Nephrotic Syndrome

Nephrotic syndrome is a pattern of glomerular injury, not one single disease. The classic picture is heavy proteinuria, low serum albumin, peripheral edema, and hyperlipidaemia. The glomerulus normally acts as a finely graded filter: water and small solutes cross, while albumin and other larger plasma proteins remain in the bloodstream. Injury to the filtration barrier, including the podocytes and their slit diaphragms, makes the filter abnormally permeable. Albumin then spills into the urine. Nephrotic-range proteinuria is defined as at least 3.5 g of protein in 24 hours or a urine protein-to-creatinine ratio of at least 200 mg/mmol. As albumin leaves the circulation, plasma oncotic pressure falls. Fluid moves into interstitial tissues, producing eyelid, dependent, genital, or generalized edema. The patient may look fluid overloaded while the effective circulating volume is reduced. That apparent contradiction explains why aggressive diuresis can cause hypotension or acute kidney injury. The liver increases production of lipoproteins in response to the altered plasma protein balance, causing hyperlipidaemia. At the same time, urinary loss of antithrombin and other anticoagulant proteins increases the tendency to venous thrombosis. Edema...