Table 1B. Comparison of the bone marrow histological features for hypoplastic refractory cytopenia of childhood and aplastic anemia in children.^4-6,23.

	Hypoplastic refractory cytopenia of childhood	Aplastic anemia in children
Cellularity	Hypocellular	> 95% fatty marrow
Dysplastic changea	≥2 cell lineages or ≥10% of cells within one cell lineage	None
Blastb	<5%	No increase
Erythropoiesis	Patchy distribution Left shift Increased mitoses Abnormal localizationc	Absent or single small focus; <10 cells with maturation No abnormal localizationc
Granulopoiesis	Marked decrease Left shift	Absent or markedly decreased, with very few small foci with maturation
Megakaryopoiesis	Marked decrease or aplasia Dysplastic changes Micromegakaryocytes Abnormal localizationc	Absent or very few non-dysplastic megakaryocytes No abnormal localizationc
Lymphocytes	May be increased focally or dispersed	May be increased focally or dispersed
CD34+precursor cells	No increase No clusters	No increase No clusters
KIT+ (CD117+) precursor cells	No increase	No increase
KIT+ (CD117+) mast cells	Slightly increased	Slightly increased

a. The number of lineages and percentage of dysplastic change are evaluated on bone marrow aspirate smears.

b. The blast percentage is evaluated in bone marrow aspirates and biopsy.

c. Abnormal localization indicates the presence of erythopoiesis or megakaryopoiesis in the paratrabecular region.