Auer rods are a feature sometimes found in cancerous blood cells. They can be seen under a microscopic and may be uncovered during diagnostic tests for leukemia. Auer rods are most often seen in cases of acute myeloid leukemia (AML), but they may occasionally occur in other blood disorders. The presence of auer rods can help your doctor accurately diagnose your cancer and better predict your outlook.

What Are Auer Rods?

When blood doctors or pathologists (doctors who specialize in diagnosing diseases) examine blood samples, they typically first look at cells under a microscope, often after staining them with dyes to make certain features stand out. This process is called a peripheral blood smear. A blood cell’s appearance is often different when it’s cancerous, so studying its shape, size, and features within a sample can help a medical professional make a diagnosis.

Some types of white blood cells (WBCs) — called granulocytes — contain small particles called granules. One type, azurophilic granules, can be stained with a blue dye called azure A. Azurophilic granules are tiny sacs full of enzymes. These granules digest and remove pieces of bacteria cells or virus particles after white blood cells destroy germs. Auer rods are clumps of abnormal-looking azurophilic granules.

Experts believe that Auer rods form as a result of abnormalities in how the granules develop or function. Under the microscope, Auer rods look like thin red or purple lines or needle-shaped rods. They appear darker than the surrounding area of the cell.

Auer Rods in Disease

Healthy blood cells don’t usually contain Auer rods. However, about 50 percent of people with AML have cells with Auer rods. Doctors most often find Auer rods in specific subtypes of AML, including acute promyelocytic leukemia (APL) and acute myelomonocytic leukemia (AMML).

Auer rods often occur in cases of AML that have specific gene changes. They are frequently seen in leukemia cases that have chromosome translocations, which occur when one piece of DNA breaks off and attaches to a different piece of DNA. Auer rods are associated with two different chromosome translocations: t(8;21)(q22;q22) and t(6;9)(q23;q34).

Doctors have identified Auer rods in other types of blood cancer in rare instances. Auer rods have been found in refractory anemia with excess blasts, a subtype of myelodysplastic syndrome (MDS). Doctors have also seen Auer rods in people with chronic myelomonocytic leukemia type (CMML) type 2 and mixed lineage leukemia. Very rarely, people with other, noncancerous diseases also have cells with Auer rods. For example, Auer rods have been found in typhoid fever. Scientists don’t yet know why Auer rods can be present in these conditions.

Which Cells Have Auer Rods?

Auer rods can appear in different types of cells during disease. To better understand where auer rods are found, it helps to know more about normal and cancerous blood cells.

All types of blood cells develop from stem cells found in the bone marrow (the spongy tissue found inside of your bones). Stem cells are very immature, undeveloped cells. When they divide, they create precursor or progenitor cells that are slightly more mature. The progenitor cells can either be lymphoid cells or myeloid cells. Lymphoid cells go on to make the white blood cells found in the immune system. Myeloid progenitor cells go on to produce red blood cells, certain types of WBCs, and the cells that make platelets (the factors in the blood responsible for creating blood clots).

Auer rods are most often seen in immature myeloid progenitor cells, including cells called promyelocytes or myeloblasts. Rarely, Auer rods may also appear in other types of cells during blood cancers. Doctors have found cases where Auer rods have formed in mature myeloid cells including neutrophils, myelocytes, or monocytes.

Auer Rods and AML Diagnosis

Auer rods can help pathologists learn more about the blood cells within a sample. Their presence indicates that the cell is a type of myeloid cell. Auer rods also indicate the presence of a neoplasm (abnormal growth of cells). Neoplasms include cancers like AML as well as MDS and myeloproliferative neoplasms. Auer rods can help confirm a diagnosis of AML.

If your doctor sees Auer rods in your blood or bone marrow samples, they may look for other signs of leukemia. Your doctor may recommend taking bone marrow or lymph node samples for additional laboratory tests, or they may suggest that you undergo imaging tests.

Auer Rods and AML Treatment and Prognosis

Auer rods help your doctor confirm that the cancerous cells are from the myeloid lineage. Myeloid and lymphoid cancers are treated differently, so finding Auer rods can help your doctor know for sure they are using the best specific treatment.

Doctors still don’t know exactly how Auer rods affect the progression of leukemia. However, Auer rods may be linked to having a good prognosis. Past studies have found that when people with AML have Auer rods, their leukemia is more likely to disappear after treatment and they have a better chance of living longer. This may not be true for other types of blood cancers that have Auer rods, however. When Auer rods occur in chronic myelomonocytic leukemia, they may be associated with a worse prognosis. Cases of CMML that have Auer rods are often more aggressive and are more likely to progress to AML.

Connect With Others

Life with leukemia can pose many challenges. The good news is that you don’t have to face them alone. MyLeukemiaTeam is the social network for people with leukemia and their loved ones. Here, members from across the world come together to ask questions, offer support and advice, and share stories of their everyday lives with leukemia.

Are you going through diagnostic testing for acute myeloid leukemia? Share your thoughts and experiences in the comments below or by posting on MyLeukemiaTeam.