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Diagnostic Tests: Auer Rods
Overview — What This Is
The structure shown is an Auer rod, which is an eosinophilic, needle-shaped cytoplasmic inclusion found within myeloblasts or promyelocytes. These inclusions are composed of abnormal azurophilic granules and represent crystalline aggregates of myeloperoxidase. Their presence indicates a malignant proliferation of myeloid precursors.
Disease Associated With Auer Rods
Auer rods are pathognomonic for acute myelogenous leukemia (AML).
They may appear in several AML subtypes, but are especially prominent in:
• Acute Promyelocytic Leukemia (APL, M3) — often showing bundles of Auer rods (“faggot cells”), which is a high-yield test clue.
Their presence confirms the myeloid origin of the malignant blasts
When This Is the Correct Answer
You should answer Auer rods / AML when the question presents a patient with:
• Pancytopenia (fatigue, infections, bleeding)
• Peripheral smear showing blasts
• >20% blasts on bone marrow biopsy, meeting diagnostic criteria for acute leukemia
• Systemic symptoms such as fatigue, fever, infections, bruising, or bleeding
Additional diagnostic support includes:
• Myeloperoxidase (MPO) positivity on histochemical staining
• Expression of myeloid markers: CD13, CD33, CD117
• Presence of Auer rods confirms AML over ALL or other hematologic malignancies
In APL (t(15;17)), Auer rods are particularly dense and clinically important because the disease is associated with DIC, and treatment requires all-trans retinoic acid (ATRA).
Overview — What This Is
The structure shown is an Auer rod, which is an eosinophilic, needle-shaped cytoplasmic inclusion found within myeloblasts or promyelocytes. These inclusions are composed of abnormal azurophilic granules and represent crystalline aggregates of myeloperoxidase. Their presence indicates a malignant proliferation of myeloid precursors.
Disease Associated With Auer Rods
Auer rods are pathognomonic for acute myelogenous leukemia (AML).
They may appear in several AML subtypes, but are especially prominent in:
• Acute Promyelocytic Leukemia (APL, M3) — often showing bundles of Auer rods (“faggot cells”), which is a high-yield test clue.
Their presence confirms the myeloid origin of the malignant blasts
When This Is the Correct Answer
You should answer Auer rods / AML when the question presents a patient with:
• Pancytopenia (fatigue, infections, bleeding)
• Peripheral smear showing blasts
• >20% blasts on bone marrow biopsy, meeting diagnostic criteria for acute leukemia
• Systemic symptoms such as fatigue, fever, infections, bruising, or bleeding
Additional diagnostic support includes:
• Myeloperoxidase (MPO) positivity on histochemical staining
• Expression of myeloid markers: CD13, CD33, CD117
• Presence of Auer rods confirms AML over ALL or other hematologic malignancies
In APL (t(15;17)), Auer rods are particularly dense and clinically important because the disease is associated with DIC, and treatment requires all-trans retinoic acid (ATRA).
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