lipiduria

Lipiduria is the presence of lipids in the urine. It is most often detected in urine sediment as oval fat bodies and fatty casts, which may appear foamy or be highlighted by lipid-specific stains or polarized light.

Pathophysiology and causes: Lipiduria commonly accompanies nephrotic syndrome, where heavy proteinuria, hypoalbuminemia, and hyperlipidemia disrupt normal glomerular filtration and lipid handling. Lipids can be excreted as cholesterol, triglycerides, and phospholipids, forming lipid droplets within renal tubules or casts. Less commonly, lipiduria can occur with tubular damage or other conditions that cause marked proteinuria or renal lipid accumulation. The presence of lipids in urine reflects a substantial disturbance of renal function rather than a disease by itself.

Detection and interpretation: Routine urinalysis may show lipid-containing material on microscopic examination. The classic finding is oval fat bodies, which are lipid-laden renal tubular cells, often within hyaline or other casts. Under polarized light, cholesterol-containing droplets can display a Maltese cross pattern. Lipids can be demonstrated with special stains such as Sudan III, Sudan IV, or Oil Red O on urine sediment.

Clinical significance: Lipiduria is a useful indicator of significant protein loss and often points to nephrotic-range disease. It is not highly specific for a single disorder but supports the diagnosis of nephrotic syndrome or other severe glomerular pathology when present with appropriate clinical and laboratory findings.

Management generally targets the underlying renal condition (for example, nephrotic syndrome) and may include measures to control edema and lipid levels.