Primary Hematopoietic and Lymphoid Tissue ›› Bone Marrow ›› Abnormal

Myeloblast with Auer Rod*






Microscopic Features:
  • 3-4x larger than a mature RBC
  • High nuclear to cytoplasmic ratio
  • Round Nucleus with immature chromatin (not clumped)
  • Prominent nucleoli
  • Cytoplasm is scant, gray to pale blue and usually lacks granules
  • One or more red-pink rod shaped structures called Auer rod(s) are noted in the cytoplasm
Normal % blood-PB, marrow-BM, lymphoid tissue-LN:
  • PB: None
  • BM: None
  • LN: None
May Resemble:
  • Promyelocyte
  • Pronormoblast
  • Lymphoblast
  • Monoblast
  • Reactive lymphocyte
Differential Diagnoses:

If in blood or in bone marrow:
Acute myeloid leukemia (AML)
Myelodysplastic Syndromes (specifically RAEB-II)

Classic Immunophenotype:
  • CD34+
  • CD117+
  • HLA-DR+
  • CD13+
  • CD33+
  • (they may have immunophenotypic aberrancies such as gain of CD56 or CD7, etc.)
Cartoon Image:



Misc:
  • Presence of Auer rod is diagnostic of the blasts' Myeloid origin (the only morphologic feature that could reliably distinguish a myeloblast from a lymphoblast) . Note: Other blasts (e.g. lymphoblasts) lack Auer rods