You’ve probably heard that passing a kidney stone can be very painful, but you might not know exactly what they are or how to avoid one in the first place.
Kidney stones — and passing a kidney stone, in particular — are notorious for being painful. They’re also surprisingly common. In fact, 11% of men and 6% of women in the United States will have a kidney stone at least once in their lifetime.
While kidney stone pain is unmistakable, it’s also possible to have a kidney stone and not even know it. If the stone is small enough to pass through your urinary tract, it may cause little to no pain at all; but if it’s large and gets stuck, you may have severe pain and bleeding.
Kidney stones that cause symptoms or cannot pass on their own need to be treated by a medical professional.
What are kidney stones?
The kidneys — two bean-shaped organs located just below the rib cage on each side of the spine — filter waste and extra water from the bloodstream to create urine. From the kidneys, urine then moves through two thin tubes, called ureters, into the bladder.
In addition to filtering waste, the kidneys also regulate water, salt and mineral levels in your blood. Renal calculi, the medical term for kidney stones, form when there is a high level of these minerals in the urine.
“When stone-forming substances — most commonly calcium and oxalate — oversaturate your urine, crystallization can occur, and kidney stones can begin to form,” explains Eric L. Kau, MD, a urologist at Keck Medicine of USC and clinical assistant professor of urology at the Keck School of Medicine of USC. The crystals can harden together in masses of varying shapes and sizes.
Are there different types of kidney stones?
Kidney stones can range in size and shape, with some as small as a grain of sand, others the size of a pebble and less commonly, some growing as large as a golf ball. Kidney stones can also be made of different substances, and they are divided into four common types.
The types of kidney stones are:
- Calcium stones — The most common kidney stone, it includes calcium oxalate and calcium phosphate stones.
- Uric acid stones — Another common kidney stone, it may form due to elevated levels of uric acid in the urine. “Elevated uric acid in urine can be related to a diet high in animal proteins, such as beef, chicken, pork and fish,” Kau says.
- Struvite stones — These less common stones tend to form after a urinary tract infection. They are also prone to developing suddenly and may grow quickly.
- Cystine stones — These stones form in people with cystinuria, an inherited condition that causes the buildup of the amino acid cystine in the kidneys and bladder.
What causes kidney stones?
Several factors are associated with the formation of kidney stones, including family history, low urine volume, diet and weight, and certain medical conditions and medications. In general, if your parents had kidney stones, you’re more likely to have them, as well. They’re more prevalent in men than in women, and once you’ve had a kidney stone, your risk goes up of having another.
Lifestyle factors may also increase your risk of getting kidney stones. To lower your chance of developing kidney stones, it’s best to avoid dehydration, which can cause low urine volume. In fact, if you don’t drink enough fluids — especially water — your urine can become too concentrated, increasing the chances of stones forming.
“Having decreased urine volume provides a more favorable environment for kidney stone formation,” Kau explains.
Be sure to stay hydrated, particularly when it’s hot out or when you’re sweating a lot, such as during exercise.
In addition, too much salt, processed meats or animal protein in your diet may also elevate your risk of developing kidney stones.
“Having too little or too much calcium in your diet may increase your risk for calcium oxalate stones,” Kau adds.
Obesity, being overweight and bowel conditions, like Crohn’s disease or ulcerative colitis, may also increase your chances of getting kidney stones.
What are the symptoms of kidney stones?
Although passing a kidney stone tends to be linked to acute pain, the general symptoms for kidney stones depend on a few factors, including the size and location of the stone itself.
“A kidney stone that remains in the kidney and does not cause urinary obstruction typically does not cause pain,” Kau explains. “Often, these stones are incidentally found on imaging studies, such as ultrasound or CT scan, for another issue.”
“Other kidney stones may pass through the urinary tract system with little or no discomfort at all,” Kau adds.
The acute pain commonly associated with passing a kidney stone is just one of several symptoms a patient may experience, when a stone becomes lodged and blocks urine flow.
“When a kidney stone passes from a kidney into the ureter, the small tube that connects a kidney to the bladder, it can lead to obstruction of urine flow, which can cause pain,” Kau says. “This pain can be located in your back, side, lower abdomen or groin and may shift, as the stone moves through the ureter. It can range from being mild to severe and can be intermittent in nature.”
Other symptoms may include nausea and vomiting, blood in the urine, urinary urgency or pain upon urination.
“In cases where there is an infection, you may have fever and chills,” Kau adds.
It’s important to see a medical professional, if you experience these symptoms.
How long does it take to pass a stone?
The time to pass a kidney stone is highly variable and depends on the size and location of the stone itself, according to Kau.
“Having a smaller stone (less than 4 millimeters in size) and having a stone lower in the ureter (closer to the bladder) are two factors that improve the chance of passing a kidney stone,” he explains.
What are the treatment options for kidney stones?
Treatment for kidney stones will depend on the type, size and location of the stone. Lab tests and imaging studies can help your doctor reach a diagnosis, determine if it’s feasible to wait for the stone to pass on its own and chart a treatment course that’s right for you.
“If conservative management with pain medication, hydration and/or a medication that may help facilitate stone passage is not successful, surgical intervention may be necessary,” Kau says.
If a stone cannot pass on its own, the type of procedure used to treat it will also depend on its size and location. Kau notes that three of the most common options are:
- Ureteroscopy. This procedure is used to treat kidney stones located in a kidney or ureter. Physicians use a small scope to pinpoint the location of the stones and assess if they can be removed using a basket-like instrument. If a stone is too large, it may be fragmented using a laser, and the smaller pieces are subsequently removed. This procedure does not require incisions and is typically performed in the hospital with anesthesia. The majority of patients go home on the same day.
- Shock wave lithotripsy. This procedure employs shock waves, guided by X-ray or ultrasound, to break up kidney stones into smaller fragments, which then pass out of the body through the urine. According to Kau, patients receive anesthesia and go home on the same day.
- Percutaneous nephrolithotomy. This option is typically used to treat larger stones in the kidney. A small incision is made in a patient’s back, establishing a tract that allows a scope to pass into the kidney. Another instrument is then used to fragment the stone and remove the pieces. A patient may be hospitalized overnight or for a few days.
After surgery — or after you pass the stone, if you’re able to collect part of it — your doctor will test the stone to determine the type it is to help advise you on how to avoid them in the future.