URINE GLYCOSAMINOGLYCANS

A glycosaminoglycan (GAG) urine test measures levels of mucopolysaccharides excreted in urine to screen for and monitor mucopolysaccharide storage disorders (mucopolysaccharidoses). It can be qualitative or quantitative (often normalized to creatinine) and is used when developmental delay, organomegaly, or skeletal abnormalities suggest a lysosomal enzyme deficiency. Elevated urinary GAGs prompt confirmatory enzyme and genetic testing.

Glycosaminoglycans (GAGs) form a negatively charged mucous layer on the bladder and urinary tract lining that repels bacteria and irritants, preserves epithelial barrier function and impermeability to solutes, and retains water for lubrication. They modulate inflammation and aid mucosal repair, reducing infection risk and tissue damage while maintaining bladder elasticity and protective coating integrity.

The four major glycosaminoglycans are hyaluronic acid (hyaluronan), chondroitin sulfate (with dermatan sulfate as a related variant), heparan sulfate (and its anticoagulant form heparin), and keratan sulfate. These long unbranched polysaccharides differ in repeating disaccharide units and sulfation patterns, contributing to extracellular matrix structure, hydration, lubrication, and tissue repair functions.

A urine GAG test measures glycosaminoglycans excreted in urine to screen for mucopolysaccharidoses—genetic lysosomal enzyme disorders that cause excess GAG accumulation. It quantifies total urinary GAGs and may use electrophoresis to identify specific GAG types. Elevated levels suggest MPS and prompt enzyme assays or genetic testing for diagnosis and management. It’s a screening, not definitive, test.

A urinogram is a comprehensive urine examination assessing physical, chemical and microscopic features to evaluate kidney function, urinary tract infections, metabolic disorders and systemic diseases. It typically includes dipstick testing for pH, protein, glucose, blood, nitrites and leukocyte esterase, plus microscopic analysis for cells, casts and crystals. Variants include spot tests and 24-hour collections for quantitative measurements.

The urine myoglobin test detects myoglobin in urine to identify muscle breakdown (rhabdomyolysis) or severe muscle injury. It helps explain dark urine and unexplained muscle pain or weakness, assesses severity of muscle damage, and monitors the risk of acute kidney injury. Results guide prompt treatment—such as IV fluids—and ongoing monitoring to prevent or manage renal complications.