Oxalate is an end product of glycolate and glyoxalate metabolism. Humans have no enzyme capable of degrading oxalate, so it must be eliminated by the kidney. In tubular fluid, oxalate can combine with calcium to form calcium oxalate stones. Increased urinary oxalate excretion promotes calcium oxalate stone formation. Causes of hyperoxaluria include inherited enzyme deficiencies (primary hyperoxaluria), gastrointestinal disorders associated with fat malabsorption (secondary hyperoxaluria) and increased intake of oxalate-rich foods.
24 hour urine collection acidified or
fresh random urine is suitable if acidified promptly on receipt in the laboratory or
EDTA (lavender top) on ice rush to laboratory
24 hour urine collection
Random urine: 8 mL (pH <4.0)
or 1 mL plasma
Up to 6 weeks
Not currently performed in house; this is a referred test.
Urine oxalate is preferred specimen type when renal function is normal.