The CD4 absolute count test otherwise called as the T cell test is a study of a specific kind of White blood cells called the lymphocytes. CD4 cell count is not the measure of all the CD4 cells in the body but the number of blood cells in a cubic millimeter of blood. It helps the doctor to determine the stage and outcome of HIV. This test is crucial because it gives a clear snapshot of the patient's immune system. The doctor decides what can be done to improve one's living based on the results.