Urinary grit

Specialty: Nephrology and urology.

• grit in urine
• microlithiasis passage
• urinary sandstone

Why it occurs

• Hyperuricosuria with uric acid precipitation (high urinary excretion of uric acid, favored by persistently acidic urinary pH <5.5, which generates visible amorphous crystals like orange or brick-colored grit)
• Hypercalciuria or hyperoxaluria (precipitation of calcium oxalate salts in concentrated urine, forming tiny crystals that group together simulating grains of sand)
• Cistinuaria (congenital error in the transport of dibasic amino acids that excretes cystine, precipitating typical hexagonal crystals such as whitish grit)
• Severe chronic dehydration (low intake of free water supersaturates urinary mineral salts, facilitating their precipitation)

Initial workup

Chemical and crystallographic analysis of the grit recovered by urine filtration; systematic examination of urine with urinary sediment to identify crystalline morphology under polarized light microscope; 24-hour urine collection for metabolic study (calcium, phosphorus, uric acid, oxalate, citrate, creatinine, cystine); High-resolution renal and urinary tract ultrasound.

Standard management

• Potassium citrate — 10-20 mEq orally 2 to 3 times a day to alkalinize the urine to an optimal pH of 6.2-6.8 in case of uric acid grit, and increase the excretion of citrate, which is a natural inhibitor of calcium oxalate crystallization
• Allopurinol — 100-300 mg daily orally if hyperuricosuria coexists with documented hyperuricemia
• Increase oral water intake massively (to maintain a urinary volume greater than 2.5 liters per day, diluting the solutes in urine).