AUA Kidney Stone Guidelines Unveiled

ORLANDO - The American Urological Association (AUA) announced at its annual meeting the development of its first guidelines for the medical management of kidney stones.

Margaret S. Pearle, MD, PhD, who chaired the panel that reviewed the available evidence that formed the basis of the guidelines, summarized the recommendations in a presentation at the AUA's 2014 annual meeting.

In discussing the rationale for the new guidelines, Dr. Pearle noted that kidney stones are a common problem with a high rate of recurrence, and despite effective and established treatment regimens for medical management, evidence suggests that medical management is underused. Additionally, she said, management of patients with recurrent stones lacks uniformity.

The guidelines contain 27 statements that fall broadly into the categories of evaluation, diet therapies, pharmacologic therapies, and follow-up. All patients diagnosed with a stone should have a screening evaluation that consists of dietary intake, medical therapies, serum chemistries, urinalysis, and urine culture, said Dr. Pearle, professor of urology and internal medicine at the University of Texas Southwestern Medical Center in Dallas. The evaluation is aimed at identifying medical conditions associated with stone formation, such as primary hyperparathyroidism or type 2 diabetes, dietary aberrations, such as low or high calcium intake or excessive intake of animal protein, or medications such as topiramate, she told listeners.

Serum chemistries should be obtained to define underlying conditions that may be associated with recurrent stones, such as primary hyperparathyroidism or distal renal tubule acidosis. Measuring serum parathyroid hormone is considered an optional study that should be obtained only if primary hyperparathyroidism is suspected, Dr. Pearle said.

In addition, Dr. Pearle stated that “a stone analysis should be obtained at least once if a stone is available because knowledge of stone composition can implicate certain underlying etiologies, such as a low urine pH in patients with uric acid stones.”

Metabolic testing should be performed in high-risk or interested first-time stone formers as well as in recurrent stone formers, she said. Metabolic testing should consist of one or preferably two 24-hour urine collections obtained under random diet. These urine collections should be analyzed for total volume, pH, calcium, oxalate, uric acid, citrate, sodium, potassium, and creatinine. “The 24-hour urine is then used to guide recommendations regarding dietary measures and medication.”

The guidelines also recommend that:

• All stone formers should be advised to drink enough fluids to achieve a urine volume of at least 2.5 liters daily.
  
• Patients with calcium stones and high urinary calcium should be advised to limit their sodium intake and to consume the recommended daily allowance of calcium of 1,000 to 1,200 mg daily.
• Patients with uric acid stones and calcium stones and high urinary uric acid should be advised to limit their intake of non-dairy animal protein. About 30% of urinary uric acid is derived from dietary purine intake, and animal protein accounts for most purine intake, Dr. Pearle noted.
  
• Patients with high urinary calcium and recurrent calcium stones should be offered thiazide diuretics because these medications act directly on the distal renal tubule and indirectly at the proximal renal tubule to promote renal calcium reabsorption.
  
• Patients with recurrent calcium stones and low urinary citrate should be offered potassium citrate because this medication provides an alkali load that promotes a citraturic response and increases urinary inhibitory activity.
  
• Patients with recurrent calcium stones and who have hyperuricosuria should be offered allopurinol.
  
• Thiazide diuretics and/or potassium citrate should be offered to patients with recurrent calcium stones in whom no metabolic abnormality is identified or in whom appropriate metabolic abnormalities have been addressed but stone formation persists.
  
• Allopurinol should not routinely be offered as first-line therapy to patients with uric acid stones. Uric acid nephrolithiasis is primarily a disease of urinary acidification, and at a pH greater than 6 to 6.5, most uric acid will be found in its soluble or undissociated form, and even high amounts of uric acid at these higher urinary pHs will be fully solublized, Dr. Pearle explained.

Dr. Pearle concluded her talk by mentioning the importance of follow-up. “Success in gauged by improvement in urinary stone risk factors and ultimately by reduction in stone formation,” she said. Serial urine collections must be obtained to address changes in urinary risk factors.

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