Flow cytometry (immunophenotyping) in cats and dogs
Flow cytometry sorts living cells by the proteins on their surface. In dogs and cats it is used mainly when lymphoma or leukaemia is suspected: it shows whether one type of cell has expanded and whether that type is B cells, T cells or something else. It answers part of the question; the vet reads it together with cytology, the blood count and, when needed, a biopsy.
What it shows
Each type of white blood cell carries its own set of proteins (markers) on its surface. In flow cytometry live cells are stained with antibodies that carry a fluorescent label and bind to these markers. A flow cytometer then counts how many cells of each type are present; from the way the cells scatter light it also estimates their size and internal complexity.
The report answers two questions. First, which lineage the cells belong to — for example, T cells or B cells, and among T cells, CD4 or CD8 types. Second, whether the population is uniform: a uniform, expanded population fits a tumour, a mixed one fits a reactive process such as inflammation. In dogs it is often the first choice when lymphoma or leukaemia is suspected in blood, a lymph node or a fluid.
Higher than reference — what it may be a sign of
- A uniform, expanded population — one cell type grown beyond what is expected, or cells with an unusual combination of markers, fits a lymphoproliferative disease such as lymphoma or lymphoid leukaemia.
- B-cell or T-cell type — the report names the lineage; the vet uses it to plan the next steps. Some types have a recognisable pattern, for example T cells that have lost a common leukocyte marker in T-zone lymphoma of dogs.
- Immature “stem cell” marker (CD34) — an objective sign of acute leukaemia; sometimes the lineage of such cells still cannot be named.
These are findings, not a final diagnosis: flow cytometry is never used alone to diagnose a blood or lymphoid cancer, and some lymphoma types need histology to be subtyped.
Lower than reference
A mixed (heterogeneous) population fits a reactive process. It does not settle every case: the antibodies available for animals are limited, and plasma cells cannot be identified by this method. A sample can also be non-diagnostic — too few living cells. When the result is unclear, the laboratory may run PARR on the same sample.
Look at together with
- Cytology or a biopsy of the same site — how the cells look under the microscope; flow cytometry confirms and adds to that impression.
- PARR — a DNA test for clonality. It answers whether the cells come from one clone, but it is not a typing tool; flow cytometry names the cell type.
- White blood cells and lymphocytes — a recent complete blood count is required with a blood sample, because the result relies on absolute counts.
- Thymidine kinase 1 — a blood marker of dividing cells that answers a different question.
Units and conversion
The result has no units. The report is a description: which markers the cells carry, the share of each cell type, cell size, and a written interpretation — for example, “expanded population of B cells, consistent with lymphoma”. In the app it is stored as text, as written on the form.
Reference range
The expected result is on your lab’s form. Each laboratory has its own reference ranges for cell types in blood. A healthy or reactive sample shows a mixed population without an unexpected expanded cell type. Because the test needs living cells in suspension, the sample must reach the laboratory cold and fresh — a sample that is old, frozen or fixed on a slide cannot be tested this way.
Cats and dogs
In cats flow cytometry can be used for a high lymphocyte count in blood and for cells already recognised as tumour lymphocytes on cytology. Fewer antibodies are available for cats than for dogs, so many cases also need PARR, and for suspected intestinal lymphoma PARR on an intestinal sample is preferred. In one large feline study, many samples could not be used because they contained too few cells.
In dogs flow cytometry is the usual first test when tumour lymphocytes are suspected in any tissue, for a high lymphocyte count, and to tell thymoma from lymphoma in the chest. More antibodies exist for dogs than for other species. Blood is not sent unless there is a high lymphocyte count or suspicious cells in the blood.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
- Colorado State University Clinical Hematopathology Laboratory — Principles of Testing and Publications
- Colorado State University Clinical Hematopathology Laboratory — Choose a test
- Colorado State University Clinical Hematopathology Laboratory — Sample Collection and Submission Instructions
- Rout ED, Avery PR. Lymphoid Neoplasia: Correlations Between Morphology and Flow Cytometry. Vet Clin Small Anim 2017
- eClinPath (Cornell University College of Veterinary Medicine) — Leukemia: classification tools (immunophenotyping)
- Merck Veterinary Manual — Lymphoma in Dogs
- Prognostic Utility of the Flow Cytometry and Clonality Analysis Results for Feline Lymphomas. Vet Sci 2024;11(8):331
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.