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Kidney stone basics, including some ways to avoid them


Often described as the worst pain imaginable aside from child birth, kidney stones can seemingly happen to anyone. But what is a kidney stone? How is it formed? Is passing one as painful as they say? More importantly, is there any way to prevent kidney stone altogether?

Joining us on “Take Care” to talk about the basics of kidney stones and how to prevent them is Dr. Glenn Preminger. Preminger is a professor of surgery and chief of the division of urology at Duke University.

Kidney stones are made of up crystals that form in the, you guessed it, kidney. If enough of these crystals are present, they can come together to form a hard stone. This stone stays in the hollow portion (also known as the collecting portion) of the kidney.

The size of a kidney stone can vary greatly. Generally, they start small but can grow large in size – to three or four inches. Even a small stone can cause significant discomfort when it passes, essentially getting stuck in the kidney tube or ureter.

There are three major types of kidney stones. The most common type of stone is a calcium stone, caused by excessive amounts of calcium in the urine. About 80 percent of people will make calcium stones. There are also stones made of uric acid (a waste product excreted in urine). There are also more rare stones, like cystine stones.

Risks of kidney stone formation

There is evidence to suggest that changes in diet and lifestyle have increased the average person’s risk of developing a kidney stone.

“In the past, say 20 or 30 years ago, it was estimated that about one in 20 people would make a kidney stone in their lifetime … over the last say 30 years there has been evidence to suggest that kidney stones, at least in the U.S., are much more common,” Preminger says. “About one in 11 patients will form a kidney stone over their lifetime, or at least have the risk of forming a kidney stone.”

Preminger says that this nearly doubled risk for kidney stones may be due to changes in both diet and lifestyle. Kidney stones are also genetic. If you have a parent or sibling who forms stone, you are at an increased risk of developing them. He does believe that it’s more likely lifestyle has had a role in increasing the general populations risk for stones, though.

“It’s the high carbohydrate … it’s the high salt diet that many of us eat in the U.S. -- the so-called fast food diet of substances that have a lot of salt or carbohydrates,” Preminger explains. “Also, there are a lot of studies to suggest that people who are overweight or people who have diabetes are at a significantly higher risk for kidney stones than people of normal weight or [who] don’t have diabetes.”

But even thin people with diabetes have increased risk for kidney stones, according to Preminger, but ultimately increased weight does seem to equate to an increase in risk.

Passing the stone

Small stones, especially less than an eighth of an inch, will often pass on their own – sometimes without much discomfort at all. Stones that cause blockage of the ureter are the ones that also cause pain. If the stone doesn’t cause blockage or infection, a patient may not even realize they have kidney stones at all.

The acuity of the obstruction of the urinary tract is thought to cause the pain.

“If you have a small stone, say five or six millimeters in diameter … that rapidly falls from the kidney into the ureter, into the kidney tube, and causes a very quick blockage -- that’s the type of pain where the patient has what we call renal colic,” Preminger says.

Renal colic is pain accompanied by nausea, vomited and pain that is almost unimaginable and described as worse than delivering a baby. Slower obstruction, over weeks or months, can cause much less severe symptoms.


The process of diagnosis usually involves imaging, but if one is seen in the emergency department, a CT scan is the most reliable and sensitive way to diagnose a stone. Depending on the diagnosis (primarily the size of the stone), a recommendation can be made to either pass the stone spontaneously or with a surgical procedure.

There are many surgical procedures that are minimally invasive or even noninvasive, like shock wave lithotripsy. Shock wave lithotripsy is a common procedure that uses sound waves to break the stones into much smaller, passable pieces (like sand). Unfortunately, this procedure does not work for all stones. Endoscopic approaches usually work for any other stones and are performed as outpatient procedures.