Complete Blood Count (CBC)

What is the CBC test?

CBC parameters18 measured

1. Haemoglobin

   12–17 g/dL

   The oxygen-carrying pigment in red blood cells, low when iron or vitamins run short or blood is lost, high with dehydration or smoking

2. RBC count

   4.5–5.5 mill/cumm

   How many red blood cells are circulating, falling with anaemia or bleeding and rising with dehydration, smoking or life at high altitude

3. Total WBC count

   4000–11000 /cumm

   The overall number of infection-fighting white cells, rising with infection, inflammation or stress and falling with some viral illnesses, medicines or marrow problems

4. Platelet count

   150000–410000 /cumm

   The small cell fragments that clot blood, low in dengue, some infections and marrow disorders, high with inflammation or iron deficiency

5. Haematocrit

   40–50 %

   The share of blood made up of red cells, tracking haemoglobin closely, low in anaemia and high when the body is dehydrated

6. MCV

   83–101 fL

   Mean corpuscular volume, the average size of a red blood cell, small in iron deficiency and large when certain vitamins are lacking or with heavy drinking

7. MCH

   27–32 pg

   Mean corpuscular haemoglobin, how much haemoglobin each red cell carries, low when iron deficiency leaves cells pale and high when cells are unusually large

8. MCHC

   31.5–34.5 g/dL

   Mean corpuscular haemoglobin concentration, how densely each red cell is packed with haemoglobin, low in iron deficiency and high in some inherited red cell conditions

9. RDW

   11.5–14.5 %

   Red cell distribution width, how much red cells vary in size, rising early in iron or vitamin deficiency before the other counts change

10. MPV

    7.5–11.5 fL

    Mean platelet volume, the average size of platelets, rising when the marrow is producing fresh platelets quickly and falling when production is suppressed

11. Neutrophils

    40–80 %

    The share of white cells that fight bacteria, rising with bacterial infection, injury or stress and falling with viral illness or some medicines

12. Lymphocytes

    20–40 %

    The share of white cells that fight viruses and remember past infections, rising with viral illness and falling with stress, steroids or immune suppression

13. Eosinophils

    1–6 %

    The share of white cells linked to allergy and parasites, rising with asthma, eczema, hay fever or worm infection

14. Monocytes

    2–10 %

    The share of white cells that clear debris and long-standing infection, rising with chronic infection, tuberculosis or recovery from an acute illness

15. Basophils

    0–2 %

    The smallest share of white cells, involved in allergic reactions, occasionally rising with allergy, an underactive thyroid or certain blood disorders

16. Absolute neutrophil count

    2000–7000 /cumm

    The actual number of bacteria-fighting neutrophils rather than a percentage, low counts leaving you open to infection and high counts pointing to bacterial infection or stress

17. Absolute lymphocyte count

    1000–3000 /cumm

    The actual number of virus-fighting lymphocytes rather than a percentage, low with immune suppression or acute stress and high with viral or glandular infections

18. Absolute eosinophil count

    40–440 /cumm

    The actual number of allergy-linked eosinophils rather than a percentage, high with allergic conditions, asthma or parasitic worm infection

Reference ranges are the lab's defaults for adults and are printed on the report beside every value

How to prepare

• No fasting is needed.
• Drink water normally and avoid heavy exercise just before the sample, as dehydration and exertion can nudge the counts.
• Take your regular medicines as usual and tell the phlebotomist about any recent fever, infection or blood transfusion.

Who should take it

Anyone with fever, especially fever lasting more than two days or with body ache and rash in dengue season. People who feel tired, weak, breathless or dizzy, or look pale. Women with heavy periods, and pregnant women at each antenatal visit. Children who are not gaining weight or eating well. Anyone with unexplained bruising, bleeding gums or nosebleeds. People on chemotherapy, anti-thyroid drugs, anti-epileptics or other medicines that affect blood counts. Everyone before surgery, and as part of an annual check-up.

Before the visit

Tell your doctor about steroids, chemotherapy, anti-thyroid drugs, anti-epileptics and blood thinners, and about recent infections, vaccinations or a transfusion. Smoking, pregnancy and living at altitude also shift some values, and reference ranges differ for children and pregnant women.

Why take the CBC test?

• Fever or infection: a CBC separates a likely bacterial infection from a viral one and, with a platelet count, is essential in suspected dengue.
• Tiredness or breathlessness: low haemoglobin is the commonest reason, and the red cell indices suggest whether iron or B12 is the cause.
• Bruising or bleeding: unexplained bruises, nosebleeds or heavy periods call for a platelet count.
• Frequent infections or allergy: the white cell differential shows which cells are raised and why.
• Routine and pre-surgery check: it is part of every health check-up and is required before an operation or starting many medicines.

Questions about the CBC test