The three parts of a full blood count
Red cells. Haemoglobin, red cell count and haematocrit show how well your blood can carry oxygen. Low values mean anaemia, which causes tiredness, breathlessness and pale skin. The red cell indices, MCV, MCH and MCHC, describe the size and colour of the cells and help point to the cause: small pale cells usually suggest low iron, and large cells can suggest low B12 or folate.
White cells. The total white cell count and its five types (neutrophils, lymphocytes, monocytes, eosinophils and basophils) reflect the immune system. A high neutrophil count often accompanies a bacterial infection, raised lymphocytes a viral one, and raised eosinophils allergy or asthma. Low counts can follow a viral illness or some medications.
Platelets. The cells that help blood clot. Low platelets can cause easy bruising or bleeding; high platelets can follow infection, inflammation or iron deficiency.
What it cannot tell you
A full blood count shows a pattern, not a diagnosis. It does not measure iron stores, so ferritin is added if anaemia or tiredness is the question. It does not check organ function, cholesterol or hormones. A single value just outside the range is common and often normal for that person, so results are read together and in context.
Do I need to fast?
No. A full blood count can be taken at any time of day.
At Omnia
Our full blood count test in Chiswick costs £54, analysed by Randox and reviewed with you. It is also included in every health check, from Omnia Essential (£90) to the Randox Everyman. If tiredness is the reason you are testing, the Tired All The Time panel adds ferritin, B12, folate, vitamin D and thyroid. See every test and price.