A complete blood count shows anemia and the bone marrow contains 15% blasts, with peripheral smear showing hyposegmentation. What is the presumptive diagnosis?

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Multiple Choice

A complete blood count shows anemia and the bone marrow contains 15% blasts, with peripheral smear showing hyposegmentation. What is the presumptive diagnosis?

The key idea is that defining AML hinges on blast percentage. AML requires 20% or more blasts in the bone marrow or circulating blood. Here the marrow has 15% blasts, which is below that threshold, so AML is unlikely. The bone marrow shows dysplasia, evidenced by hyposegmentation of granulocytes. Dysplastic features across one or more cell lines point to a myelodysplastic syndrome rather than a straightforward leukemia. Within myelodysplastic syndromes, having 10–19% blasts in the marrow fits the category of myelodysplastic syndrome with excess blasts (RAEB), specifically RAEB-2, which aligns with the 15% blast figure. The other options don’t fit as well: ringed sideroblasts would be the defining feature of a RARS subtype; monocytosis would suggest CMML; and AML with maturation would require blasts at or above 20%. So the presumptive diagnosis is RAEB, a myelodysplastic syndrome with excess blasts reflecting dysplasia plus a measurable but not qualifying-for-AML blast count.

The key idea is that defining AML hinges on blast percentage. AML requires 20% or more blasts in the bone marrow or circulating blood. Here the marrow has 15% blasts, which is below that threshold, so AML is unlikely.

The bone marrow shows dysplasia, evidenced by hyposegmentation of granulocytes. Dysplastic features across one or more cell lines point to a myelodysplastic syndrome rather than a straightforward leukemia. Within myelodysplastic syndromes, having 10–19% blasts in the marrow fits the category of myelodysplastic syndrome with excess blasts (RAEB), specifically RAEB-2, which aligns with the 15% blast figure.

The other options don’t fit as well: ringed sideroblasts would be the defining feature of a RARS subtype; monocytosis would suggest CMML; and AML with maturation would require blasts at or above 20%. So the presumptive diagnosis is RAEB, a myelodysplastic syndrome with excess blasts reflecting dysplasia plus a measurable but not qualifying-for-AML blast count.

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