How is aplastic anemia diagnosed?

Diagnosis of Aplastic Anemia

The diagnosis of aplastic anemia requires a bone marrow biopsy showing severely reduced cellularity (<20% in severe cases), corrected for patient age, along with peripheral pancytopenia and absence of significant dysplasia or abnormal cell clusters. 1

Diagnostic Algorithm

Initial Evaluation

• Complete blood count showing pancytopenia (decreased erythrocytes, granulocytes, and platelets) 2
• Peripheral blood film examination of at least 100 cells to assess for:
  • Presence of dysplasia in granulocytes
  • Presence of blasts
  • Overall cell morphology 3
• Reticulocyte count to assess bone marrow response (typically low in aplastic anemia) 4

Bone Marrow Assessment

• Bone marrow aspirate with 500 cell differential (when possible) to:
  • Examine for dysplasia of erythroid precursors, granulocytes, and megakaryocytes
  • Perform iron stain for ring sideroblast assessment 3
• Bone marrow biopsy (1-2 cm core) is critical and necessary for diagnosis to:
  • Assess cellularity (typically 10% median, range <5-80%)
  • Evaluate for presence of abnormal localization of immature precursors (ALIP)
  • Perform reticulin stain 3, 1

Additional Studies

• Standard cytogenetics/interphase FISH to rule out clonal disorders 3
• Flow cytometry for cell lineage analysis 3
• PNH screening by sensitive flow or molecular technique 3, 1
• Molecular and genetic testing to exclude inherited forms 5

Key Diagnostic Criteria

Positive Findings for Aplastic Anemia

• Severely reduced bone marrow cellularity (<20% in severe cases), age-adjusted 1
• Peripheral pancytopenia 2, 6
• Absence of significant dysplasia in remaining hematopoietic cells 3
• Absence of abnormal localization of immature precursors (ALIP) 3, 1
• Absence of abnormal sideroblasts 3

Exclusion Criteria (Findings that Rule Out Aplastic Anemia)

• Moderate to severe erythroid dysplasia (bi or trinucleated forms, numerous Howell-Jolly bodies, nuclear budding or bridging) 3
• Presence of abnormal sideroblasts (>5 granules surrounding the nuclear membrane or occupying at least 1/3 of the circumference) 3
• Presence of two or more clusters of immature precursors (minimum of three blasts/clusters) in the bone marrow biopsy 3
• Clonal cytogenetic abnormalities 3, 1

Differential Diagnosis Considerations

• Hypocellular myelodysplastic syndrome (H-MDS) - distinguished by presence of unequivocal dysplasia and/or excess blasts 3
• Hypocellular acute myeloid leukemia (H-AML) - affects 5-7% of de novo AML cases, primarily in elderly patients 3
• Paroxysmal nocturnal hemoglobinuria (PNH) - commonly arises in patients with aplastic anemia 6
• Inherited bone marrow failure syndromes 5, 7

Common Pitfalls to Avoid

• Failing to correct bone marrow cellularity assessment for patient age 3, 1
• Inadequate bone marrow biopsy size (should be 1-2 cm core) 3
• Missing focal areas of dysplasia or abnormal precursor clusters in a hypocellular marrow 3
• Overlooking history of genotoxic exposure or therapy that can cause hypocellular marrows resembling aplastic anemia 3, 1
• Misdiagnosing early/pre-MDS as aplastic anemia (focal granulocytic hyperplasia may suggest early MDS) 3

Importance of Accurate Diagnosis

• Mortality from severe aplastic anemia without treatment approaches 70% within 2 years 5
• Treatment approaches differ significantly between aplastic anemia, H-MDS, and H-AML 1
• Early bone marrow transplantation offers the best hope when compatible donors are available 8
• Immunosuppressive therapy is the mainstay of treatment for those without a suitable donor 5, 6