This common blood test can help to diagnose a wide range of illnesses, infections and diseases. Your doctor may arrange further tests to help determine the cause of the abnormality.

The full blood count test:

• counts the total number of red cells, white cells and platelets in the sample.
• determines the ratio of red cells to plasma (‘haematocrit’ or ‘packed cell volume’).
• determines the count of each of the white cell subsets.
• works out the average haemoglobin level in the red cells (MCH).
• measures the average size of the red cells (MCV).
• if required, reviews the blood cells under a microscope (blood smear/film).

Full blood count testing can be used to look for:

• infections
• anaemia.
• causes of tiredness or weakness.
• bleeding or clotting problems.
• exposure to toxic substances.
• response to certain treatments.vitamin or mineral deficiencies.