Flow cytometry

March 4, 2023

In pathology, “flow” often refers to flow cytometry, a laboratory test used for analyzing the physical and chemical characteristics of bodily fluids and tissues such as blood and bone marrow. This test allows for the simultaneous analysis of multiple physical and/or chemical characteristics of single cells flowing through an optical and/or electronic detection apparatus. This test is commonly used in the diagnosis and monitoring of blood cancers such as lymphoma and leukemia although it can be used for a variety of other conditions as well.

Why is flow cytometry performed?

• Cell counting: Flow cytometry is used for counting and analyzing the physical characteristics of cells, such as size and complexity. Some types of cells such as blasts cannot be counted using this test.
• Biomarker detection: The technique identifies and quantifies specific biomarkers on the surface or inside cells, which is crucial for diagnosing diseases.
• Diagnosis and monitoring of disease: It’s instrumental in diagnosing blood cancers, immune deficiencies, and infectious diseases by analyzing blood cells’ properties. Flow is also used to monitor treatment effects and to look for recurrent disease.
• Immunophenotyping: This is the process of identifying the presence and quantities of certain cell types in a sample, essential for diagnosing specific types of leukemia and lymphoma, as well as monitoring infectious diseases such as HIV.

How is flow cytometry performed?

1. Sample preparation: A sample containing cells, such as blood, bone marrow, or tissue lysates, is prepared by suspending cells in a buffer solution. Cells may be stained with fluorescent dyes or antibodies tagged with fluorescent markers that bind to specific cell components or markers.
2. Running the sample: The prepared sample is placed in the flow cytometer. The machine uses a fluidic system to draw the sample into a narrow, hydrodynamically focused stream of fluid. Cells are aligned so that they pass through the laser beam one at a time.
3. Detection: As cells pass through the laser, they scatter light, and the fluorescent markers are excited and emit light at various wavelengths. Detectors capture this light (both scattered and emitted fluorescence) and convert it into electrical signals.
4. Analysis: The data collected by the flow cytometer are analyzed using specialized software. Each cell’s properties can be visualized in plots or histograms, allowing for the analysis of thousands to millions of cells in a short period.

How are the results of this test described in a pathology report?

The results of flow cytometry in a pathology report are typically described in a detailed and structured manner, focusing on the specific characteristics and populations of cells analyzed during the test. The content and format of the report can vary depending on the test’s purpose, the type of specimen analyzed, and the specific disease or condition being investigated. However, most flow cytometry reports will include the following key elements:

• Sample Information: Details about the sample tested, including the type of sample (e.g., blood, bone marrow, lymph node tissue), the date of collection, and any relevant patient information.
• Methodology: A brief description of the flow cytometry method used, including information on cell preparation, staining protocols, and the types of fluorescent markers (antibodies) applied.
• Panel of markers: A list of the specific cell surface markers (antigens) and/or intracellular markers tested, along with the fluorescent labels used. This section provides insight into the targets of the analysis, which are critical for identifying specific cell populations.
• Results: This is the core section of the report, presenting the findings from the flow cytometry analysis. Results are often reported as percentages or absolute counts of cells expressing specific markers, indicating the presence and proportion of different cell types within the sample. For example, in the context of leukemia or lymphoma, the report would detail the immunophenotype of the malignant cells, such as CD19+ B cells or CD3+ T cells, and their proportion relative to the entire cell population analyzed.
• Interpretation: The pathologist provides an interpretation of the results, explaining what the findings mean in the context of the patient’s clinical presentation and other laboratory findings. This section may include a diagnosis (e.g., identifying a specific type of leukemia), prognostic information, and recommendations for further testing or treatment.
• Graphics: Some reports may include histograms or scatter plots that visually represent the data obtained from the flow cytometry analysis. These visual aids can help illustrate the distribution and characteristics of the cell populations analyzed.

About this article

Doctors wrote this article to help you read and understand your pathology report. Contact us if you have questions about this article or your pathology report. For a complete introduction to your pathology report, read this article.

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Atlas of pathology