CBC Blood Test Explained: What Each Value Means

What Is a CBC?

A Complete Blood Count (CBC) is the most commonly ordered blood test, providing a comprehensive snapshot of your blood's cellular components. It is used to diagnose anaemia, infections, inflammatory conditions, blood cancers, and monitor treatment response.

Key Values Explained

Red Blood Cells (RBC)

Normal: Men 4.5–5.9 million/μL; Women 4.0–5.2 million/μL. Low (anaemia): fatigue, pallor, breathlessness. High (polycythaemia): increased clot risk.

Haemoglobin (Hb)

Normal: Men 13–17 g/dL; Women 12–15 g/dL; Children varies by age. Low = anaemia (iron deficiency most common; also B12, thalassaemia). Hb below 8 g/dL is severe anaemia.

MCV (Mean Corpuscular Volume)

Small (microcytic, MCV <80): iron deficiency or thalassaemia. Large (macrocytic, MCV >100): B12 or folate deficiency, liver disease, medications.

White Blood Cells (WBC) — 4,000–11,000/μL

High (leukocytosis): infection, inflammation, stress, steroids, rarely leukaemia. Low (leukopenia): viral infections, medications, immune disorders.

Neutrophils (Normal 40–75%)

High (neutrophilia): bacterial infection, steroids. Low (neutropenia): risk of serious infection below 0.5 × 10⁹/L.

Eosinophils (Normal 1–6%)

High (eosinophilia): allergies, asthma, parasitic infections.

Platelets — 150,000–400,000/μL

Low (thrombocytopenia): dengue, ITP, bone marrow problem, medications. High (thrombocytosis): reactive (infection, iron deficiency) or rarely bone marrow disorder.

FAQ

Do I need to fast for a CBC test? No — CBC does not require fasting. However, if your CBC is part of a panel that includes fasting tests (lipid profile, FBS), fast for the entire panel.

Can a CBC diagnose leukaemia? An abnormal CBC (very high WBC, very low platelets, abnormal-looking cells on peripheral smear) raises suspicion and prompts further investigation. Diagnosis requires bone marrow biopsy.