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Blood Film

Circulating Blasts

September 8th, 2021


Blasts are not usually present in the peripheral blood; their presence in the circulation is highly abnormal and classically suggestive of acute leukaemia.
Blasts tend to be medium to large cells with a large nucleus that takes up most of the cell (high nuclear : cytoplasmic ratio), fine nuclear chromatin pattern, nucleoli and a grey to blue cytoplasm.
  • Types of Blasts

  • Myeloblast - medium to large cells with high nuclear:cytoplasmic ratio, fine nuclear chromatin, prominent nucleoli, pale blue cytoplasm and intracytoplasmic vacuolesSeen in acute myeloid leukaemia
  • Monoblast - large cells with low to moderate nuclear:cytoplasmic ratio, delicate lacy chromatin, large and prominent nucleoli and light grey cytoplasmSeen in acute monoblastic and myelomonoblastic leukaemia
  • Lymphoblast - small to medium cells with high nuclear:cytoplasmic ratio, open nuclear chromatin, less prominent nucleoli and basophilic cytoplasm without granulesSeen in acute lymphoblastic leukaemia
  • Megakaryoblast - small to medium cells with round or indented nuclei, fine reticular chromatin and basophilic cytoplasm with cytoplasmic blebbingSeen in acute megakaryocytic leukaemia and myeloid neoplasms associated with Down syndrome
  • Causes of Circulating Blasts

  • Acute leukaemia - acute myeloid leukaemia, acute lymphoblastic leukaemia, others
  • Other bone marrow pathologies - e.g. myelodysplastic syndrome, CML, CMML, myelofibrosis
  • Acute stress - sepsis, haemorrhage, shock
  • G-CSF administration
  • Examples

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