In distinguishing between nephrotic and nephritic syndrome, what key difference is noted in nephrotic syndrome?

In nephrotic syndrome, the defining feature is the significant amount of proteinuria, which is typically greater than 3.5 grams per day. This high level of protein excretion occurs due to increased permeability of the glomerular filtration barrier, leading to a loss of proteins such as albumin in the urine. The presence of more protein in the urine is what primarily distinguishes nephrotic syndrome from nephritic syndrome, which is characterized by lower levels of proteinuria (generally less than 3.5 grams per day) along with the presence of hematuria and often RBC casts.

Additionally, in nephrotic syndrome, patients often exhibit edema, hyperlipidemia, and hypoalbuminemia due to the loss of protein. This contrast highlights why the degree of protein excretion is a critical factor in categorizing these conditions. The other symptoms associated with nephritic syndrome, such as hematuria and RBC casts, serve to classify it distinctly and do not apply to nephrotic syndrome. Thus, the substantial proteinuria is the hallmark of nephrotic syndrome.