A Full Blood Count (FBC) – also known as a Complete Blood Count (CBC) in the USA -is the most common blood test used to evaluate your overall health.
It measures the three primary types of cells found in your blood: Red Blood Cells, White Blood Cells, and Platelets.
Haemoglobin is the protein in red blood cells that carries oxygen throughout your body.
Normal Haemoglobin Ranges:
Men: 130–170 g/L
Women: 110–150 g/L
Anaemia (Low Hb): A result below the range for your sex. This can cause fatigue and shortness of breath.
Polycythaemia (High Hb): An abnormally high number of red cells, which can thicken the blood.
Note: A level of 120 g/L is considered anaemic for a man, but falls within the normal range for a woman.
White blood cells are the “soldiers” of the immune system, defending against infection, inflammation, and foreign bodies.
Normal Range: 4.0–11.0 x $10^9$/L
Leucocytosis (High Count): Often indicates an active infection, inflammation, or immune response.
Leucopenia (Low Count): Can be caused by viral infections, bone marrow issues, or specific medications, leaving you more vulnerable to illness.
Clinical Insight: It is medically recognized that individuals of African or Afro-Caribbean descent often have a naturally lower white cell count (3.5–3.9 x $10^9$/L). This is a normal genetic variation known as Benign Ethnic Neutropenia and is not a disease.
Platelets are small cell fragments that help your blood clot to stop bleeding.
Normal Range: 150–400 x $10^9$/L
Thrombocytopenia (Low Count): Increases the risk of bruising and bleeding.
Thrombocythaemia (High Count): Can increase the risk of blood clots.
These markers help doctors determine the type of anaemia you might have by looking at the red cells under a microscope.
Mean Cell Volume (MCV): Measures the average size of a red blood cell.
Normal: 80–95 fL
Microcytic (<80): Small cells (often due to iron deficiency).
Macrocytic (>95): Large cells (often due to $B_{12}$ or Folate deficiency).
Mean Cell Haemoglobin (MCH): Measures the average amount of Hb per cell.
Normal: 27–32 pg
An FBC often includes a “differential,” which breaks down the five specific types of white blood cells. This helps identify if an infection is viral, bacterial, or parasitic.
| White Cell Type | Normal Range (x 109/L) | Primary Role |
| Neutrophils | 1.8 – 7.5 | Bacteria & Fungi |
| Lymphocytes | 1.0 – 4.0 | Viruses & Antibodies |
| Monocytes | 0.2 – 0.8 | Cleaning up debris |
| Eosinophils | 0.1 – 0.4 | Allergies & Parasites |
| Basophils | 0.02 – 0.10 | Allergic reactions |
The Full Blood Count is a vital diagnostic tool. Because laboratories use different equipment, always refer to the “Reference Range” printed on your specific lab report.
If any of your values fall outside these windows, your doctor will likely correlate them with your symptoms to find the underlying cause.
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