The CD4 count is calculated as the product of the following: White blood cell count (eg, 4000 cells / mcL) Percentage of white blood cells that are lymphocytes (eg, 30%) Percentage of lymphocytes that are CD4+ (eg, 20%) Using the numbers above, the CD4 count (4000 x 0.3 x 0.2) is 240 cells / mcL, or about 1/3 of the normal CD4 count in adults, which is about 750 ± 250/mcL.