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Diagnosis and tests

How flow cytometry shows the type

The related article (“Flow cytometry (immunophenotyping)”) explains blood tests. This topic shows, step by step, how flow cytometry identifies the type of leukaemia, using “gating”, and what the result means for treatment.

Last updated: ~1 min read
Three narrowing plots.
Figure 1.Gating plots — How flow cytometry shows the type

01Short answer

Flow cytometry shows thousands of cells as dots on a plot. A specialist first does “gating”: grouping cells by size and structure, then selecting the suspicious group, for example blasts with weak CD45. Next they look at which markers that group carries. In normal marrow, the cells of each lineage mature along an orderly “path”; in leukaemia, an unusual group appears off that path. The marker combination shows the type: CD34, CD117, CD33 and MPO mean myeloid (AML); CD19, CD10 and TdT mean B-ALL; cytoplasmic CD3 and CD7 mean T-ALL; CD5, CD19 and CD23 mean CLL. Some markers are also treatment targets: whether CD20, CD19, CD22 or CD33 is present helps choose matching antibody or cell therapies.

02Simple explanation

Gating: separating groups.

A marker combination: the type.

Target markers: choosing treatment.

03Scientific explanation

Maturation paths: marker intensity on normal cells changes predictably as they mature; leukaemia cells “deviate” from this pattern.

Target loss: after treatment aimed at a target such as CD19, the marker can be lost at relapse, so flow cytometry is repeated.

04What happens in the body?

Gating

Each plot narrows the cells down to a smaller group.

Normal and abnormal

In leukaemia, an unusual group appears beside the orderly ones.

Two plots side by side.
Figure 2.Normal and abnormal groups.

A target marker

A surface marker can be a “lock” for treatment.

A key fitting a marker.
Figure 3.A target marker and an antibody.

05Identifying the type

Four steps.

All cells — A cloud of dots.1All cellsA cloud of dots.
Gate — Blasts selected.2GateBlasts selected.
Markers — Colours checked.3MarkersColours checked.
Type — Lineage named.4TypeLineage named.

06Marker pattern and type

Marker patternType
CD34, CD117, CD33, MPOAML
CD19, CD10, TdTB-ALL
Cytoplasmic CD3, CD7T-ALL
CD5, CD19, CD23CLL
CD11c, CD25, CD103Hairy cell leukaemia

07Key terms

Gating
Selecting groups of cells on a plot.
CD45
A marker on all white cells.
Target marker
A protein that treatment is aimed at.
Maturation path
The normal pattern of cell development.
Antigen loss
A marker disappearing.

08Key points

  • Flow cytometry gates cell groups.
  • An abnormal group points to leukaemia.
  • The marker combination gives the type.
  • It finds target markers.
  • It may be repeated at relapse.
  • Your doctor explains the result.

09Frequently asked questions

CD33 positive: what does that mean?

The cells carry CD33; this may be considered when choosing some AML treatments.

Why repeat flow cytometry at relapse?

Markers can change, which affects the choice of treatment.

Can I have the plots?

Yes, but discuss the main points with your doctor (“Reading your results with your doctor”).

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. CD33 positive: what does that mean?

  2. Why repeat flow cytometry at relapse?

  3. Can I have the plots?

My questions

12Sources

  1. National Cancer Institute (NCI). Definition: flow cytometry
  2. National Cancer Institute (NCI). Adult ALL treatment (PDQ), patient version
  3. National Cancer Institute (NCI). Adult AML treatment (PDQ), patient version
  4. Leukemia & Lymphoma Society. Myelodysplastic Syndromes
  5. Cancer Research UK. Getting diagnosed with acute myeloid leukaemia
  6. MedlinePlus. Recognizing medical emergencies
  7. Leukemia & Lymphoma Society. Diagnosing leukemia
  8. World Health Organization / IARC. WHO Classification of Tumours: Haematolymphoid Tumours, 5th edition (2022)
  9. MedlinePlus Genetics. Cytogenetically normal acute myeloid leukemia
  10. NHS. Acute lymphoblastic leukaemia: Diagnosis
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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