The root causes of recurrent kidney stones can help physicians determine whether dietary changes or medication will be more helpful for at-risk patients, according to Glenn Preminger, MD, professor of urologic surgery at Duke University in Durham, North Carolina.
For many patients, diet therapy is exceedingly reasonable and enough to correct the underlying problems. However, for patients who do not respond sufficiently to dietary changes, physicians will often prescribe medical therapy, he said during a panel discussion at the virtual American Urological Association 2020 Annual Meeting.
The session — described as a “crossfire” approach — was designed to spur a robust examination of the two options for stone prevention, Preminger, who moderated the session, told Medscape Medical News.
Most important is to start with metabolic evaluation, he said. Two urine samples the patient collects 24 hours apart can provide a sense of the biologic factors contributing to their stones.
“Based on these findings, we can select the most appropriate treatment,” he said.
Stones composed of calcium oxalate or uric acid, for example, might respond to changes in diet. In contrast, for stones linked to findings of absorptive hypercalciuria type I, hypocitraturia, primary hyperoxaluria, or cystinuria, medication might be needed.
We’ve known for decades that diet can control urinary risk factors.
But many patients are averse to taking drugs, particularly those already taking several medications, said Kristina Penniston, PhD, from the Department of Urology at the University of Wisconsin–Madison.
And significant evidence from published studies indicates that changes in diet lessen known risk factors for stones, such as hypercalciuria, hyperoxaluria, and hypocitraturia, she said. “We’ve known for decades that diet can control urinary risk factors.”
Changes in diet also deliver multiple benefits, whereas drugs tend to target single risk factors. An increase in the consumption of fruits and vegetables, for example, results in higher citrate excretion and adds water to the diet. In addition, the increase boosts fiber intake, which provides prebiotics that support bacterial oxalate degradation in the digestive tract.
“By increasing fruits and vegetables — just that one thing — you can manipulate all of these different urinary risk factors. There isn’t a medication that can do that,” said Penniston.
The benefits of nutrition therapy for stone prevention likely have been underestimated because dietary recommendations are not always made in ways that actually help patients change their approach to food, she added. The advice is often not accompanied by clear recommendations about what foods patients need to eat and how much they need to eat.
“It’s like giving a drug without giving a dosage,” she said.
When providing patients with dietary recommendations, Penniston said she uses the same conservative approach she takes with drugs: prescribe in the smallest possible doses.
For hypertension, “typically, at least to start with, the physician selects the single medication — based on available biochemical and other patient-specific indices — that is likely to have a blood-pressure-lowering effect. This is opposed to, for example, prescribing all possible blood pressure medications, which would be unethical,” she told Medscape Medical News.
“Similarly, rather than throwing at a patient every possible dietary recommendation for stone prevention, select the one or two recommendations — again, based on patient-specific factors, such as 24-hour urine measures, comorbidities, stone history, stone composition — that are most likely to address a patient’s stone risk,” she said.
This approach to nutrition requires “diagnostic effort,” said Penniston. A registered dietitian nutritionist should identify which urinary risk factor — hypercalciuria, hyperoxaluria, hypocitraturia — can be controlled with diet.
But, she acknowledged, both dietary changes and medications can help prevent kidney stones.
Most of the research in support of dietary changes stems from studies of risk factors for stones. Only one major randomized trial directly studied whether a specific diet could reduce stones, said David Goldfarb, MD, clinical chief of nephrology at NYU Langone Medical Center in New York City.
That study of 120 men in Italy showed that a low-protein, low-sodium diet led to fewer recurrences of stones than a low-calcium diet.
Medications, especially potassium citrate, and even thiazides, are underprescribed for stone disease, he said.
The drug treatments should not be limited to patients who can do the 24-hour urine-collection tests, said Goldfarb, who was involved in a previous study that assessed the diagnostic benefit of these tests.
Physicians can proceed with prescriptions for these drugs in many cases without first requiring patients to complete additional screening, he said.
“This is particularly important for patients who do not have insurance to pay for 24-hour urine collections, and for people in other countries, where the test may not always be available,” Goldfarb told Medscape Medical News.
American Urological Association (AUA) 2020 Annual Meeting. Presented June 27, 2020.
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