What tests are used to rule out Acute Lymphoblastic Leukemia (ALL) and lymphoma?

Diagnostic Tests to Rule Out ALL and Lymphoma

The definitive diagnosis or exclusion of Acute Lymphoblastic Leukemia (ALL) and lymphoma requires a comprehensive diagnostic workup including blood tests, bone marrow examination, and imaging studies, with tissue biopsy being the gold standard for lymphoma diagnosis. 1, 2

Initial Laboratory Evaluation

• Complete Blood Count (CBC) with differential and peripheral blood smear review

  • Evaluates for cytopenias affecting multiple cell lines
  • Identifies presence of abnormal cells/blasts
  • Provides baseline hematologic parameters 1, 2

• Blood Chemistry Profile

  • Comprehensive metabolic panel
  • Liver function tests
  • Tumor lysis syndrome panel (lactate dehydrogenase, uric acid, potassium, phosphates, calcium)
  • Disseminated intravascular coagulation panel (D-dimer, fibrinogen, prothrombin time, partial thromboplastin time) 1

• Serum LDH levels

  • Markedly elevated levels (>900 IU/liter) are suggestive of ALL
  • Critical prognostic marker in most lymphoma subtypes 2, 3

• Beta-2 microglobulin

  • Independent prognostic factor for lymphoma
  • Correlates with tumor burden 2

Bone Marrow Evaluation

• Bone marrow aspiration and biopsy

  • Essential when abnormalities in multiple cell lines are present
  • Required when peripheral blood shows abnormal cells
  • Necessary when leukopenia is severe or persistent without obvious cause 1

• Bone marrow studies should include:

  • Morphologic examination of aspirate, touch imprint, and core biopsy
  • Cytochemistry (MPO and NSE for AML differentiation)
  • Immunophenotyping by flow cytometry
  • Cytogenetic analysis 1, 2

Genetic and Molecular Testing

• Karyotyping of G-banded metaphase chromosomes (conventional cytogenetics) 1

• Interphase FISH assays

  • For detecting major recurrent genetic abnormalities
  • Specific probes for ALL include:
    • BCR-ABL1, ETV6-RUNX1, KMT2A translocations
    • Hyperdiploidy markers (chromosomes 4,10,17)
    • CDKN2A deletions 1

• RT-PCR testing

  • Measures transcript sizes (p190 vs p210) of BCR-ABL1 in B-ALL
  • Detects gene fusions associated with Ph-like ALL 1

• Next-generation sequencing (NGS)

  • For detecting signature or cryptic rearrangements
  • Identifies mutations characteristic of specific ALL subtypes 1, 4

Immunophenotyping

• Multicolor comprehensive flow cytometry

  • Essential to distinguish between B-ALL, T-ALL, AML, or mixed phenotype acute leukemia (MPAL)
  • Evaluates lymphocyte subsets
  • Identifies abnormal immunophenotypes 1, 5

• Immunohistochemistry (IHC)

  • Required when flow cytometry is not available
  • For lymphoma diagnosis, should include markers for:
    • B-cell markers (CD19, CD20, CD79a)
    • T-cell markers (CD3, CD5, CD7)
    • Immaturity markers (TdT, CD34, CD99)
    • Myeloid markers (CD117, CD33, MPO) to exclude MPAL 2, 5

Imaging Studies

• Chest X-ray

  • To rule out mediastinal masses 1

• CT/MRI scan of the head with contrast

  • If neurologic symptoms are observed 1

• Whole body PET/CT scan

  • Recommended if lymphoblastic lymphoma is suspected
  • Essential for lymphoma staging 1, 2

Lymph Node Evaluation

• Surgical excisional lymph node biopsy

  • Gold standard for lymphoma diagnosis
  • Blood tests alone are insufficient for definitive diagnosis 2

• Core biopsies

  • Only performed when lymph nodes are not easily accessible 2

• Fine-needle aspiration

  • Generally inappropriate for initial lymphoma diagnosis 2

CNS Evaluation

• Lumbar puncture and CSF analysis
  • Cell count
  • Cytospin examination
  • Flow cytometry
  • TdT staining 1

Important Diagnostic Pitfalls

• Some ALL cases (particularly with MEF2D::BCL9 gene fusion) may lack typical immature markers (CD34, TdT, CD99) and express markers more commonly seen in mature aggressive B-cell lymphomas (CD5, SOX11, BCL-6, c-MYC), leading to misdiagnosis 4

• Distinction between T-lymphoblastic lymphoma (T-LBL), early T-cell precursor ALL (ETP-ALL), and mixed phenotype acute leukemia (MPAL) requires comprehensive evaluation including bone marrow morphology, cytochemical staining, and flow cytometry analysis 5

• For T-LBL diagnosis, molecular markers of both myeloid and lymphoid tissues need to be included (CD117, CD33, Lys, MPO) 5

• Bone marrow examination is essential to distinguish between T-LBL and T-ALL 5

By following this comprehensive diagnostic approach, clinicians can effectively rule out or confirm the diagnosis of ALL and lymphoma, leading to appropriate treatment decisions that impact patient morbidity, mortality, and quality of life.