A sample of your blood will be examined under the microscope to determine whether CLL cells are present.
Flow cytometry is a procedure that examines the molecular charcteristics of cells. It uses a machine that looks for certain substances on or in cells that help identify what types of cells they are (markers). CLL cells usually have a marker called CD5 that is normally found on T-cells, but not on normal B cells.
For someone to have CLL there must be at least 5,000 of these cells (per mm3) in the blood.