What is a CBC report and how do you read it?
A plain-language walk through the complete blood count (CBC): haemoglobin, red cell indices, white cells and platelets, and why results need a doctor's context.
What a CBC measures
A complete blood count (CBC) is one of the most common blood tests. It counts the main types of blood cells and describes their size. It is a screening tool, so it helps a doctor decide what to look at next rather than naming a diagnosis on its own.
The red cell section
- Haemoglobin (Hb): the oxygen-carrying protein. Low values suggest anaemia.
- Haematocrit (Hct/PCV): the share of blood made up of red cells.
- Red cell count (RBC): how many red cells there are.
- MCV: the average size of the red cells. Small, normal or large cells point towards different groups of causes.
- MCH and MCHC: how much haemoglobin is in each cell.
- RDW: how varied the cell sizes are.
The white cell section
White blood cells (WBC or TLC) fight infection. Reports usually split them into neutrophils, lymphocytes, monocytes, eosinophils and basophils. Short-term changes are common during infections, so one result is rarely enough on its own.
Platelets
Platelets help blood to clot. Counts can rise or fall for many reasons. Read more in our article on high or low platelet counts.
How to read your own report
- Look at the reference range printed next to each result on your report.
- Note which values are flagged, and by how much.
- Look at the pattern across the report, not one number.
- Compare with earlier reports, using the same laboratory if possible.
- Write down questions for your doctor.
When to talk to a doctor
Speak to a doctor if you have symptoms, if a result is far outside the range, or if results keep changing. Seek urgent care for severe breathlessness, chest pain, fainting or heavy bleeding.
If you would like to discuss your reports with the doctor, see reports review. A previous attended visit is required for that service.
Frequently asked questions
What does a "high" or "low" flag on my report mean?
The flag only shows that a number is outside the laboratory's reference range. It does not say why, and a small difference is often not a problem. A doctor interprets the result alongside your symptoms and history.
Can I compare reports from two different laboratories?
Be careful. Different laboratories and machines can use different reference ranges, so compare each result with the range printed on its own report.