Smudge cells are remnants of lymphocytes that have no recognizable cell membrane, cytoplasm, or nuclear structure. They are produced when abnormally fragile lymphocytes are ruptured during the physical preparation of a blood smear and are usually associated with chronic lymphocytic leukemia.
What Are Smudge Cells?
Smudge cells (AKA basket cells) are remnants of lymphocytes that have been destroyed or ‘smudged’ during the process of making a blood smear. They typically lack an identifiable cell membrane and have no cytoplasm or nucleus. Sometimes, all that can be seen of a smudge cell is smashed nuclei.
Lymphocytes are thought to become ‘smudged’ because of their increased fragility, which is associated with diseases such as chronic lymphocytic leukemia (CLL).
Formation of Smudge Cells
Smudge cells are abnormally fragile lymphocytes that are damaged by the process of making a blood smear. A blood smear is a test used to examine a patient’s blood cells and is usually performed as a follow-up to an abnormal complete blood cell (CBC) count. A smear can be used as a diagnostic tool for a wide range of blood disorders, including anemia, bone marrow disorders, various infections, leukemia, and lymphoma.
Some blood diseases (such as chronic lymphocytic leukemia) cause lymphocytes to become unusually fragile. These fragile cells are ruptured as they are smeared onto the glass slide and show up under the microscope as smudge cells.
Clinical Significance of Smudge Cells
Smudge cells have been extensively researched as a prognostic tool in patients with chronic lymphocytic leukemia, and are also associated with viral infections such as infectious mononucleosis.
Chronic Lymphocytic Leukaemia
Smudge cells are most often associated with lymphocyte fragility caused by chronic lymphocytic leukemia (CLL). Their presence in a blood sample is not used to diagnose CLL but can be used as a prognostic tool in patients with the disease.
Studies have shown that CLL patients with a higher percentage of smudge cells have a better prognostic outcome than patients with lower smudge cell counts. Patients with 30% or more smudge cells in their blood didn’t require treatment as quickly as those with less than 30%. They also had a better overall survival rate than those with lower smudge cell counts.
Smudge cells have been primarily researched as a prognostic factor in CLL, but are also linked to viral infections such as infectious mononucleosis (IM). One report stated that a peripheral blood smear performed in a patient with IM revealed that around half of the white blood cells in the sample were smudged. Previous studies have also observed high percentages of smudge cells in patients with IM. Therefore, they have applications as a diagnostic tool for IM and, potentially, other viral infections.