There are some cases, though, where the cause of kidney stones remains a mystery. Just ask Kate Mercier, who was first diagnosed with them at age 8 and has been through at least 12 operations related to her stones.
The 17-year-old high school senior in a suburb south of Boston still might not know exactly why she's so prone to forming kidney stones, but all the X-rays, CT scans and ultrasounds she's been through in her young life have helped her choose a career path. She's off to college next year to study radiology, where she might have an edge on her classmates because of her firsthand familiarity with the procedures -- and plenty of compassion for the patients.
Although Mercier's been through a lot of surgeries for her kidney stones, she said, "I've never had pain. I have twinges from time to time, but they almost feel like muscle contractions."
In her case, there is a family history: Both her father and her aunt have had kidney stones. But each of them had only one stone, whereas Mercier tends to form clusters of them. And while she said, "I'll probably have them my whole life," she hasn't let them stop her from doing things -- including earning a brown belt in karate.
Dr. Caleb Nelson, a urologist and co-director of the pediatric kidney stone clinic at Children's Hospital in Boston, said he also thinks the number of children with kidney stones is growing -- though he said the reasons for this are not entirely known.
"It's not simply that we're finding more of them because imaging is picking them up," he said. "We're seeing more kids come in with stone-related symptoms."
Physicians believe, however, that the two main contributors appear to be poor fluid intake and too much dietary salt -- mainly from processed, canned, boxed and junk foods.
The most common symptom of a kidney stone in a child is blood in the urine, said Dr. Bruce Slaughenhoupt, co-director of pediatric urology and the pediatric kidney stone clinic at the University of Wisconsin in Madison. "This is a more common complaint than pain, perhaps because younger kids might have difficulty expressing their pain."
A younger child is also more apt to say they have a tummy ache, likely with nausea and vomiting, while older children can verbalize if their pain is in the lower back or on their side.
Surprisingly, the size of a kidney stone makes no difference to pain levels, explained Slaughenhoupt. "The pain occurs when the stone gets stuck and blocks the ureters. This blockage creates pressure, and pressure is what causes pain."
While kidney stones are nearly painless for some people, Milliner said, others describe it as the worst pain they have ever felt.
"I know some women who have gone through childbirth and also passed a kidney stone, and they say passing the stone was much worse," Nelson said.
Fortunately, most people can take steps to avoid kidney stone formation. Pope tells his patients that a good rule of thumb is to drink half your body weight in ounces of water per day. And he also tells them to check the color of their urine for an indication as to whether they're getting enough liquids. If the urine is dark yellow or brownish in color, then it's too concentrated.
"The key is to keep urine diluted," Pope said.