Aplastic Anemia: Diagnosis and Treatment

Diagnosis

The diagnosis of aplastic anemia should be suspected in any patient presenting with pancytopenia. Aplastic anemia is a diagnosis of exclusion.³⁴ Other conditions associated with peripheral blood pancytopenia should be considered, including infections (HIV, hepatitis, parvovirus B19, cytomegalovirus, Epstein-Barr virus, varicella-zoster virus), nutritional deficiencies (vitamin B12, folate, copper, zinc), autoimmune disease (systemic lupus erythematosus, rheumatoid arthritis, hemophagocytic lymphohistiocytosis), hypersplenism, marrow-occupying diseases (eg, leukemia, lymphoma, MDS), solid malignancies, and fibrosis (Table).⁷

Diagnostic Evaluation

The workup for aplastic anemia should include a thorough history and physical exam to search simultaneously for alternative diagnoses and clues pointing to potential etiologic agents.⁷ Diagnostic tests to be performed include a complete blood count with differential, reticulocyte count, immature platelet fraction, flow cytometry (to rule out lymphoproliferative disorders and atypical myeloid cells and to evaluate for PNH), and bone marrow biopsy with subsequent cytogenetic, immunohistochemical, and molecular testing.³⁵ Typical findings in aplastic anemia include peripheral blood pancytopenia without dysplastic features and bone marrow biopsy demonstrating a hypocellular marrow.⁷ A relative lymphocytosis in the peripheral blood is common.⁷ In patients with a significant PNH clone, a macrocytosis along with elevated lactate dehydrogenase and elevated reticulocyte and granulocyte counts may be present.³⁶

The diagnosis (based on the Camitta criteria³⁷ and modified Camitta criteria³⁸ for severe aplastic anemia) requires 2 of the following findings on peripheral blood samples:

• Absolute neutrophil count (ANC) < 500 cells/µL
• Platelet count < 20,000 cells/µL
• Reticulocyte count < 1% corrected or < 20,000 cells/µL.³⁵

In addition to peripheral blood findings, bone marrow biopsy is essential for the diagnosis, and should demonstrate a markedly hypocellular marrow (cellularity < 25%), occasionally with an increase in T lymphocytes.^7,39 Because marrow cellularity varies with age and can be challenging to assess, additional biopsies may be needed to confirm the diagnosis.²⁹ A 1- to 2-cm core biopsy is necessary to confirm hypocellularity, as small areas of residual hematopoiesis may be present and obscure the diagnosis.³⁵

Excluding Hypocellular MDS and IMFS

Excluding hypocellular MDS is challenging, especially in the older adult presenting with aplastic anemia, as patients with aplastic anemia may have some degree of erythroid dysplasia on bone marrow morphology.³⁶ The presence of a PNH clone on flow cytometry can aid in diagnosing aplastic anemia and excluding MDS,³⁴ although PNH clones can be present in refractory anemia MDS. Patients with aplastic anemia have a lower ratio of CD34+ cells compared to those with hypoplastic MDS, with 1 study demonstrating a mean CD34+ percentage of < 0.5% in aplastic anemia versus 3.7% in hypoplastic MDS.⁴⁰ Cytogenetic and molecular testing can also aid in making this distinction by identifying mutations commonly implicated in MDS.⁷ The presence of monosomy 7 (-7) in aplastic anemia patients is associated with a poor overall prognosis.^34,41

Peripheral blood screening using chromosome breakage analysis (done using either mitomycin C or diepoxybutane as in vitro DNA-crosslinking agents)⁴² and telomere length testing (of peripheral blood leukocytes) is necessary to exclude the main IMFSs, Fanconi anemia and telomere biology disorders, respectively. Ruling out these conditions is imperative, as the approach to treatment varies significantly between IMFS and aplastic anemia. Patients with shortened telomeres should undergo genetic screening for mutations in the telomere maintenance genes to evaluate the underlying defect leading to shortened telomeres. Patients with increased peripheral blood breakage should have genetic testing to detect mutations associated with Fanconi anemia.