To test the levels of lymphocytes in the blood, a doctor usually conducts a complete blood count, a blood cell exam and flow cytometry. Other blood tests may be deemed necessary after the results of these tests are known, according to the American Cancer Society.
The complete blood count determines the amount of white and red blood cells and platelets that are in the body, says the American Cancer Society. This allows the doctor to know the level of lymphocytes present in the blood. In a blood cell exam, a doctor determines whether the patient has lymphocytes that do not look normal by looking at a blood smear under a microscope. The flow cytometry test shows the make-up of the lymphocyte cells in the blood.