UROLITHIASIS
80% of stones are composed of calcium oxalate or phosphate.
Others include uric acid (9%), struvite (10%), & cystine (1%) stones.
Struvite stones can form into a staghorn or large calculus that overwhelms the
renal collecting system; are Mg ammonium phosphate; secondary to elevated urine
pH, & urease forming Proteus or Klebsiella species.
Urea breakdown yields ammonia as a by-product, which increases the urinary pH (typically to more than 8), and facilitates struvite stone formation.
Uric acid stone formation is related to low urinary uric acid levels, low urine pH, and low urinary volume. Most commonly, these patients will present as idiopathic uric acid stone formers; however, metabolic disorders such as diabetes and obesity will also increase the risk of uric acid stones.
Cystine stones are rare and occur due to an inborn congenital disorder causing mutations in 2 genes, SLC3A1, and SLC7A9. These mutations cause defective cystine metabolism and transport, resulting in cystinuria and stones.
Satyendra Dhar MD,
