Patients often see a reference to smudge cells in their complete blood count (CBC) reports. Smudge cells are cells that are probably damaged during the CBC process. The cell walls rupture, and when seen under the microscope, they look like a smudge; hence the term smudge cells. These cells are probably lymphocytes and are so distorted that they can't be given a "real" name.

Smudge cells are not unique to CLL. However, they are seen much more frequently and in much higher numbers in CLL than in any other condition. For example, in normal specimens, there may be .01 percent. In patients with severe infections or burns, there may be 0.1 to 0.3 percent. In patients with acute leukemias, there may be as many as 1 to 3 percent, but in CLL patients, smudge cells can be up to 20 percent of all cells, or higher.