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 essential. 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 and 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 that 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 x 1000 x 0.30 = 750 lymphs/mcL
*Note: mcL = microliter