What is the initial investigation to confirm a diagnosis of chronic lymphocytic leukemia (CLL)?

The initial investigation to confirm a diagnosis of chronic lymphocytic leukemia (CLL) is flow cytometry of peripheral blood. This technique is essential because it allows for the identification of abnormal populations of lymphocytes based on their surface markers. In CLL, the flow cytometry typically reveals a characteristic pattern of B-cell markers (such as CD19, CD23, and weak expression of CD5) that is crucial for making a definitive diagnosis.

While a complete blood count provides valuable information and may indicate lymphocytosis, it is not specific enough to confirm CLL. A bone marrow biopsy might be performed in certain clinical scenarios but is not routinely required for the diagnosis of CLL when flow cytometry and peripheral blood examination provide sufficient information. A CT scan of the abdomen is not utilized for the initial diagnosis of CLL; it may be used later to assess lymphadenopathy or splenomegaly but does not aid in confirming the diagnosis itself. Thus, flow cytometry is the most definitive and specific method for diagnosing CLL in its initial investigation phase.