Overview
The Nephrotic Pattern
Nephrotic syndrome is a glomerular filtration barrier disorder in which substantial plasma protein is lost into urine.
Nephrotic syndrome is a glomerular filtration-barrier disorder in which substantial plasma protein is lost into urine. The classic pattern is heavy proteinuria—at least 3.5 g in 24 hours or a urine protein-to-creatinine ratio (UPCR) of at least 200 mg/mmol—serum albumin below 25 g/L, peripheral edema, and hyperlipidaemia. The filtration barrier normally restricts albumin through the combined action of the capillary endothelium, glomerular basement membrane, and podocyte slit diaphragms. Podocyte injury or disruption of the slit diaphragm makes that barrier abnormally permeable. Albumin then crosses into the tubular filtrate instead of remaining in the circulation. A patient may describe frothy urine, and urinalysis may show lipiduria or oval fat bodies, but quantitative urine protein and serum albumin establish the pattern more reliably than appearance alone. Albumin loss lowers plasma oncotic pressure. Fluid consequently leaves the intravascular space and collects in dependent tissues, producing periorbital, dependent, genital, or generalized edema. The patient may look fluid overloaded while the effective circulating volume is reduced. The kidneys sense that reduction in perfusion, activate the renin–angiotensin–aldosterone system, and retain sodium and water. That compensatory response...