How is acute leukemia identified in a hemogram?

Hemogram Findings in Acute Leukemia

Acute leukemia typically presents with cytopenias (anemia, thrombocytopenia, and/or leukopenia) and circulating blasts on peripheral blood smear, though the complete blood count can be highly variable and occasionally even normal. 1

Typical Hemogram Patterns

Common Presentations

• Leukocytosis with circulating blasts is the classic presentation, with significant variation in white blood cell counts across different acute leukemia subtypes 1
• Anemia is present in the majority of cases at diagnosis, reflecting bone marrow failure from leukemic infiltration 1
• Thrombocytopenia is common, though thrombocytosis can rarely occur, particularly during infection or in certain AML subtypes 2
• Leukopenia may be present instead of leukocytosis, particularly in cases with predominantly bone marrow involvement 1

Blast Count Variability

• Circulating blasts ≥20% in peripheral blood alone is sufficient for AML diagnosis per WHO 2016 criteria, without requiring bone marrow examination 3
• Aleukemic leukemia (no circulating blasts) or low peripheral blast counts can occur despite significant marrow involvement, making peripheral blood assessment alone unreliable 4
• Normal peripheral blood counts do not exclude acute leukemia, and bone marrow assessment remains essential even when peripheral counts appear normal 4

Critical Diagnostic Pitfall

The most important caveat is that acute leukemia can present with a completely normal hemogram, particularly in pre-B acute lymphoblastic leukemia with extramedullary disease. 5 This extremely unusual presentation can delay diagnosis when clinicians rely solely on peripheral blood findings 5.

When to Suspect Leukemia Despite Normal Hemogram

• Severe bone pain with osteopathy involving multiple bones, even with normal complete blood count 5
• Extramedullary manifestations (lymphadenopathy, hepatosplenomegaly, CNS symptoms) without peripheral blood abnormalities 5
• Constitutional symptoms (fever, night sweats, weight loss) unexplained by peripheral blood findings 3

Specific Subtype Variations

Acute Promyelocytic Leukemia (APL)

• Coagulopathy (prolonged PT/PTT, low fibrinogen) is common at presentation and should prompt immediate DIC profile testing 3
• Leukocytosis >40,000/mcL defines high-risk APL with different treatment implications 3

Acute Leukemia with Monocytic Differentiation

• Higher white blood cell counts are characteristic, with increased risk of leukostasis requiring emergency leukapheresis 3
• CNS involvement is more common, necessitating lumbar puncture at first remission 3

Acute Megakaryoblastic Leukemia

• Myelofibrosis may cause dry tap on bone marrow aspiration, requiring trephine biopsy 6
• Platelet dysfunction and coagulation factor deficiencies (particularly factor V) can occur despite variable platelet counts 6

Essential Diagnostic Algorithm

Because hemogram findings are unreliable for excluding acute leukemia, bone marrow aspirate with morphologic examination of ≥500 nucleated cells is the gold standard and cannot be substituted by peripheral blood assessment alone. 4

Required Testing Sequence

1. Complete blood count with differential examining for blasts, cytopenias, and abnormal cell morphology 1
2. Peripheral blood smear review by experienced pathologist, noting that flow cytometry cannot replace morphologic blast counting 4
3. Bone marrow aspirate and biopsy mandatory even with normal peripheral counts if clinical suspicion exists 4
4. Coagulation studies (PT, PTT, fibrinogen) before any invasive procedures, particularly if APL suspected 3

Special Cytogenetic Considerations

Certain AML subtypes with specific cytogenetic abnormalities [t(8;21), inv(16), t(15;17)] are diagnosed as AML regardless of blast percentage and may present with minimal circulating disease. 4 These cases can have deceptively benign-appearing hemograms despite meeting diagnostic criteria for acute leukemia 4.