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Questions and answers

What is a CBC?

The complete blood count (CBC) is the most frequent test during leukemia treatment. Learning to read it helps a great deal.

Last updated: ~1 min read
Three cell groups in one sample
Figure 1.Three cell groups in one sample

01Short answer

A complete blood count counts three main groups of cells: red cells (and haemoglobin), white cells (and their types, the differential) and platelets. In leukemia this test can show the first sign of disease, and during treatment it shows how far counts have fallen and when they recover. Based on the results, the doctor decides about transfusions, infection protection and when the next cycle starts.

02Simple explanation

Haemoglobin reflects oxygen transport, white cells immune defence and platelets clotting.

The differential shows the types of white cell separately: neutrophils, lymphocytes, monocytes and others.

03Scientific explanation

A CBC is measured by automated analysers; if results are abnormal, a blood film is looked at under the microscope for blasts.

The lowest point of counts after chemotherapy is called the “nadir”; recovery usually takes some weeks, depending on the regimen.

04What happens in the body?

The main values

Haemoglobin and haematocrit show anaemia. The total white count and neutrophils help assess infection risk. Platelets show bleeding risk.

What changes in leukemia

At diagnosis the white count may be very high or very low, and blasts may appear in the blood. During treatment all counts fall, then gradually recover.

The laboratory analyser
Figure 2.The laboratory analyser

How to keep track

Record results in a notebook or table: date, haemoglobin, white cells, neutrophils, platelets. This shows the trend and makes talking with the doctor easier.

Ready to discuss the results with the doctor
Figure 3.Ready to discuss the results with the doctor

05From test to decision

The journey of one blood sample.

A sample is taken — Blood from a vein or a line.1A sample is takenBlood from a vein or a line.
The analyser counts — Cells are counted automatically.2The analyser countsCells are counted automatically.
Three lines — Red cells, white cells, platelets.3Three linesRed cells, white cells, platelets.
Discussed with the doctor — The plan is adjusted to the result.4Discussed with the doctorThe plan is adjusted to the result.
The trendThe trend matters more than one number.
DecisionsTransfusions and protection follow the result.

06Key points at a glance

TopicIn brief
The main valuesHaemoglobin and haematocrit show anaemia. The total white count and neutrophils help assess infection risk. Platelets show bleeding risk.
What changes in leukemiaAt diagnosis the white count may be very high or very low, and blasts may appear in the blood. During treatment all counts fall, then gradually recover.
How to keep trackRecord results in a notebook or table: date, haemoglobin, white cells, neutrophils, platelets. This shows the trend and makes talking with the doctor easier.

07Key terms

Haemoglobin
The protein in red cells that carries oxygen.
Differential
The breakdown of white cells by type.
Nadir
The lowest point of counts after chemotherapy.

08Key points

  • A CBC counts three main cell groups.
  • It can be the first sign of leukemia.
  • During treatment counts fall and recover.
  • Recording results is useful.

09Frequently asked questions

How often is the test done?

During treatment sometimes daily, later less often; the team sets the schedule.

Is a slightly abnormal result frightening?

Usually not; the doctor looks at the whole picture.

Do I need to fast?

Usually not for a CBC, but ask if other tests are taken at the same time.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. How often is the test done?

  2. Is a slightly abnormal result frightening?

  3. Do I need to fast?

My questions

12Sources

  1. MedlinePlus (U.S. National Library of Medicine). Complete Blood Count (CBC)
  2. MedlinePlus (U.S. National Library of Medicine). How to Understand Your Lab Results
  3. National Cancer Institute (NCI). Leukemia—Patient Version
  4. National Cancer Institute (NCI). Survivorship: During and After Treatment
  5. NHS (UK). Acute lymphoblastic leukaemia
  6. NHS (UK). Chronic lymphocytic leukaemia
  7. NHS (UK). Chronic myeloid leukaemia
  8. National Cancer Institute (NCI). What Is Cancer?
  9. American Cancer Society. Risk Factors for Acute Myeloid Leukemia (AML)
  10. Cancer.Net (ASCO). Talking With Family and Friends
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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