Laboratory Tests for Chronic Lymphocytic Leukemia (CLL)
For diagnosis and initial workup of CLL, obtain a complete blood count with differential, flow cytometry to confirm clonality showing CD5+/CD19+/CD20+/CD23+ phenotype, and comprehensive metabolic panel including LDH, bilirubin, immunoglobulins, and direct antiglobulin test (DAT). 1
Diagnostic Laboratory Tests (Required)
Essential for Diagnosis
- Complete blood count with differential: Must demonstrate ≥5,000 monoclonal B lymphocytes/µL sustained for at least 3 months 1, 2
- Flow cytometry immunophenotyping: This is mandatory to confirm clonality and establish diagnosis 1, 3
- Required markers: CD5+, CD19+, CD20 (dim), CD23+, with kappa or lambda light chain restriction
- Additional markers showing characteristic pattern: dim surface immunoglobulin, dim CD79b, CD200+
- This distinguishes CLL from mantle cell lymphoma (which is typically CD23-negative) 1
Blood Smear Morphology
- Small, mature lymphocytes with narrow cytoplasm border
- Dense nucleus without visible nucleoli
- Partially aggregated chromatin
- Presence of smudge cells (Gumprecht's shadows) 1
Pre-Treatment Laboratory Evaluation (Recommended)
Standard Chemistry Panel 1, 4
- Lactate dehydrogenase (LDH): Prognostic marker
- Bilirubin: Assess for hemolysis or liver involvement
- Serum immunoglobulins: Detect hypogammaglobulinemia
- Direct antiglobulin test (DAT/Coombs): Screen for autoimmune hemolytic anemia
- Beta-2 microglobulin: Important prognostic marker, part of CLL-International Prognostic Index 4
Infectious Disease Screening (Before Treatment) 1, 4
Required prior to chemoimmunotherapy, alemtuzumab, or stem cell transplant:
- Hepatitis B surface antigen and core antibody
- Hepatitis C antibody
- Cytomegalovirus (CMV) serology
- HIV testing
- Consider Hepatitis E if HBV positive 4
Prognostic and Risk Stratification Tests
Cytogenetic Analysis (Strongly Recommended Before Treatment) 1, 4, 2
FISH panel is mandatory - has direct therapeutic implications:
- del(17p): Poorest prognosis, requires BTK inhibitor or BCL2 inhibitor-based therapy
- del(11q): Previously poor prognosis, improved with certain regimens
- Trisomy 12: Intermediate prognosis
- del(13q): Most favorable prognosis when isolated
TP53 mutation analysis: Must be performed by Sanger or next-generation sequencing if del(17p) is absent, as mutations can occur without deletion 4, 2
IGHV Mutation Status 4, 2, 5
- Recommended before first treatment using Sanger or NGS sequencing (preferred over flow cytometry)
- Cut-off: ≤2% mutation defines unmutated IGHV
- Mutated IGHV (>2%): Better prognosis, excellent outcomes with chemoimmunotherapy
- Unmutated IGHV (≤2%): Poorer prognosis, may favor targeted therapies over chemoimmunotherapy
- This test is necessary when considering chemoimmunotherapy 2
Optional Prognostic Tests
- Complex karyotype (≥3 abnormalities): Possible prognostic relevance via CpG-stimulated metaphase cytogenetics 4, 2
- CD38 expression: Prognostic but not used for treatment decisions 6
- ZAP-70 expression: Prognostic but not standardized for routine use 6
Bone Marrow Examination
Not required for diagnosis but strongly recommended in specific situations 1, 4:
- Before initiating myelosuppressive therapies
- Evaluation of unexplained cytopenias
- Non-conclusive immunophenotype
- Baseline assessment for treatment response evaluation in clinical trials
Important Caveats
Common pitfall: Do not rely on imaging (CT scans) for diagnosis or routine staging - clinical examination is sufficient outside clinical trials 1, 4. CT is reserved for symptomatic patients, assessing tumor lysis syndrome risk before venetoclax, or clinical trial protocols.
Differential diagnosis consideration: If CD23 is positive but clinical suspicion for mantle cell lymphoma exists, add cyclin D1 staining or FISH for t(11;14) translocation 1.
Timing: The 3-month duration requirement for lymphocytosis ≥5,000/µL distinguishes CLL from monoclonal B-cell lymphocytosis (MBL), which has lower counts or shorter duration 1, 2.