What is the primary clinical manifestation of nephrotic syndrome?

The primary clinical manifestation of nephrotic syndrome is proteinuria. Nephrotic syndrome is characterized by a significant loss of protein in the urine, typically defined as urine protein excretion exceeding 3.5 grams per day. This occurs due to damage to the glomerular filtration barrier, leading to increased permeability, which allows proteins, mainly albumin, to leak into the urine.

The high levels of protein in the urine result in hypoalbuminemia (low albumin levels in the blood), which contributes to the development of edema as the oncotic pressure in the blood is reduced. Although edema is a common and significant manifestation of nephrotic syndrome, it is a consequence of the underlying proteinuria rather than a primary feature. The presence of hypertension can also occur, but it is not a defining trait of nephrotic syndrome. Hematuria is typically not a characteristic finding in nephrotic syndrome, distinguishing it from other kidney conditions.

Thus, the key feature that defines nephrotic syndrome and differentiates it from other renal disorders is the profound proteinuria.