The Most Important Blood Test
The Full Blood Count (FBC), known as Complete Blood Count (CBC) in the US, is the single most commonly ordered blood test. It measures three main cell types in your blood and gives your doctor a wealth of information about your overall health.
Red Blood Cells
Haemoglobin (Hb)
The oxygen-carrying protein in red blood cells.- Men: 130 – 170 g/L
- Women: 120 – 150 g/L
- Low = anaemia (many possible causes)
- High = dehydration, lung disease, or polycythaemia
Red Blood Cell Count (RBC)
The number of red blood cells per litre.- Follows similar patterns to haemoglobin
Haematocrit (Hct)
The percentage of blood volume occupied by red cells.- Men: 40 – 52%
- Women: 36 – 48%
MCV (Mean Cell Volume)
The average size of your red blood cells. This is crucial for diagnosing the type of anaemia:- Low MCV (microcytic) — Usually iron deficiency or thalassaemia
- Normal MCV (normocytic) — Chronic disease, kidney disease, or acute blood loss
- High MCV (macrocytic) — B12 or folate deficiency, alcohol, or thyroid problems
MCH and MCHC
Mean cell haemoglobin and concentration. These support the MCV findings.RDW (Red Cell Distribution Width)
Measures variation in red cell size. Elevated in iron deficiency, mixed deficiencies, or early response to treatment.White Blood Cells
Total WBC Count
- Normal: 4.0 – 11.0 × 10⁹/L
- High (leukocytosis) — Infection, inflammation, stress, or rarely leukaemia
- Low (leukopenia) — Viral infections, bone marrow problems, or medications
The Differential
Your WBC is broken down into five types:- Neutrophils (40–70%) — First responders to bacterial infection
- Lymphocytes (20–40%) — Viral defence and immune memory
- Monocytes (2–8%) — Clean-up crew
- Eosinophils (1–4%) — Allergy and parasite defence
- Basophils (0–1%) — Involved in allergic reactions
Platelets
- Normal: 150 – 400 × 10⁹/L
- Low (thrombocytopenia) — Risk of bleeding. Causes include medications, liver disease, and autoimmune conditions
- High (thrombocytosis) — Can be reactive (infection, iron deficiency) or a primary bone marrow problem
MPV (Mean Platelet Volume)
The average size of your platelets. Larger platelets are younger and more active.When to Worry
Most minor abnormalities on an FBC are harmless and resolve on their own. Results that warrant prompt medical attention include:
- Haemoglobin below 70 g/L
- WBC above 30 × 10⁹/L or below 1.0 × 10⁹/L
- Platelets below 50 × 10⁹/L
- Any result flagged as critical by the lab
Track Your Blood Count
CheckMyBloods automatically extracts and categorises all FBC markers from your uploaded blood tests, showing you trends over time and flagging anything outside the normal range.
