II. Epidemiology
- Represents 10% of Kidney Stones
- Occurs in 10-25% of gout patients
- Even higher risk with increasing Uric Acid levels (e.g. 50% Prevalence in those with Uric Acid >13 mg/dl)
III. Evaluation
- See Nephrolithiasis
IV. Types
- Pure Uric Acid Calculi
- Mixed Calcium and Uric Acid Calculi
V. Causes
- Primary cause
- Acidic urine (pH <5.5)
- Other causes
- Gouty Arthritis (confers 2 fold risk of calculi)
- Excessive dietary Purine intake (meats)
- End Ileostomy
- Insulin Resistance
- Results in impaired ammonia and citrate excretion
- Results in lower pH and increased urinary ammonia
- Increased Uric Acid crystallization
VII. Imaging
- See Nephrolithiasis Imaging
- Limited Ultrasound for Acute Renal Colic
- Non-contrast Abdominal CT
- XRay Abdomen
VIII. Management: Prevention of Uric Acid stone recurrence
-
General
- Restrict dietary intake of Sodium and Protein
- Maintain Urine Output: over 2.5 liters per day
- Alkalinize urine (especially if Urine pH is low, acidic)
- Maintain Urine pH >5.5 (6.5 - 7.0 preferred)
- Potassium Citrate 10-20 mEq orally three times daily with meals (preferred) OR
- Calcium Citrate 500 mg, two tablets daily with meals OR
- Sodium Bicarbonate 650 mg tablets (7.74 meq each) two tablets orally three times daily
- Hyperuricosuria (>800 mg/day)
- Potassium citrate as above
- Allopurinol 100-300 mg/day
- Purine (Protein) restriction
- Reduce Urine Uric Acid excretion
IX. References
- Mobley (Feb 1999) Hospital Medicine, p. 21-38
- Goldfarb (1999) Am Fam Physician 60(8): 2269-76 [PubMed]
- Houshiar (1996) Postgrad Med 100(4): 131-8 [PubMed]
- Frassetto (2011) Am Fam Physician 84(11): 1234-42 [PubMed]
- Pietrow (2006) Am fam Physician 74(1): 86-94 [PubMed]
- Preminger (2007) J Urol 178(6): 2418-34 [PubMed]
- Portis (2001) Am Fam Physician 63(7):1329-38 [PubMed]
- Segura (1997) J Urol 158:1915-21 [PubMed]
- Shekarriz (2002) J Urol 168:1307-14 [PubMed]
- Teichman (2004) N Engl J Med 350:684-93 [PubMed]
- Trivedi (1996) Postgrad Med, 100(6): 63-78 [PubMed]