Microscopic view of Auer rods within mature neutrophils in bone marrow.

Auer Rods: When Leukemia Shows Up Differently

Kai Mendoza in Health & Wellness December 2025 • 4 min read.

"Unusual presentation of leukemia in a child reveals the importance of recognizing atypical signs"

Leukemia, a cancer of the blood, often presents with a complex array of symptoms and diagnostic markers. While certain indicators are commonly observed, the disease can sometimes manifest in unexpected ways, confounding initial assessments and requiring a keen eye for detail.

A recent case study highlights such an instance, detailing the unique presentation of mixed phenotype acute leukemia (MPAL) in an 11-year-old boy. This case underscores the importance of recognizing atypical signs and symptoms that deviate from the norm, potentially leading to earlier and more accurate diagnoses.

The conventional understanding of leukemia involves the presence of Auer rods, crystalline inclusions found within the cytoplasm of immature blood cells called blasts. However, this case defies expectations by reporting the presence of Auer rods in mature neutrophils, a phenomenon rarely encountered and prompting a reevaluation of diagnostic approaches.

What Makes This Leukemia Case Unique?

Microscopic view of Auer rods within mature neutrophils in bone marrow.

The 11-year-old patient was admitted to the emergency department displaying persistent circumoral impetigo, a skin infection around the mouth. Further examination revealed additional symptoms, including skin pallor, enlarged lymph nodes, and hepatosplenomegaly (enlargement of the liver and spleen). Blood tests indicated an elevated white blood cell count (32.5 × 10º/l), low hemoglobin levels (90 g/l), and a platelet count of 220 × 10°/l, with 73% circulating blasts, signaling a potential hematological malignancy.

A bone marrow examination revealed that 93% of the marrow was infiltrated by homogeneous blast cells characterized by a high nucleo-cytoplasmic ratio, large nucleoli (structures within the nucleus), and an absence of azurophilic granules or Auer rods. This initial finding aligned with typical leukemia presentations.

However, what made this case exceptional was the unexpected presence of Auer rods in mature neutrophils found in both peripheral blood and bone marrow samples. Key details from the study worth knowing:

Peripheral blood (top images) and bone marrow (bottom images)
90% CD45weak, CD34+ and HLA-DR+
Myeloid markers CD13, CD117 and myeloperoxidase.
T-cell markers: CD2, CD99 and cytoplasmic CD3. CD4 and CD8 expression were absent
TP53 mutation and WT1 overexpression were present

Immunophenotypic characterization of the blastic population revealed a specific marker profile: 90% CD45weak, CD34+, and HLA-DR+, with expression of myeloid markers CD13, CD117, and myeloperoxidase. The blasts also expressed T-cell markers CD2, CD99, and cytoplasmic CD3, while CD4 and CD8 expression were absent. Genetic analysis revealed a normal karyotype but identified a TP53 mutation and WT1 overexpression. This unique combination of findings ultimately led to a diagnosis of mixed phenotype acute leukemia T/myeloid, not otherwise specified, according to the 2016 World Health Organization classification.

Why Does This Matter?

This case emphasizes the importance of maintaining a broad differential diagnosis and considering atypical presentations, especially in cases of leukemia. While Auer rods are typically associated with blasts, their presence in mature neutrophils should prompt further investigation and consideration of MPAL. Recognizing such deviations from the norm can lead to more timely and accurate diagnoses, ultimately improving patient outcomes. Further research is needed to fully understand the mechanisms driving Auer rod formation in mature neutrophils and the clinical implications of this unusual phenomenon.

About this Article -

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Everything You Need To Know

What exactly are Auer rods, and why are they mentioned in the context of leukemia?

Auer rods are crystalline inclusions found within the cytoplasm of immature blood cells called blasts. Typically, their presence is a key indicator of certain types of leukemia. However, the significance of Auer rods extends to their atypical presence, as seen when they appear in mature neutrophils. This challenges conventional understanding and highlights the need for vigilance in diagnosing atypical leukemia cases, such as mixed phenotype acute leukemia (MPAL). The detection of Auer rods in unusual cell types can prompt further investigation and potentially lead to earlier and more accurate diagnoses.

What is mixed phenotype acute leukemia (MPAL), and why is it important to identify?

Mixed phenotype acute leukemia (MPAL) is a type of leukemia where the cancerous cells exhibit characteristics of both myeloid and lymphoid lineages. Its importance lies in its diagnostic complexity and the need for accurate classification for appropriate treatment. The implications of MPAL involve specific marker profiles and genetic analyses, such as identifying TP53 mutations and WT1 overexpression, to understand the disease's unique characteristics. Proper diagnosis, according to the 2016 World Health Organization classification, is crucial for determining the best course of action and improving patient outcomes.

What are blasts, and why is their presence significant in leukemia?

In the context of leukemia diagnosis, blasts are immature blood cells found in the bone marrow and peripheral blood. The presence and characteristics of blasts are significant because they are a primary indicator of leukemia. High percentages of circulating blasts, along with specific immunophenotypic markers like CD45weak, CD34+, and HLA-DR+, signal a potential hematological malignancy. The absence of certain expected elements in blasts, or the presence of unexpected elements like Auer rods in other cell types, changes diagnostic approaches and indicates the need for a more detailed investigation.

What are neutrophils, and what does it mean if they contain Auer rods?

Neutrophils are a type of mature white blood cell that plays a crucial role in the immune system by fighting infection. Their typical function is to engulf and destroy pathogens. The importance of neutrophils in the context described is highlighted by the unusual presence of Auer rods within them. This is unexpected, as Auer rods are typically found in blasts. The implications of finding Auer rods in mature neutrophils suggest an atypical presentation of leukemia, requiring further investigation to understand the underlying mechanisms and clinical significance.

What is immunophenotypic characterization, and why is it important in diagnosing leukemia?

Immunophenotypic characterization involves identifying specific markers on the surface of cells to classify them and understand their nature. It's important because it helps in accurately diagnosing different types of leukemia, including mixed phenotype acute leukemia (MPAL). In this context, specific markers like CD45weak, CD34+, HLA-DR+, CD13, CD117, myeloperoxidase, CD2, CD99, and cytoplasmic CD3 are used to define the blastic population. The absence of markers like CD4 and CD8 is also significant. The implications of these marker profiles are critical for differentiating MPAL from other leukemias and guiding treatment decisions.