 |
| Brian Matlaga, MD |
EVALUATION
All 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
A stone analysis should be obtained at least once for a patient with stones:
- 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
24-hour metabolic testing should be completed in high-risk patients, interested first-time stone formers and recurrent stone formers. This is based on data that supersaturation levels in 24-hour urinalyses consistently reflect stone composition and preventive treatments can result in reduction of supersaturation levels in most patients.[1]
"High-risk" stone formers include those with:
- Family history
- GI disease/bowel resection
- Gout
- Type II diabetes mellitus
- Obesity
- Distal renal tubular acidosis
- Primary hyperparathyroidism
- Nephrocalcinosis
- Recurrent urinary tract infections
- Children or adolescents
- Solitary kidney
DIET THERAPIES
Clinicians should recommend that all stone formers:
- 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]
Patients with uric acid stones, or calcium stones with high urinary uric acid, should limit intake of animal protein.
PHARMACOLOGIC THERAPIES
Thiazide diuretics should be offered to patients with high or relatively high urinary calcium and recurrent calcium stones.[4]Potassium citrate should be offered to all patients with recurrent calcium stones and low urinary citrate.[5]
Thiazide diuretics and/or potassium citrate should be offered to patients with recurrent calcium stones and no other identifiable metabolic abnormalities.[6]
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-UP
Urinary 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.-----
This blog entry was extracted from a recent presentation by Brian Matlaga, MD, the AUA GUIDELINES FOR THE MEDICAL MANAGEMENT OF KIDNEY STONES. The Guideline Committee was led by Margaret S. Pearle, MD, PhD, Chair, and David S. Goldfarb, MD, Vice-chair. To read the entire Guideline Document click on the link above or here.
-----
[1] Parks et al, KI 51: 894, 1997
[2] Borghi et al, J Urol 155: 839, 1996
[3] Borghi et al, NEJM 346:77, 2002
[4] Pearle, Roehrborn et al, J Endourol 13, 1999
[5] Barcelo et al, J Urol 150: 1761, 1993
[6] Ettinger et al, J Urol 158: 2069, 1997