Background
- Also known as kidney stones or renal stones
- 10% lifetime prevalence in men, 5% in women
Stone Types
Stone | % | Composition | Risk Factors |
---|---|---|---|
Calcium oxalate | 75% | calcium oxalate monohydrate, or calcium oxalate dihydrate | usually in acidic urine; hyperparathyroidism, hypercalciuria, hyperoxaluria, hypomagnesemia, and hypocitraturia |
Calcium phosphate | 10% | calcium phosphate, including apatite and brushite | usually in alkaline urine; hyperparathyroidism, renal tubular acidosis |
Uric acid | 10% | uric acid | only in acidic urine, pH <5.5; associated with purine-rich food intake (fish, legumes, meat), gout, and cancer |
Struvite | <10% | calcium, ammonium, and magnesium phosphate | usually in alkaline urine; caused by gram-negative urease-producing bacteria, including Pseudomonas, Proteus, and Klebsiella (but not Escherichia coli) |
Cystine | <5% | cystine | from intrinsic metabolic defect that lead to decreased reabsorption of cystine, lysine, ornithine, and arginine in the renal tubules |
Pathophysiology
- Varies by stone type
- Low urine output/poor oral intake
- Increased uric acid, which precipitates in low pH
- Low pH, which precipitates animal protein
- Hypercalciuria
- Genetic (familial)
- Hypercalcemia: hyperparathyroidism, vitamin D
- Increased oxalate
- Genetic
- Diet: nuts, greens, chocolate, etc.
- IBD: fatty acids bind to calcium in gut, allowing oxalate absorbtion
- Malabsorption
- Vitamin C
- Decreased citrate (i.e. 3 bicarbs), e.g. from RTA
- Increased phosphate, e.g. from carbonated beverages, which precipitates in high pH
- Urinary tract infection caused by urease-positive bacteria, leading to struvite stones
- Urinary stasis, e.g. in polycystic kidney disease, medullary sponge kidney
- Medications, including atazanavir and other HIV medications, guiafenesin, indinavir, sulfonamides, and triamterene
Clinical Manifestations
- Common cause of hematuria and abdominal, flank, or groin pain
Investigations
- Dietary assessment
- Electrolytes (especially for K and HCO3), calcium profile, PTH, urinalysis, urine microscopy
- 24h urine collection, sent for
- volume
- creatinine, CrCl
- Na, K, urea
- calcium
- oxalate
- uric acid
- phosphate
- spot test for cystine
- citrate and magnesium in a separate collection
Management
- Imaging
- Stone diet
- Maintain urine output 2L/d
- Low salt
- Normal calcium
- Increased fruit and vegetables
- Moderate meat and alcohol
- Potassium citrate 20mEq BID, to increased citrate and pH of the urine
- Hydrochlorothiazide, to decrease urine calcium
- Allopurinol, to decrease urine urate