Smudge cells are remnants of lymphocytes that have no discernible cell membrane, cytoplasm, or nuclear structure. They occur when abnormally fragile lymphocytes burst during the physical preparation of a blood smear and are usually associated with chronic lymphocytic leukemia.

Smudge cells are fragile lymphocytes that burst when a blood smear occurs
Smudge cells are remnants of lymphocyte cells

What are smudge cells?

Smudge cells (AKA basket cells) are remnants of lymphocytes that were destroyed or “smeared” during the preparation of a blood smear. They typically have no identifiable cell membrane and no cytoplasm or nucleus. Sometimes only shattered nuclei can be seen from a stain cell.

It is believed that lymphocytes become “smeared” due to their increased fragility associated with diseases such as chronic lymphocytic leukemia (CLL).

Formation of smear cells

Muscle cells are burst lymphocytes
Smudge cells are fragile lymphocytes that burst when a blood smear occurs

Smudge cells are abnormally fragile lymphocytes that are damaged by the process of making a blood smear. A blood smear is a test that looks at a patient’s blood cells and is usually done as a follow-up test for an abnormal number of whole blood cells (CBC). A smear can be used as a diagnostic tool for a variety of blood diseases, including anemia, bone marrow disease, various infections, leukemia, and lymphoma.

Some blood disorders (such as chronic lymphocytic leukemia) cause lymphocytes to become unusually brittle. These fragile cells break open when smeared on the slide and appear as smeared cells under the microscope.

Clinical significance of smudge cells

Smear cells have been extensively researched as a prognostic tool in patients with chronic lymphocytic leukemia and have also been linked to viral infections such as infectious mononucleosis.

Smear cells are examined with a blood smear
Blood smear tests are used to check for abnormalities in blood cells

Chronic lymphocytic leukemia

Smudge cells are most commonly associated with the fragility of lymphocytes caused by chronic lymphocytic leukemia (CLL). Its presence in a blood sample is not used to diagnose CLL, but it can be used as a prognostic tool in patients with the disease.

Studies have shown that CLL patients with a higher percentage of wipe cells have a better prognostic outcome than those with lower wipe cell counts. Patients with 30% or more smeared cells in their blood did not need to be treated as quickly as patients with less than 30%. They also had better overall survival than those with lower cell numbers.

Smear cells are usually associated with chronic lymphocytic leukemia
Chronic lymphocytic leukemia is a type of blood cancer

Infectious mononucleosis

Smear cells have been researched primarily as a prognostic factor in CLL, but have also been linked to viral infections such as infectious mononucleosis (IM). One report said that a peripheral blood smear from a patient with IM showed that about half of the white blood cells in the sample were smeared. Previous studies have also seen a high percentage of smeared cells in patients with IM. Hence, they have uses as a diagnostic tool for IM and possibly other viral infections.

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