Evidence‑Based Diagnostic and Differential Evaluation of Aplastic Anemia

Peripheral Blood Evaluation

At least 100 leukocytes should be counted on the peripheral smear to identify granulocyte dysplasia and to assess for blasts. 1

A bone‑marrow biopsy (core) is mandatory; aspirate alone is insufficient because aplastic anemia typically shows marked paucicellularity. [2][1]
Perform a differential count on ≈ 500 marrow cells to evaluate dysplasia of erythroid precursors, granulocytes, and megakaryocytes. 1
Apply an iron stain; the presence of > 5 ring sideroblast granules surrounding the nuclear membrane rules out aplastic anemia. 1
Obtain a 1–2 cm trephine core and examine 4–5 undistorted fields at 100× magnification to assess cellularity. 1
Conduct a reticulin stain on the core biopsy to evaluate fibrosis. 1

Parameter	Criterion (age‑adjusted)
Normal marrow cellularity	100 – age ± 10 %
Diagnostic hypocellularity	Below the age‑adjusted normal range

Conventional cytogenetics/karyotype is required; it cannot be substituted by FISH or molecular panels. 1
Flow cytometry is essential to exclude abnormal immunophenotypes and to differentiate hypocellular myelodysplastic syndrome (MDS) from aplastic anemia. 1
Paroxysmal nocturnal hemoglobinuria (PNH) screening should be performed with sensitive flow cytometry or molecular assays targeting GPI‑anchored proteins (e.g., CD16, CD55, CD59). 1
Immunohistochemistry for CD34, CD117, and myeloperoxidase helps identify abnormal localization of immature precursors (ALIP). 1

≥ 20 % blasts on marrow aspirate definitively excludes aplastic anemia and establishes acute myeloid leukemia. 1
Moderate‑to‑severe erythroid dysplasia (binucleated/trinucleated forms, numerous Howell‑Jolly bodies, nuclear budding/bridging) indicates MDS/AML rather than aplastic anemia. [2][1]
Abnormal sideroblasts (> 5 granules or occupying ≥ 1⁄3 of the nuclear circumference) are characteristic of MDS/AML and exclude aplastic anemia. 1
ALIP presence (≥ 2 clusters of immature precursors, each with ≥ 3 blasts) supports a diagnosis of MDS. 1
Cytogenetic abnormalities strongly favor MDS over aplastic anemia. [2][1]

Granulocyte‑colony stimulating factor (G‑CSF) may be considered for patients with severe neutropenia and active infection, but continuous use lacks supporting evidence. 3

The American Society of Clinical Oncology recommends a complete history focusing on potential causes including exposure to radiation, toxins, and recent viral infections, as well as previous lymphocyte-depleting therapies and personal or family history of autoimmune disease 4, 5
A physical examination with special attention to spleen size to rule out other hematologic conditions is necessary 4
Laboratory investigations should include complete blood count with differential, peripheral smear, and reticulocyte count, as well as viral studies and nutritional assessments 4, 5
Bone marrow biopsy and aspirate analysis is essential to confirm diagnosis and rule out other conditions 5, 6

The severity of aplastic anemia determines treatment approach, with mild, moderate, and severe grades defined by specific criteria, including ANC, platelet count, and reticulocyte count 4, 5

The American Society of Clinical Oncology recommends hematopoietic stem cell transplantation as the first choice for young patients with severe aplastic anemia who have an HLA-identical sibling donor, and immunosuppressive therapy with horse ATG plus cyclosporine as the standard regimen for patients without a matched donor or those over 40 4, 5
Supportive care, including transfusion support with irradiated and filtered blood products, is necessary for all patients during treatment 5
Growth factor support may be considered as needed 5

Cytogenetic analysis, evaluation for dysplastic features in bone marrow, and flow cytometry for abnormal phenotypes can help distinguish between hypoplastic MDS and aplastic anemia 6
Platelet transfusions may be necessary to maintain safe levels in patients with bleeding complications 5

Weekly CBC during initial treatment is recommended, as well as monitoring for response to treatment, including improvement in blood counts and reduction in transfusion requirements 4
For patients on eltrombopag, regular monitoring of liver function tests and adjustment of dose based on platelet response is necessary 4

Delaying treatment initiation while awaiting complete diagnostic workup can be harmful, and failure to distinguish between aplastic anemia and hypocellular MDS or leukemia can lead to inappropriate treatment 5, 6