Is flow cytometry for diagnosing Chronic Lymphocytic Leukemia (CLL) the same as Serum Protein Electrophoresis (SPEP) and Urine Protein Electrophoresis (UPEP)?

Flow Cytometry for CLL Diagnosis is Different from SPEP and UPEP

No, flow cytometry for diagnosing Chronic Lymphocytic Leukemia (CLL) is not the same as Serum Protein Electrophoresis (SPEP) and Urine Protein Electrophoresis (UPEP). These are completely different diagnostic tests that identify different conditions through distinct methodologies 1, 2.

Flow Cytometry in CLL Diagnosis

Flow cytometry is the cornerstone diagnostic test for CLL that:

• Identifies and quantifies specific cell surface markers (immunophenotyping) on B-lymphocytes
• Confirms the clonality of B cells by detecting a characteristic immunophenotype:
  • CD5+, CD19+, CD20+ (dim), CD23+
  • Surface immunoglobulin (dim), CD79b (dim/low)
  • Restricted expression of either kappa or lambda light chains
  • Often CD43+, FMC7 negative, and CD200+ 1, 2, 3

The NCCN guidelines specifically state that flow cytometry of peripheral blood with immunophenotyping is adequate for CLL diagnosis, and bone marrow biopsy is generally not required 1.

SPEP and UPEP

SPEP and UPEP are electrophoretic techniques that:

• Separate proteins in serum or urine based on their electrical charge
• Identify monoclonal proteins (M-proteins) produced by plasma cell disorders
• Are primarily used to diagnose and monitor conditions like multiple myeloma, Waldenström macroglobulinemia, and other plasma cell dyscrasias
• Cannot identify the specific cell surface markers needed for CLL diagnosis

Key Differences

1. Cell type analyzed:

   • Flow cytometry in CLL: Examines B-lymphocytes
   • SPEP/UPEP: Analyzes proteins, particularly immunoglobulins, not cells

2. Methodology:

   • Flow cytometry: Uses fluorescent antibodies to identify specific cell surface markers
   • SPEP/UPEP: Uses electrical charge to separate proteins

3. Diagnostic purpose:

   • Flow cytometry in CLL: Confirms the presence of a monoclonal B-cell population with specific markers
   • SPEP/UPEP: Identifies monoclonal proteins secreted by plasma cells

Diagnostic Algorithm for CLL

1. Initial suspicion: Persistent lymphocytosis (≥5 × 10^9/L B-lymphocytes) for at least 3 months 1

2. Confirmation: Flow cytometry of peripheral blood showing the characteristic CLL immunophenotype 1, 2

3. Additional testing:

   • FISH analysis for del(17p), del(11q), del(13q), trisomy 12
   • IGHV mutation status
   • TP53 sequencing (particularly before treatment) 1, 2

Pitfalls to Avoid

• Don't confuse immunophenotyping with protein electrophoresis: They target different diseases and use different methodologies
• Don't rely on morphology alone: While CLL cells have a characteristic appearance on blood smear, flow cytometry is required to confirm the diagnosis 1
• Don't miss differential diagnoses: Other B-cell lymphoproliferative disorders like mantle cell lymphoma can present similarly but have different immunophenotypes (e.g., CD23-, cyclin D1+) 2, 4

Flow cytometry has become increasingly sophisticated for CLL diagnosis, with newer panels allowing for both diagnosis and minimal residual disease (MRD) assessment in a single tube 5, 6, further distinguishing it from the protein electrophoresis techniques used for plasma cell disorders.