Blood Test

Complete Blood Count (CBC)

Name: CBC Test (Complete Blood Count): Normal Range & High
Creator: Suman Konda
Published: 2026-07-05

A CBC measures the different cells in your blood: red cells, white cells and platelets. Here's exactly what each number means in plain language.

Written and clinically reviewed by Suman Konda, PharmD, Clinical Pharmacist · Based on peer-reviewed sources · Editorial policy · Not medical advice

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

What is a CBC test?

A Complete Blood Count (CBC) is one of the most common blood tests ordered by doctors. It gives a snapshot of your overall health by counting and examining the different types of cells in your blood. Doctors use it to detect anaemia, infections, clotting problems and many other conditions.

CBC Normal Range Chart

Component	Normal Range (Adults)	Unit
Haemoglobin (Hb): Men	13.5 – 17.5	g/dL
Haemoglobin (Hb): Women	12.0 – 15.5	g/dL
RBC (Red Blood Cells): Men	4.5 – 5.9	million/µL
RBC (Red Blood Cells): Women	4.0 – 5.2	million/µL
WBC (White Blood Cells)	4,000 – 11,000	/µL
Platelets	150,000 – 400,000	/µL
Haematocrit (HCT): Men	41 – 53	%
Haematocrit (HCT): Women	36 – 46	%
MCV	80 – 100	fL
MCH	27 – 33	pg
Neutrophils	40 – 70	%
Lymphocytes	20 – 40	%

What does HIGH haemoglobin mean?

HIGH Haemoglobin above normal

High Hb can mean dehydration, lung disease, living at high altitude, or a condition called polycythaemia vera. Smokers often have slightly higher Hb. Tell your doctor if your Hb is persistently high.

What does LOW haemoglobin mean?

LOW Haemoglobin below normal

Low Hb means anaemia. The most common causes are iron deficiency, B12 deficiency, or folate deficiency. Symptoms include tiredness, breathlessness and pale skin. Your doctor will look at MCV and MCH to find the type of anaemia.

What does HIGH WBC mean?

HIGH WBC above 11,000

High white cells usually mean your body is fighting an infection (bacterial infections raise it most). It can also indicate inflammation, stress, steroid use or rarely blood cancer. Your doctor will look at which type of WBC is high: neutrophils point to bacterial infection; lymphocytes point to viral infections.

What does LOW WBC mean?

LOW WBC below 4,000

Low WBC (leukopenia) can be caused by viral infections (including dengue, typhoid), certain medications, vitamin deficiencies or bone marrow problems. It means your infection-fighting ability may be reduced.

What does LOW platelet count mean?

LOW Platelets below 150,000

Low platelets (thrombocytopenia) increase bleeding risk. In dengue-endemic regions, dengue fever is a very common cause of a sudden platelet drop. Other causes include viral infections, certain medications, liver disease and autoimmune conditions. Below 50,000 is considered serious: seek care immediately.

Questions to ask your doctor

When discussing your CBC report, ask:

Which value is abnormal and by how much?
Do I need a repeat test to confirm?
Could my medications be affecting this?
Do I need any follow-up tests like iron studies or peripheral smear?

Why and when is a CBC ordered?

A complete blood count is requested in a huge range of situations because it screens several body systems at once. Your doctor may order it as part of a routine health check, before surgery, to investigate symptoms such as persistent tiredness, breathlessness, unexplained bruising, recurrent infections or fever, and to monitor conditions or medications that affect the blood, for example chemotherapy, or drugs that can suppress the bone marrow.

Because the CBC measures red cells, white cells and platelets together, a single sample can point towards anaemia, an active infection, inflammation, a clotting tendency, or a bone-marrow problem. It rarely gives a final diagnosis on its own, but it is one of the most useful starting points in medicine, directing which more specific tests are needed next.

How to prepare for a CBC

For a standard CBC, no special preparation is needed. You do not have to fast, and you can eat, drink and take your usual medicines beforehand unless your doctor has combined it with a fasting test such as glucose or cholesterol.

It is helpful to stay well hydrated before the sample is taken, as dehydration can concentrate the blood and mildly skew several values. Tell the person taking your blood if you have fainted during blood tests before, and mention any medicines or supplements, since some (such as iron tablets or steroids) can influence the result.

Reading your CBC in context: the role of indices

The most informative part of a CBC is often not a single number but the pattern. The red cell indices, MCV (average red cell size), MCH and RDW, are especially valuable when haemoglobin is low. A low MCV (small cells) points towards iron deficiency or thalassaemia, whereas a high MCV (large cells) suggests vitamin B12 or folate deficiency, alcohol excess, or thyroid problems.

Similarly, when white cells are raised, the differential count matters: a rise in neutrophils typically indicates a bacterial infection or inflammation, while a rise in lymphocytes more often reflects a viral illness. This is why doctors interpret the whole report together rather than reacting to one flagged value.

Frequently Asked Questions

Do I need to fast before a CBC?

No. A CBC does not require fasting. You only need to fast if it is being taken at the same time as a test that does, such as fasting glucose or a lipid profile.

Can a CBC detect cancer?

A CBC cannot diagnose cancer by itself, but abnormal patterns, such as very high or very low white cells, or unexplained low counts across all cell lines, can be an early clue that prompts further tests like a blood film or bone marrow examination.

How long do CBC results take?

Most laboratories process a CBC within a few hours, and results are often available the same day, as it is run on automated analysers.

Why does my CBC vary between tests?

Small fluctuations are normal and can reflect hydration, recent infection, exercise, time of day, and even the laboratory used. Doctors look at meaningful trends rather than minor changes.

References

The clinical information on this page is based on peer-reviewed sources indexed in PubMed, the biomedical literature database of the US National Library of Medicine.

Ford J. Red blood cell morphology. Int J Lab Hematol. 2013;35(3):351-7. doi:10.1111/ijlh.12082 · PMID 23480230
Rusch JA, van der Westhuizen DJ, Gill RS, Louw VJ. Diagnosing iron deficiency: controversies and novel metrics. Best Pract Res Clin Anaesthesiol. 2023;37(4):451-467. doi:10.1016/j.bpa.2023.11.001 · PMID 39764832