Types of Stones
incidence of uric acid calculi is approximately 5% - 10% of all
renal stones. Men are affected four times more often than women.
Approximately 25% of patients with gout will form uric acid stones.
However, the majority of patients who form uric acid calculi have
no detectable abnormalities in uric acid metabolism.
that may contribute or predispose to uric acid stone formation include
acidic or strongly concentrated urine, excess urinary excretion
of uric acid, distal small bowel disease or resection (regional
enteritis), ileostomies, myeloproliferative disorders being treated
with chemotherapy and inadequate caloric or fluid intake. Treatment
is tailored toward increasing urine volume and urinary pH. If hyperuricosuria
is present, it can be corrected with appropriate dietary management
and/or administration of allopurinol, a xanthine oxidase inhibitor.
Unlike most other renal calculi, existing uric acid stones can often
be dissolved with either systemic or topical alkalinizing agents.
Produced in acidic urine (pH <5.5)
Amenable to medical therapy
Pathophysiological factors: anemia, neoplastic disorders, intoxication,
cardiac infarction, irradiation and treatment with cytotoxic agents.
Metabolic abnormalities: primary gout, Lesch-Nyhan syndrome.
Pharmacologic influence on the excretion of uric acid: uricosuric
agents (probenecid, sulfinpyrazone, salycilates), diuretics (thiazide,
furosemide) and analgesics, vitamin C.
In contrast to other types of stones, medical therapy is the mainstay
of treatment and prophylaxis. Treatment includes hydration, and
limitation of dietary sodium (<150 meq/day) and protein intake.
Potassium citrate at a dose titrated to alkalinize the urine to
a pH of 6-7 will dissolve uric acid stones.
Low RK, Stoller ML. Uric acid-related nephrolithiasis. Urol Clin
North Am 1997, 24:1:135-148.