Question

A 68-year-old man presents with persistent fatigue and generalized lymphadenopathy. CBC shows leukocytosis with an absolute lymphocyte count of 35,000/$\mu$L. Which investigation of choice confirms the diagnosis and determines CD markers of CLL?

• A. Bone marrow biopsy
• B. Flow cytometry of peripheral blood
• C. Serum LDH levels
• D. Lymph node excisional biopsy

Hint:

CLL confirmation and CD marker analysis = flow cytometry of peripheral blood.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The clinical features (elderly man, lymphadenopathy, and high absolute lymphocyte count) strongly suggest Chronic Lymphocytic Leukemia (CLL). The question asks for the "investigation of choice" to confirm immunophenotype.
Step 2: Detailed Explanation:

Diagnosis of CLL: According to the iwCLL criteria, a diagnosis of CLL requires a peripheral blood absolute B-lymphocyte count $\geq$ 5,000/µL sustained for at least 3 months.

Flow Cytometry: This is the gold standard for confirmation. It allows for the identification of specific surface markers. CLL cells typically express CD5 (a T-cell marker), CD19, CD20 (weak), and CD23. This "clonality" is what confirms the leukemia.

Bone Marrow Biopsy: While often done for staging or if the diagnosis is uncertain, it is NOT mandatory for the initial diagnosis of CLL because the cells are readily available in the peripheral blood.

Lymph Node Biopsy: This would be the choice for Small Lymphocytic Lymphoma (SLL), but when the blood count is high (>5000), it is classified as CLL, and blood testing is less invasive and preferred.

Serum LDH: This is a non-specific marker of cell turnover and is not diagnostic.

Step 3: Final Answer:
Flow cytometry of peripheral blood is the definitive and least invasive investigation of choice for confirming the diagnosis and immunophenotype of CLL.