A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 67-year-old man comes to the clinic complaining of fatigue and dizziness for the past 2 months. He reports that he gets tired easily compared to his baseline and feels dizzy when he exerts himself (e.g., when he walks long distances). His past medical history is significant for hypertension that is controlled with lisinopril. A physical examination demonstrates moderate hepatomegaly and lymphadenopathy. His laboratory studies are shown below.
Leukocyte count and differential:
Leukocyte count: 11,500/mm^3
Segmented neutrophils: 40%
Bands: 3%
Eosinophils: 1%
Basophils: 0%
Lymphocytes: 50%
Monocytes: 8%
Hemoglobin: 11.2 g/dL
Platelet count: 120,000/mm^3
Mean corpuscular hemoglobin concentration: 31%
Mean corpuscular volume: 80 µm^3
Reticulocyte count: 3%
Lactate dehydrogenase: 45 U/L
A subsequent flow cytometry test demonstrates CD20+ cells. What is the most likely finding you would expect in this patient?
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A
Low levels of erythropoietinIncorrect. Erythropoietin levels are not a defining feature of CLL; the classic peripheral smear finding is smudge cells.
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B
Low levels of leukocyte alkaline phosphatase (LAP)Incorrect. Low LAP is the hallmark of chronic myeloid leukemia (CML), used to distinguish it from leukemoid reactions — not CLL.
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C
Presence of hairy cellsIncorrect. Hairy cells with cytoplasmic projections characterize hairy cell leukemia, a separate B-cell malignancy with massive splenomegaly and pancytopenia.
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D
Presence of smudge cellsCorrect. Smudge cells (fragile leukemic lymphocytes that rupture on slide preparation) are the classic peripheral-smear finding of CLL.
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E
Forced diuresis with furosemideIncorrect. Loop diuretics increase urine flow but do not selectively trap weak acids; alkalinizing the urine with sodium bicarbonate ion-traps phenytoin (a weak acid) and accelerates its excretion more effectively.
↑ Tap an answer to reveal the reasoning
Answer: D. A 67-year-old with chronic fatigue, lymphadenopathy, hepatomegaly, lymphocytosis (50% lymphocytes on a leukocyte count of 11,500 = 5,750/mm³, mature-appearing), mild anemia and thrombocytopenia, and CD20+ cells on flow cytometry has chronic lymphocytic leukemia (CLL). CLL is a monoclonal proliferation of mature B lymphocytes that co-express CD19, CD20 (B-cell markers), CD23, and CD5 (the unusual T-cell marker that distinguishes CLL from other B-cell neoplasms). It is the most common adult leukemia in Western countries.
The pathognomonic finding on peripheral blood smear is smudge cells (also called "basket cells") — fragile leukemic lymphocytes that rupture during slide preparation, leaving a smear of nuclear material. Their presence on smear strongly supports CLL.
Distractors: Low erythropoietin would not be expected; if anything anemia of chronic disease may have inappropriately low EPO but this is not the most specific finding. Low leukocyte alkaline phosphatase (LAP) is the classic finding in chronic myeloid leukemia (CML), distinguishing it from leukemoid reaction. Hairy cells with thread-like cytoplasmic projections characterize hairy cell leukemia (B-cell, CD11c/CD25/CD103/CD123 positive) — a different entity that classically presents with massive splenomegaly and pancytopenia.
Clinical pearl: "Older adult + lymphocytosis + smudge cells + CD5/CD20+ B cells = CLL."
**Why each option:**
**A.** Erythropoietin levels are not a defining feature of CLL; the classic peripheral smear finding is smudge cells.
**B.** Low LAP is the hallmark of chronic myeloid leukemia (CML), used to distinguish it from leukemoid reactions — not CLL.
**C.** Hairy cells with cytoplasmic projections characterize hairy cell leukemia, a separate B-cell malignancy with massive splenomegaly and pancytopenia.
**D.** Correct. Smudge cells (fragile leukemic lymphocytes that rupture on slide preparation) are the classic peripheral-smear finding of CLL.