Kidney stones, CKD connection unclear, but clinicians collaborate on treatment
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It did not take long for nephrologist and kidney stone specialist David S. Goldfarb, MD, FASN, to realize that the buildup of pain radiating from the right side of his abdomen was from a kidney stone that had begun its downward migration.
And he came to the realization based on his experience with kidney stones – this was his second one – that the escalating pain meant he did not have the 30 minutes it would take by car to get to his favored hospital and employer, New York University’s Langone Health, for treatment. He told the driver – his wife – to divert to closer-by Columbia-Presbyterian Hospital.
A lithotripsy treatment eventually shattered the 7-mm calcium stone.
Goldfarb, a professor of medicine and physiology at New York University’s Grossman School of Medicine and the clinical chief of nephrology and director of the Kidney Stone Prevention Program at Langone, has a picture of the shattered fragments from the stone on his business card. He received the Oxalosis and Hyperoxaluria Foundation’s Stone Crusher of the Year Award in 2014 based on his professional and personal experience with kidney stones.
“I had been working out after a knee injury and was in fantastic shape,” Goldfarb told Nephrology News & Issues in describing the root cause of his second stone. “I was not drinking enough fluids. It was that simple.”
Stone formation, treatment
There are five types of kidney stones (see table), and treatment options depend on the size and type of stone, Alan C. Pao, MD, co-director of the Stanford Kidney Stone Center and assistant professor of medicine and urology at Stanford University School of Medicine, told Nephrology News & Issues.
“If patients have uric acid stones, we first try to dissolve the stone by reducing urinary acidity,” Pao said. “These stones are soft, do not break apart easily, but can dissolve with alkali therapy.
For calcium stones, size and location of the stone will dictate the treatment approach. If the stone is less than 0.5 cm, we usually try medical expulsive therapy – have the patient pass the stone.
“When the stone is 1 cm to 2 cm, the urologist will typically intervene with ureteroscopy,” Pao said. “When the size is greater than 2.5 cm, percutaneous nephrolithotomy is typically done to remove the stone.”
Treatment for existing stones can have two paths: one for stones causing an obstruction and one for stones in the kidney that are not, Goldfarb said. “Urologists tend to treat for obstruction, but many nephrologists like me do help patients try to pass stones,” Goldfarb said. “I promote relaxation, a warm bath and use of non-steroidals.
“In efforts to prevent recurrence, more fluids to increase urine volume are always appropriate,” Goldfarb said. “Dietary modifications do depend on stone composition; more fruits and vegetables, moderate oxalate and a little less animal protein and salt are helpful.”
The risk factors for forming stones are not completely clear, but “certainly being overweight, metabolic syndrome and [diabetes mellitus] DM are risk factors,” Goldfarb told
Nephrology News & Issues. “There may be inflammation in the kidneys caused by crystals, particularly calcium oxalate, or by oxalate itself. There may be nephrocalcinosis to account for some of that reduced GFR.
“Repeated episodes of obstruction and, in some patients, repeated urological interventions may be important.” Goldfarb said.
Kidney stones and CKD
Research continues on whether kidney stones accelerate progression of chronic kidney disease.
“It is still not entirely clear how the presence of urinary stone disease associates with CKD,” Pao told Nephrology News & Issues. “It is likely the confluence of two factors.
“First, there are shared risk factors for cardiovascular disease and urinary stone disease, including type 2 diabetes, gout, high dietary sodium and older age. The cardiovascular risk factors may raise the risk for chronic kidney disease.
“Second, for patients with more extreme urinary stone disease, recurrent obstruction can directly lead to kidney injury and eventual CKD. This is observed more in patients who have clinically silent obstruction. There may also be metabolic factors such as high oxalate production or calcium deposition (nephrocalcinosis) that can directly injure kidney tissue and ultimately reduce kidney function,” Pao said.
Edward R. Gould, MD, assistant professor of medicine and associate vice-chair for clinical quality at Vanderbilt University Medical Center, said the connection between kidney stones and CKD is progressive.
“My experience mirrors the larger body of literature on the topic,” Gould told Nephrology News & Issues. “Certainly, in those patients who have a history of recurrent stones – either due to lifestyle factors or secondary to underlying disorders, such as hyperparathyroidism, renal tubular acidosis, kidney and urinary tract infections, enteric hyperoxaluria, etc. – I have observed progressive CKD, even with maximal medical management.
“I tend to think about this in the same way that I think about recurrent AKI events from any cause and the consequent CKD,” Gould said. “Each event ‘costs’ some amount of nephron mass, which cumulatively can be observed as CKD when the remaining mass is unable to compensate to address that loss.”
Ryan Hsi, MD, FACS, an associate professor in the department of urology at Vanderbilt who works with Gould on kidney stone cases, added: “It is the cumulative obstruction over time injuring that renal unit on top of the impact of comorbidities and age on baseline renal function” that leads to kidney loss, he said.
Preventive measures
Gould said it is common to first see patients with previous kidney stones “who need the most foundational guidance on stone prevention. My approach at the initial visit is to offer advice that is time-tested and almost universally helpful.” That includes the following measures:
- Enhanced hydration habits that target a goal urine output of greater than 2.5 L daily. “The thrust of this advice is to focus on the urine output and less so on the fluid intake,” Gould said. “This is incredibly relevant for folks who work outdoors in southern summers, as volume lost through perspiration is not available for tubular throughflow.”
- Reduced sodium intake: “Dietary sodium intake is lithogenic,” Gould said. “Many of these folks are younger with less advice historically on sodium intake. So offering some thoughts on reducing sodium intake overall can be helpful.”
- Reduced animal protein: “One of the more challenging factors to modify, I’m advising reducing animal protein sources to 50 g/day to 60 g/day, recognizing my patients may take time to actualize that change.”
“The other thing that nephrology commonly adds to this equation is consideration of and evaluation for those more obscure stone causes,” Gould said. “My initial visit includes a review for medical causes of kidney stones, looking at medication use (both prescribed and supplements), endocrine disorders and comorbidities, as well as metabolic testing to diagnose such problems. Commonly, that includes both serum studies and 24-hour urine analysis.
“We also recommend dietary or nutritional counseling,” Gould said. “I try to get recurrent stone formers to see our renal dietitian for a dietary diary review to correspond with our second visit.”
Alternative methods
Goldfarb, with support from NYU Langone research funds, has developed a drinkable solution that reportedly boosts the level of citate. In an abstract presented at the American Urologic Association Annual Meeting in 2021, Lama Nazzal, MD, and colleagues, including Goldfarb, discussed results from using Moonstone, a high citrate, over-the-counter beverage designed to prevent recurrent kidney stones.
Patients mixed one packet of powder in water and drank it twice a day for 1 week. “We compared 24[-hour] urine chemistry to the result of a similar amount of water only,” the researchers wrote.
The results showed that, compared with water, Moonstone caused an increase in 24-hour urine citrate (from 469.1 mg/day + 231.9 mg/day to 635.4 mg/day + 349.1 mg/day). The 24-hour urine pH increased from 6.21 + 0.78 to 6.61 + 0.69.
“[Two] packets of Moonstone caused increases in 24[-hour] urine citrate and urine pH ... 60 meq of K-Mg-citrate ... was associated with an 85% reduction in kidney stone recurrence in 3 years in patients with calcium stones,” the researchers wrote. “The effect on pH would also be expected to benefit patients with uric acid and cystine stones. Patients preferred Moonstone as a stone prevention.”
- Reference:
- Nazzal L, et al. Poster 21-6420. Presented at: American Urological Association Annual Meeting; Sept. 10-12, 2021; Las Vegas.
- For more information:
- David S. Goldfarb, MD, FASN, can be reached at dsgold@verizon.net.
- Edward R. Gould, MD, FASN, can be reached at edward.r.gould@vumc.org.
- Ryan Hsi, MD, FACS, can be reached at ryan.hsi@vumc.org.
- Alan C. Pao, MD, can be reached at paoman@stanford.edu.
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