What finding in urine microscopy is indicative of acute tubular necrosis?

Acute tubular necrosis (ATN) is characterized by damage to the renal tubules, often due to ischemia or nephrotoxic agents. One of the key findings in urine microscopy that suggests acute tubular necrosis is the presence of epithelial cell casts. These casts form when the epithelial cells from the renal tubules slough off and aggregate in the tubular lumen, which can occur in the setting of tubular injury.

Epithelial cell casts are an indication of injury to the tubular epithelium, a central feature of ATN. They usually contain renal tubular cells and can be observed due to the cellular damage that occurs when the kidneys are exposed to harmful stimuli, such as toxins or prolonged ischemia. The presence of these casts signifies that the injury is primarily affecting the kidneys' filtering and reabsorbing ability, which is a hallmark of acute tubular necrosis.

In contrast, other types of casts seen in urine may indicate different renal pathologies. For instance, broad waxy casts are typically associated with chronic renal disease and represent non-specific changes due to severe renal failure. Red blood cell casts indicate glomerular damage, often related to glomerulonephritis, while hyaline casts can be found in normal or dehydrated