Blood film

Other names: Peripheral Blood Film; Manual Differential; Peripheral Blood Smear; Red Blood Cell Morphology

A blood film test (commonly known as a blood smear) allows doctors to assess the makeup of the blood; the test allows doctors to estimate the number of red blood cells, white blood cells and platelets.

When is the test used?

The blood film test is usually used in conjunction with other blood tests. The test is used to determine the number and appearance of white blood cells, red blood cells and platelets. It is usually ordered if a patient has had a full blood count and the results have come back as abnormal.

The test is usually ordered for patients who have symptoms which may indicate a deficiency or disease which affects the production of blood cells.

The test may also be used when a patient has been prescribed certain types of medication for another health condition, as these can affect blood cell production.

How is the test carried out?

The test can be carried out by taking a full sample from a vein in the arm or using a smaller sample of blood, which is obtained by pricking the tip of the finger, heel (for infants) or ear. The blood sample is placed on a glass slide and stained using a special form of dye; the results can then be interpreted by the technician using a microscope.

What do the test results mean?

There are many different conditions which can affect the number and appearance of blood cells; findings of a blood smear test may include:

  • Red blood cells: results may indicate conditions including anisocytosis (where the blood cells vary in size) and poikilocytosis (where the blood cells vary in shape)
  • White blood cells: a low number of white blood cells may indicate problems with the immune system; further tests will be carried out to achieve an exact diagnosis.
  • Platelets: variations in the number of platelets affects blood clotting; if the number of platelets is too low, the blood will not clot sufficiently and the individual may bleed excessively. If there are too many platelets, this may increase the likelihood of a blood clot forming.

The accuracy of the result may be affected if there are problems during the preparation or analysis of the sample; the result may also be affected if the patient has recently had a blood transfusion.

Specific Blood Tests

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