Urine - Fatty Casts & Droplets

Function

The detection of fatty casts and lipid droplets in urine is a specific microscopic finding known as 'lipiduria.' Fatty casts are formed when fat droplets (cholesterol or triglycerides) are incorporated into a protein matrix (Tamm-Horsfall protein) within the renal tubules. Under a polarized microscope, these lipids often display a characteristic 'Maltese Cross' appearance.

Why it is Ordered

This test is ordered when a physician suspects glomerular disease. It is a hallmark finding in patients presenting with heavy proteinuria (excessive protein in the urine). It helps differentiate between different types of kidney disease, specifically pointing toward those that cause significant damage to the glomerular filtration barrier.

Associated Conditions

• Nephrotic Syndrome: The most common cause, characterized by high protein loss, low blood albumin, and high cholesterol.
• Minimal Change Disease: A common cause of nephrotic syndrome in children.
• Membranous Nephropathy: A leading cause of nephrotic syndrome in adults.
• Diabetic Nephropathy: Advanced kidney damage due to long-standing diabetes.
• Fat Embolism Syndrome: Rarely, fatty droplets may appear after major bone fractures.