A decreased anion gap with multiple myeloma is associated with which formation?

In the context of multiple myeloma, a decreased anion gap is commonly associated with the presence of rouleaux formations. These formations arise due to an increase in serum proteins, particularly immunoglobulins, which is a hallmark of multiple myeloma. The elevated levels of proteins lead to a variation in the way red blood cells interact with each other, causing them to stack or form columns that resemble a roll of coins—hence the term "rouleaux."

This stacking of red blood cells can impair their normal flow and filtration through the microcirculation. Additionally, rouleaux formations are typically seen in conditions with elevated plasma proteins, which aligns with the pathophysiology of multiple myeloma. When interpreting laboratory findings, the presence of rouleaux can help to understand the underlying pathology reflected in tests like the complete blood count and the serum protein electrophoresis.

The other formations listed, such as Auer rods, schistocytes, and smudge cells, are indicative of different pathological processes. Auer rods are associated with acute myeloid leukemia, schistocytes with microangiopathic hemolytic anemia, and smudge cells with chronic lymphocytic leukemia. Therefore, rouleaux formations are specifically linked to the abnormalities found