From the Guidelines
Smudge cells are characteristic morphologic features found in chronic lymphocytic leukemia (CLL), representing damaged or fragile lymphocytes that appear as cell debris, also known as Gumprecht nuclear shadows, on a blood smear examination. These cells are typically small, mature lymphocytes with a narrow border of cytoplasm and a dense nucleus lacking discernible nucleoli and having partially aggregated chromatin, which may rupture during the preparation of the blood smear due to their inherent fragility 1. The presence of smudge cells is a diagnostic feature of CLL, and they can be found admixed with larger or atypical cells, cleaved cells, or prolymphocytes. Some key characteristics of smudge cells include:
- Appearance as amorphous, basophilic (blue-staining) nuclear material without clear cellular structure or intact cell membrane
- Formation due to the rupture of abnormal lymphocytes during blood smear preparation
- Association with reduced expression of vimentin and other cytoskeletal proteins that normally provide structural integrity to lymphocytes
- Potential correlation with disease prognosis in CLL patients, with higher percentages potentially indicating a more favorable outcome in some studies. The diagnosis of CLL requires the presence of at least 5 × 10^9 B lymphocytes/L (5000/L) in the peripheral blood, and the clonality of the circulating B lymphocytes needs to be confirmed by flow cytometry 1.
From the Research
Definition of Smudge Cells
- Smudge cells are ruptured lymphocytes that appear on routine blood smears of patients with chronic lymphocytic leukemia (CLL) 2, 3, 4, 5, 6.
- They are formed when CLL cells are damaged during the blood smear preparation process, resulting in the release of their cytoplasmic contents 6.
Clinical Significance of Smudge Cells
- The percentage of smudge cells on a blood smear has been shown to be a prognostic factor in CLL, with higher percentages associated with better outcomes 3, 4, 5.
- Studies have found that patients with higher smudge cell percentages tend to have longer progression-free periods and overall survival rates 3, 4, 5.
- The enumeration of smudge cells may be a useful indicator of CLL prognosis, particularly in laboratories with limited access to advanced technology 6.
Laboratory Considerations for Smudge Cells
- Smudge cells can affect the accuracy and reproducibility of white blood cell (WBC) differentials, and laboratories may employ different methods to mitigate these errors 2, 6.
- Counting smudge cells as lymphocytes on nonalbuminized blood smears can yield reliable manual differential count (MDIFF) results 2.
- Automated differentials (ADIFFs) can also generate reliable results, but may not be available in all laboratories 2.