What is the clinical significance and interpretation of T and B Cells by Flow Cytometry (Fluorescence-Activated Cell Sorting, FACS), a laboratory test analyzing lymphocyte subsets in serum or plasma to diagnose immunological disorders?

From the Guidelines

Flow cytometry is a laboratory technique that analyzes cell characteristics by suspending cells in a fluid and passing them through an electronic detection apparatus, and the T and B Cells by Flow Cytometry test specifically evaluates the number and types of lymphocytes in a blood sample, focusing on T cells (CD3+, CD4+, CD8+) and B cells (CD19+ or CD20+), as described in the study by 1. The T and B Cells by Flow Cytometry test is typically performed on whole blood samples (not serum or plasma) and requires special handling to preserve cellular integrity. Some key points to consider when interpreting the results of this test include:

• Normal adult values for lymphocyte populations, such as CD3+ T cells (700-2100 cells/μL), CD4+ T helper cells (300-1400 cells/μL), CD8+ T cytotoxic cells (200-900 cells/μL), and CD19+ B cells (100-500 cells/μL) 1.
• Abnormalities such as decreased CD4+ T cells (seen in HIV infection, where counts below 200 cells/μL indicate severe immunodeficiency), reduced B cells (common in X-linked agammaglobulinemia or after rituximab therapy), abnormal CD4:CD8 ratios (normally 1.0-4.0), or global lymphopenia affecting multiple subsets (seen in combined immunodeficiencies) 1.
• Increased populations may indicate lymphoproliferative disorders, with monoclonal expansions suggesting malignancy. The test helps diagnose primary immunodeficiencies, monitor HIV progression, evaluate immune reconstitution after transplantation, and detect certain leukemias and lymphomas, as outlined in the practice parameter for the diagnosis and management of primary immunodeficiency by 1. When interpreting the results of the T and B Cells by Flow Cytometry test, it is essential to look for these specific abnormalities and to consider the clinical context in which the test is being performed, as recommended by 1.

From the Research

Flow Cytometry: T and B Cells Test

• Flow cytometry is a technology used for the multi-parametric analysis of single cells in solution, providing rapid and detailed information about cell populations 2.
• The T and B cells test by flow cytometry is used to analyze the immune system, specifically the T and B cell populations, to diagnose and monitor various immunological disorders.

Specifics of the Test

• The test involves staining the cells with fluorescent antibodies that bind to specific markers on the surface of T and B cells, such as CD3 for T cells and CD19 for B cells 3, 4.
• The stained cells are then analyzed using a flow cytometer, which detects the fluorescent signals and provides information about the number and characteristics of the T and B cell populations.
• The test can be used to detect abnormalities in the T and B cell populations, such as changes in the number of cells, changes in the expression of specific markers, or the presence of abnormal cell populations.

Interpretation of the Test

• The results of the test are typically interpreted by a healthcare professional, who will look for abnormalities in the T and B cell populations, such as:
  • Changes in the number of T or B cells
  • Changes in the expression of specific markers on the surface of T or B cells
  • The presence of abnormal cell populations, such as cancer cells
• The interpretation of the test results will depend on the specific clinical context and the patient's medical history 5, 6.

Abnormalities to Look for

• Abnormalities in the T and B cell populations can indicate a range of immunological disorders, including:
  • Immunodeficiencies, such as antibody deficiencies 5
  • Autoimmune disorders, such as rheumatoid arthritis or lupus
  • Cancer, such as leukemia or lymphoma 6
• The test can also be used to monitor the response to treatment and to detect any changes in the immune system over time.