Blast Cell Count in Bone Marrow: Normal Range and Clinical Significance

In healthy adults, blast cells constitute <5% of nucleated bone marrow cells.

Elevated blasts (>5–10%) raise concern for:

• Acute leukemias (AML, ALL) — typically >20% blasts (WHO threshold).
• Myelodysplastic syndromes (MDS) — 5–19% blasts (RAEB-1/2).
• Blastic transformation of CML or MPN.
• Severe infections, growth factor therapy (G-CSF), or recovery from marrow suppression (transient).

Flow cytometry, cytogenetics (karyotype, FISH), and molecular studies (NPM1, FLT3, CEBPA) define lineage and risk stratification.

Any elevated blast count requires hematology referral.