|Brian Matlaga, MD|
EVALUATIONAll patients with a newly diagnosed stone should undergo a screening evaluation.
This should include a dietary and medical history, serum chemistry evaluation, urinalysis and urine culture, and a stone analysis.
Important aspects of the medical history include signs, symptoms and comorbidities associated with stone disease (renal tubular acidosis, primary hyperparathyroidism, diabetes, gout, obesity); a dietary history (fluid, calcium, protein and fruit/vegetable intake); and pertinent medications (topiramate, zonisamide, acetazolamide, triamterene, probenecid, protease inhibitors, vitamin C).
When examining a serum chemistry:
- high calcium and low phosphate can indicate primary hyperparathyroidism
- a serum parathyroid hormone level should be checked only if primary parathyroidism is suspected
- low bicarbonate, low potassium and increased chloride may indicate distal renal tubular acidosis
- increased uric acid can indicate low pH or hyperuricosuria
- cystine stones indicate cystinuria
- uric acid stones identify low urinary pH as a target for treatment
- struvite stones may coincide with recurrent urinary tract infections
- Family history
- GI disease/bowel resection
- Type II diabetes mellitus
- Distal renal tubular acidosis
- Primary hyperparathyroidism
- Recurrent urinary tract infections
- Children or adolescents
- Solitary kidney
- increase fluid intake to achieve a urine volume of 2.5L each day.
- limit sodium intake
- consume 1000-1200 mg/day of dietary calcium [2,3]
PHARMACOLOGIC THERAPIESThiazide diuretics should be offered to patients with high or relatively high urinary calcium and recurrent calcium stones.
Potassium citrate should be offered to all patients with recurrent calcium stones and low urinary citrate.
Thiazide diuretics and/or potassium citrate should be offered to patients with recurrent calcium stones and no other identifiable metabolic abnormalities.
Allopurinol should be offered to patients with recurrent calcium oxalate stones, hyperuricosuria and normal urinary calcium. Allopurinol should not be offered as first-line therapy to patients with uric acid stones, rather treatments to alter urinary pH should be considered.
FOLLOW-UPUrinary parameters are believed to precede stone recurrence, therefore serial urine collections should be obtained to assess changes in stone risk factors. Success of any treatment should therefore be gauged by improvement in urinary risk factors and ultimately into reduction in stone events.
 Parks et al, KI 51: 894, 1997