# Calculating Absolute Cell Counts

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The page below is a sample from the LabCE course Introduction to Flow Cytometry: Blood Cell Identification. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Calculating Absolute Cell Counts

Lymphocytes are a specific type of white blood cell. Lymphocytes can either be T cells or B cells. In the mature T cell population, the T cells can either be helper T cells or suppressor/cytotoxic T cells.
Understanding the principles behind the identification of these T cell populations is important. To begin, CD3 marks all mature T cells. Then:
• CD4 marks T-helper cells
• CD8 marks cytotoxic T cells
Therefore, in any given lymphocyte population, the CD4+ cells plus the CD8+ cells should equal the CD3+ cells. This is because the CD4 cells and the CD8 cells will be marked with CD3 since they are both mature T cells.
Provided the total white blood cell (WBC) count and the percentage of lymphocytes from a complete cell count/differential, one can calculate various values. These values include: absolute CD3 counts, CD4 counts, CD8 counts, and CD4:CD8 ratios.
The following results represent a patient sample which is used to calculate the values above:
WBC count= 2.5 x 103/mcL (2500 cells/mcL)
% Lymphs= 30%
Using the following calculation: Absolute (Abs) lymphs= WBC count x 1000 x percent lymphs (expressed as a decimal) we can determine the absolute lymphocyte count per mcL.
2.5 x1000 x 0.30 = 750 lymphs/mcL
*Note: mcL = microliter