What urine findings are characteristic of nephrotic syndrome?

In nephrotic syndrome, the hallmark urine findings are the presence of significant amounts of protein and often fatty casts. This condition is characterized by increased permeability of the glomerular filtration barrier, leading to the loss of large amounts of protein in the urine (proteinuria), typically more than 3.5 grams per day. As protein is lost, the urine may also show lipiduria, which includes fatty casts — indicative of the kidney's response to significant protein loss.

These findings are critical because they reflect the underlying pathophysiology of nephrotic syndrome, which involves glomerular injury and altered lipid metabolism, resulting in both protein and fat abnormalities in the urine. The presence of protein and fatty casts can help confirm the diagnosis of nephrotic syndrome in a clinical setting.