What is a distinguishing feature of starch when identified in urine?

A distinguishing feature of starch when identified in urine is that it appears as a highly refractile sphere with a dimpled center. This characteristic comes from the molecular structure of starch granules, which can reflect light in a way that makes them appear very bright and prominent under a microscope. The dimpled appearance is due to the way starch grains are formed and how they aggregate. This distinct morphology aids in differentiating starch from other components that might be found in urine sediments, allowing for more accurate interpretation in clinical settings.

In contrast, the other options describe features of different substances that can be present in urinary sediment, but do not apply to starch. For example, irregular shapes with granular appearances are more indicative of other substances such as amorphous crystals or debris, while a dense cluster of cells would signify cell accumulation or cellular casts. Long, fibrous structures are typically associated with other types of materials, like certain types of proteins or casts, rather than starch granules. Understanding the unique appearance of starch helps in both diagnosis and monitoring of kidney function and related pathologies.