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Although they are both kidney stone specialists, Esteban Emiliani Sanz, MD, PhD, and David S. Goldfarb, MD, have had vastly different career paths. Dr. Emiliani, after practicing in Barcelona for a decade, was appointed chief of endourology at NYU Langone Hospital—Brooklyn in February, joining a ranked No. 2 in the nation by U.S. News & World Report. Dr. Goldfarb, a nephrologist who is clinical chief of the at NYU Grossman School of Medicine, has been a faculty member based in Manhattan for four decades. Dr. Goldfarb, director of the Kidney Stone Prevention Program at NYU Langone Health, has personally experienced three kidney stone episodes, “events that determined my career path.” Dr. Emiliani hasn’t had one and hopes to keep it that way.

What these clinicians share are international reputations in their fields, a highly personalized approach to patient care, and a passion for treating and preventing a condition so vexing and perplexing that it’s cited in the Hippocratic oath. “What we do is not just about removing or preventing stones,” says Dr. Emiliani. “It’s about restoring a person’s sense of normalcy and the freedom to live pain-free.” Here, these experts share their knowledge, experience, and insights on how to alleviate, and avoid, the intense suffering that more than 10 percent of Americans endure at least once in their lifetime. 

Kidney Stones Are Aptly Named

The medical term for a kidney stone is renal calculus, derived from Latin words meaning “kidney pebble.” In most people, natural chemicals in the urine, like citrate, a form of citric acid found in fruits and vegetables, keep stones from forming. For an unlucky few, a high concentration of minerals and salts causes tiny crystals to coalesce into a mass in the kidney.

“There are actually 7 types and 24 subtypes of kidney stones, each requiring its own treatment and prevention plan,” notes Dr. Emiliani. The most common variety is composed of calcium oxalate monohydrate, a hard material that forms when urine contains low levels of citrate and a person’s diet is low in calcium. Uric acid stones, more common in men, tend to occur in people who are obese or have hypertension, diabetes, or metabolic syndrome. Struvite stones, more common in women, result from certain types of urinary tract infections.

“A kidney stone is like an apple that falls from the tree when it’s ripe,” explains Dr. Goldfarb. When a stone leaves the kidney, it moves into the ureter, the narrow tube that connects the kidney to the bladder. If the stone becomes lodged there, the obstruction causes urine to back up, creating pressure on the kidney and surrounding tissue. The pain typically starts in the flank, then radiates into the abdomen and the groin. To expel the intruder, the ureter contracts, squeezing the stone and triggering waves of agony that last from 20 to 60 minutes. The pain is often compared to that of childbirth or a gunshot wound, but Dr. Emiliani ranks the intensity as “above both of these.”

They Are Becoming More Common

The incidence of kidney stones has been on the rise since the 1970s, affecting every age group—from children to people in their 80s—and both sexes. Once you’ve had one, you’re likely to get another; the 5- to 10-year recurrence rate is 50 percent.

Most stones form due to a combination of genetic and environmental factors. “Some people have too much of something that promotes crystallization or too little of something that inhibits it,” explains Dr. Goldfarb, “but we don’t really understand all the genes involved.” Other risk factors have been more clearly identified. Dehydration is a leading culprit, but obesity, high blood pressure, and diabetes have all been shown to increase the risk of a stone. So does a diet rich in animal protein, sodium, and sugars.

Another suspect is antibiotics. These medications alter the bacteria living in the gut, leading to complex changes in urinary chemistry that may increase the likelihood of developing stones. Dr. Goldfarb and nephrologist Lama Nazzal, MD, an expert on the intestinal microbiome’s effect on kidney stone development, published one of the first papers on this topic. “We found that one year after a course of antibiotics, the likelihood of forming a kidney stone was two to three times greater,” he says.

Our Experts Leave No Stone Unturned

A kidney stone will usually pass on its own, but it could take days or even weeks. Stones larger than 5 millimeters may be too big to pass naturally, and some people are in so much distress that they visit one of NYU Langone’s Emergency Departments, in Manhattan and Brooklyn, and onLong Island. At our Brooklyn hospital, Dr. Emiliani and his team—urologists Frederick Gulmi, MD, Valary T. Raup, MD, Paul Guidos, MD, and Jennifer Nauheim, MD—care for 500 patients with kidney stones annually. Their treatment strategy depends on the size and location of the stone, its composition and density, and the patient’s anatomy and personal preference. “We always opt for the least invasive approach possible,” says Dr. Emiliani, “and recent innovations afford us greater precision than ever.”

The presence of a kidney stone is confirmed by symptoms, urine testing, and a CT scan. Depending on the type of stone, alpha blockers can relax the muscles around the ureter, allowing small stones to pass. Potassium citrate may be prescribed to help dissolve uric acid stones or cystine stones, the latter of which stem from a hereditary genetic disorder. The most common therapeutic procedure is a ureteroscopy: a narrow, flexible fiberoptic scope is threaded through the ureter, enabling the surgeon to extract the stone with a tiny basket. For larger stones, a laser is used to “dust,” or pulverize, the stone so that the fragments can be suctioned out. For large, irregularly shaped stones in hard-to-reach areas, the surgeon may need to create a narrow tunnel to the kidney through a small incision in the back, known as percutaneous nephrolithotomy.

“For all procedures, we employ the smallest instruments and most advanced techniques,” says Dr. Emiliani, who earned a doctorate in laser stone treatment from two leading European academies: Paris’s Sorbonne University and the Autonomous University of Barcelona. “These tools enable us to adapt to each patient’s anatomy, reduce the risk of complications, shorten recovery time, and lower the odds of recurrence.”

A Stone Can Be a Blessing in Disguise

Kidney stones are often linked to underlying metabolic abnormalities and health problems, including diabetes, obesity, hypertension, coronary artery disease, and chronic kidney disease. “Kidney stones tend to be a wake-up call,” says Dr. Emiliani.

Patients with recurrent stones are instructed to undergo laboratory analysis of their urine, among other tests. Dr. Emiliani will soon collaborate with colleagues to create an AI model that helps clinicians interpret the results of metabolic evaluations. “The only way to diminish stone formation is to understand whether a metabolic or genetic disorder is the primary cause, learn what the patient’s diet is like, and identify risk factors,” says Dr. Goldfarb.

Prevention Is the Best Medicine

While kidney stones do often reoccur, experts agree that most can be prevented. If the root cause can be identified, a tailored prevention plan can be applied that may include dietary guidance, supplementation, and targeted medications.

Dr. Goldfarb stresses that for all types of kidney stones, “the single most important preventive measure is adequate fluid intake—at least 3 quarts of liquid per day.” Water, coffee, tea (except black tea), and milk are all fine, but sugary soft drinks should be limited, because insulin spikes increase the amount of calcium in urine. The more we sweat, the less urine we produce, so when exercising or engaging in vigorous activities, stay well hydrated, especially on hot, humid days.

Diet plays a critical role. Many foods, including snacks, fast foods, and packaged, processed, or canned foods, are loaded with salt to enhance flavor. More sodium in the urine leads to more calcium as well. You’ll need to be vigilant to achieve the recommended daily intake of less than 2,000 milligrams of sodium. Citrus fruits such as oranges and lemons are a plus in preventing stones because the citrate they add to urine reduces the formation of stones. People who form calcium oxalate stones should limit their intake of black pepper, chocolate, nuts, sweet potatoes, soy products, green leafy vegetables, some berries, and other foods high in oxalates.

It was long thought that dairy promotes calcium stones, but recent studies have overturned that theory. A dairy-rich diet is, in fact, preventive, because calcium binds to oxalate in the intestine, reducing its absorption. Still, Dr. Goldfarb cautions that some calcium supplements, as well as high-dose forms of vitamin C, should be avoided.

Most Americans consume more animal protein than they need. Dr. Goldfarb suggests limiting your daily intake of beef, poultry, pork, and fish to six to eight ounces total per day. “When you eat animal protein you’re taking in amino acids, leading to changes in urine chemistry that can produce calcium and uric acid stones,” Dr. Goldfarb explains. He endorses two highly regarded diets for stone prevention: DASH (Dietary Approaches to Stop Hypertension), emphasizing fruits, vegetables, whole grains, low-fat dairy products, and lean protein; and the Borghi diet, which emphasizes a moderate intake of calcium-rich foods, low sodium, and limited animal protein and oxalate-rich foods.

“The bottom line,” says Dr. Goldfarb, “is if you’ve never had a kidney stone, eat whatever you want. But if you’ve had one or have a family history of stones, watch your diet and keep up your fluid intake.”