Patient Guide

Understanding Your Full Blood Count (FBC/CBC)

Name: Understanding Your Full Blood Count (FBC/CBC) | HealthReview
Creator: Suman Konda
Published: 2026-07-05

The full blood count is the most commonly ordered blood test. It contains 15–20 individual measurements. This guide explains every number on your CBC report.¹

Written by Suman Konda, PharmD, Clinical Pharmacist · Editorial policy · Not medical advice

Last updated: 01 August 2026 · How we check our content

Red blood cell parameters

Parameter	Normal range	What it measures
Haemoglobin (Hb)	Men: 13.5–17.5 g/dL; Women: 12.0–15.5 g/dL	Oxygen-carrying protein: low = anaemia
Haematocrit (HCT/PCV)	Men: 41–53%; Women: 36–46%	Percentage of blood that is red cells
RBC count	Men: 4.5–5.9 M/µL; Women: 4.0–5.2 M/µL	Number of red blood cells
MCV (mean corpuscular volume)	80–100 fL	Size of red cells: low = iron def; high = B12/folate def
MCH (mean corpuscular haemoglobin)	27–33 pg	Haemoglobin per cell: parallels MCV
MCHC	32–36 g/dL	Haemoglobin concentration in cells
RDW (red cell distribution width)	11.5–14.5%	Variation in red cell size: raised in iron def & B12 def

White blood cell parameters

Parameter	Normal range	Clinical meaning when abnormal
WBC (total white count)	4,500–11,000/µL	High = infection/inflammation; low = viral infection, drugs, bone marrow problem
Neutrophils (ANC)	1,800–7,700/µL (40–70%)	Bacterial infection fighter: low (neutropenia) = severe infection risk
Lymphocytes	1,000–4,800/µL (20–40%)	Viral immunity: high in viral infections; low in HIV, steroids
Monocytes	200–800/µL (2–8%)	Chronic infection, TB, monocytic leukaemia
Eosinophils	100–500/µL (1–4%)	Allergy, asthma, parasites: raised in eosinophilic conditions
Basophils	0–100/µL (<1%)	Allergic reactions, chronic myeloid leukaemia

Platelet parameters

Parameter	Normal range	Clinical meaning
Platelet count	150,000–400,000/µL	Low (<150k) = thrombocytopenia: bleeding risk; High (>400k) = thrombocytosis, clot risk
MPV (mean platelet volume)	7.5–12.5 fL	Platelet size: large MPV with low count suggests ITP or platelet destruction

How to interpret anaemia on a CBC

The MCV is the key to classifying anaemia: Low MCV (microcytic): iron deficiency (most common), thalassaemia, anaemia of chronic disease. Normal MCV (normocytic): acute blood loss, anaemia of chronic disease, kidney disease, mixed deficiency. High MCV (macrocytic): vitamin B12 deficiency, folate deficiency, alcohol, hypothyroidism, certain medications (hydroxyurea, methotrexate).

Questions to ask your doctor

Which parameters are outside the normal range?
Is my anaemia microcytic, normocytic, or macrocytic?
Is my white count high: suggesting active infection?
Are my platelets low enough to cause bleeding risk?

Frequently Asked Questions

What does a full blood count measure?

It measures red cells (and haemoglobin), white cells, and platelets: screening for anaemia, infection, immune problems, and bleeding or clotting disorders in a single test.

What are the main things an FBC can reveal?

Common findings include anaemia (low haemoglobin), signs of infection (raised white cells), and low platelets (bleeding risk): each prompting specific follow-up tests.

Should I fast before a full blood count?

No. An FBC doesn't require fasting. You can eat and drink normally beforehand unless other tests taken at the same time need fasting.

References

Sources cited on this page. PubMed links open the original abstract.

Tefferi A, Hanson CA, Inwards DJ. How to interpret and pursue an abnormal complete blood cell count in adults. Mayo Clin Proc. 2005;80(7):923–936. PMID 16007898 · doi:10.4065/80.7.923

Reading the full blood count – each component explained

The full blood count (FBC, also called complete blood count or CBC) is the most frequently ordered blood test in medicine. It measures three cell lines produced by the bone marrow, each with clinical implications:

Red blood cells (RBC) and haemoglobin (Hb): Haemoglobin is the oxygen-carrying protein inside red cells. Normal Hb: men 130–170 g/L; women 120–155 g/L. Below these thresholds = anaemia. The MCV (mean corpuscular volume) classifies anaemia: small (microcytic, below 80 fL – iron deficiency or thalassaemia), normal (normocytic, 80–100 fL – blood loss, chronic disease), or large (macrocytic, above 100 fL – B12/folate deficiency, alcohol, drugs).
White blood cells (WBC) and differential: Total WBC 4–11 × 10⁹/L; the differential breaks this into five types:
- Neutrophils (40–70%): rise in bacterial infection, tissue injury, steroids; fall in viral infection, autoimmune disease, drug toxicity
- Lymphocytes (20–40%): rise in viral infection (EBV, CMV, HIV seroconversion), lymphoma, CLL; fall in HIV, post-chemotherapy
- Monocytes (2–10%): rise in TB, chronic inflammation, monocytic leukaemia
- Eosinophils (1–4%): rise in allergic disease, parasitic infection, eosinophilic conditions; marked rise (above 1.5 × 10⁹/L) = hypereosinophilic syndrome
- Basophils (under 1%): marked rise suggests myeloproliferative disease (CML)
Platelets: Normal 150–400 × 10⁹/L. Below 150 = thrombocytopenia; risk of spontaneous bleeding rises below 50, becomes significant below 20. Above 400 = thrombocytosis – reactive (infection, inflammation, iron deficiency, post-splenectomy) or primary (essential thrombocythaemia).

When an abnormal FBC needs urgent action

Certain FBC findings require same-day assessment regardless of other clinical context:

Haemoglobin below 70 g/L – acute haemorrhage or severe haemolytic crisis
Neutrophils below 0.5 × 10⁹/L (severe neutropenia / agranulocytosis) – infection risk is extreme; any fever in this context is a neutropenic sepsis emergency
Platelets below 10–20 × 10⁹/L – risk of intracranial haemorrhage
Blast cells reported on blood film – suggests acute leukaemia; same-day haematology referral required
"Leukaemoid reaction" (WBC above 50 × 10⁹/L) – extreme leukocytosis from infection, or leukaemia