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Every result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

Hematology

Complete Blood Count (CBC): What It Measures and How It Is Read

A complete blood count (CBC) is a comprehensive blood test that evaluates the major components of your blood: red blood cells, white blood cells, and platelets. It is one of the most commonly ordered blood tests and provides a broad overview of your overall health.

Results within 5–7 working days after your blood draw (estimate)

What It Measures

The complete blood count is not a single value but a panel: a set of measurements that together give a picture of the cells in your blood. It is the most frequently requested blood test there is.

The panel has three groups. The red series measures your haemoglobin, haematocrit, red cell count and the cell indices MCV, MCH and RDW. The white series measures the total leukocyte count, optionally broken down into the five types in a differential. The third group is the platelet count.

Because these values are measured in one go, your doctor can relate the red series, the white series and the platelets to one another. It is exactly that coherence that makes the blood count informative; picking out a single value says far less.

Why It Matters

The complete blood count is a broad screening test. A single measurement can bring out signs of anaemia, an infection or inflammation, a clotting problem and the production capacity of your bone marrow.

The value lies in the combination. A low haemoglobin with a low MCV points a different way from a low haemoglobin with a high MCV: the first towards iron deficiency, the second towards a deficiency of vitamin B12 or folate. A raised white cell count only takes on meaning once the differential shows which type is elevated.

A normal blood count does not rule out everything. A thyroid disorder, a vitamin deficiency without anaemia or an early kidney problem will not show up here; those need other tests.

When to Test

A complete blood count is requested for a wide range of complaints: persistent fatigue, fever, a suspected infection, pallor, breathlessness on exertion or bruising for no clear reason.

The panel is also used as a general health check, to follow a treatment, and to recheck an abnormality found earlier.

You do not need to fast for it. It is sensible to be well hydrated and not to schedule the blood draw straight after a hard training session: dehydration and exertion shift several values in the panel at once.

Symptoms

Low Levels

Abnormalities in CBC components may present as fatigue, weakness, frequent infections, unusual bleeding or bruising, pale skin, shortness of breath, or dizziness. Specific symptoms depend on which component is affected.

High Levels

Elevated blood components may be associated with headaches, dizziness, flushed skin, increased clotting risk, fever, or signs of infection or inflammation. The significance depends on which specific values are elevated.

Lifestyle Tips

Several values in the blood count respond to circumstances that have nothing to do with illness. Dehydration raises haemoglobin and haematocrit, a hard training session temporarily raises your white cells, and the time of day plays a part too.

So have your blood drawn at rest and well hydrated where possible, and ideally under comparable conditions each time. That makes a comparison with an earlier measurement far more reliable.

A single mildly abnormal value in an otherwise normal blood count is often harmless and disappears on a repeat measurement. What counts is the pattern across several values and over time, together with your symptoms. Always have an abnormal result assessed by a doctor.

Frequently Asked Questions

What is measured in a complete blood count?
The red series (haemoglobin, haematocrit, red cell count, MCV, MCH and RDW), the white series (the leukocyte count, optionally broken down in a differential) and the platelet count.
What is the difference between a blood count with and without a differential?
Without a differential you only get the total white cell count. With a differential the five types (neutrophils, lymphocytes, monocytes, eosinophils and basophils) are counted separately, which shows far more precisely what is going on.
Do I need to fast for a complete blood count?
No, fasting is not needed. It is sensible to be well hydrated and not to schedule the draw straight after hard training, because that temporarily shifts several values.
Can a complete blood count rule everything out?
No. It is a broad screen of the cells in your blood, but a thyroid disorder, a vitamin deficiency without anaemia or an early kidney problem will not show up. Those need additional tests.
What does a single mildly abnormal value mean?
Often little. A single mild deviation in an otherwise normal blood count is usually harmless and disappears on a repeat measurement. Your doctor looks at the pattern across several values and at your symptoms.
How often is a complete blood count useful?
With symptoms, as often as your doctor considers necessary. As a general check without symptoms, once a year is usually ample; measuring more often typically adds no extra information.

Test Products

This marker is included in the following test panels.