow examination. It is an important first step rather than a final diagnosis.
Related tests
Other blood test investigations
Sources
Where this is drawn from
- NHS — Tests and treatments
- NICE — diagnostic guidance
- British Society for Haematology / relevant professional body
Building patient-education content for tests or procedures?
We create clear, accurate, referenced medical explainers and decision aids for teams.