What is a hallmark feature of acute myeloid leukemia?

Auer rods are an essential characteristic in the diagnosis of acute myeloid leukemia (AML). These are cytoplasmic inclusions that represent fused lysosomes and are typically found in myeloid precursor cells. The presence of Auer rods is indicative of myeloid differentiation and helps to confirm the diagnosis of AML in the context of a patient's clinical presentation and peripheral blood smear findings.

In contrast, thrombocytopenia, while often seen in patients with AML due to marrow infiltration, is not exclusive to this condition and can occur in various other hematological disorders. Smudge cells are primarily associated with chronic lymphocytic leukemia (CLL) and indicate fragile lymphocytes, thus not typical for AML. Rouleaux formations appear in conditions associated with high levels of serum proteins, such as multiple myeloma, but are not specific to any type of leukemia and particularly not to AML. Therefore, the presence of Auer rods distinctly signals acute myeloid leukemia when identifying the disease in a clinical or laboratory setting.