Written by Dr. Andrew Siegel:
Kidney stones are a common problem that I treat daily. Kidney stones are often related to our dietary habits, the amount of fluids that we drink, and our weight.
If you have ever suffered with a kidney stone, you know what excruciating pain is. Many women who have experienced both passage of a kidney stone and natural childbirth without any anesthesia will report that the childbirth was the less painful of the two!
Stones are a common condition that have occurred in humans since ancient times — kidney stones have even been found in an Egyptian mummy dated 7000 years old. The good news is that most of them will pass spontaneously without the necessity for surgical intervention. If surgery is required, it is minimally invasive (open surgery for kidney stones has virtually gone by the wayside).
How do kidney stones form?
Kidney stones form when minerals that are normally dissolved in the urine precipitate out of their dissolved state to form solid crystals. This crystal formation often occurs after meals or during periods of dehydration. Most kidney stones manifest themselves during sleep, at a time of maximal dehydration.
Dehydration is also why kidney stones occur much more commonly during hot summer days than during the winter. Anything that promotes dehydration can help bring upon a stone, including exercise, saunas, hot yoga, diarrhea, vomiting, being on bowel prep for colonoscopy, etc.
In addition to dehydration, another factor that can contribute to kidney stone formation is excessive intake of certain vitamins. The biggest culprit is Vitamin C, also known as ascorbic acid. When metabolized by the body, vitamin C is converted into oxalate, one of the components of calcium oxalate stones, the most common type of stone. The problem is that vitamin C is a water-soluble vitamin, so any excessive intake is not stored in the body but appears in the urine in the form of oxalate.
Additionally, excessive dietary protein intake, fat intake, and sodium are all associated with an increased risk for kidney stones. Having inflammatory bowel disease or previous intestinal surgery can also increase the risk for stones. Urinary infections with certain bacteria can promote stone formation. Having a parathyroid issue and high circulating calcium levels is another cause of kidney stones. Obesity is also a risk factor for kidney stones. Some stones have a genetic basis, with a tendency to affect many family members.
A kidney stone starts out as a tiny sand particle that grows as the “grain” is bathed in urine that contains minerals. These minerals are deposited and coalesce around the grain. They can grow to a very variable extent so that when they start causing symptoms they may range from being only a few millimeters in diameter to filling the entire kidney.
What are the symptoms?
Some stones are “silent” because they cause no symptoms and are discovered when imaging studies are done for other reasons. However, most stones cause severe pain known as colic. Colicky pain is often intermittent, originating in the flank area and radiating down towards the groin. It often causes an inability to get comfortable in any position, and is associated with sweating, nausea, and vomiting. Kidney stones can also cause blood in the urine, sometimes visible and, at other times, only on a microscopic basis.
When a stone moves into the ureter (the tube running from the kidney to the bladder), it can become impacted and block the flow of urine. Stones can sometimes cause lower urinary tract symptoms such as urgency and frequency, particularly when the stone approaches the very terminal part of the ureter that is actually tunneled through the wall of the bladder.
How are they diagnosed?
Kidney stones are usually easily diagnosed, based upon their rather classical presentation. However, on occasion, a stone causes no symptoms whatsoever and is picked up incidentally on an imaging study such as an ultrasound, a CAT scan, or an MRI. The imaging study of choice for evaluating a kidney stone is an unenhanced CAT scan (without contrast). A plain x-ray of the abdomen is very useful for stones that contain calcium, and thus are readily visible on an x-ray.
How are they treated?
Most stones will pass spontaneously without intervention given enough time. Conservative management involves hydration, analgesics and the use of a class of medications known as alpha-blockers that can help facilitate stone passage by relaxing the ureteral smooth muscle. As long as the pain is manageable and there is progressive movement of the stone seen on imaging studies, conservative management can continue to be an option.
Intervention is mandated under the following circumstances: intolerable pain; refractory nausea and vomiting with dehydration; larger stones that are not likely to pass; failure of a stone to pass after a reasonable amount of time; significant obstruction of the kidney; a high fever from a kidney infection that does not respond to antibiotics; a solitary kidney; and certain occupations that cannot risk impaired functions such as an airline pilot.
There are a number of minimally invasive means of treating kidney stones depending upon the size of the stone, its location, and the degree of obstruction of the urinary tract. Gone are the days when treating a kidney stone required a painful incision and a prolonged stay in the hospital. Shockwave lithotripsy is commonly used to treat stones in the kidney or upper ureter. Typically done under intravenous sedation, shockwave lithotripsy uses shock waves directed at the kidney stone via x-ray guidance to fragment the stones into pieces that are small enough so that they then can then pass down the ureter, into the bladder and out the urethra with the act of urinating.
Another means of managing stones, particularly amenable to stones in the lower ureter but also applicable to any stone, is ureteroscopy and laser lithotripsy. This procedure is done under general anesthesia. A narrow lighted instrument known as a ureteroscope is passed up the ureter to visualize the stone under direct vision. A laser fiber is then utilized to break the stone into tiny particles. The largest fragments are removed using a special basket. A ureteral stent is often left in place after this procedure to allow the ureter to heal as well as to prevent obstruction of the kidney.
What are the risk factors?
You are at high risk for kidney stones if you:
- Don’t drink enough fluids
- Have an occupation that requires working in hot environments
- Exercise strenuously without maintaining adequate hydration
- Are a male, since the male to female ratio of kidney stone incidence is 3:1
- Had a previous kidney stone, since about 50% of people who have a stone will experience a recurrence
- Have a family history of kidney stones
- Have a urinary tract obstruction
- Have an excessive intake of oxalate, calcium, salt, protein and fat
- Take excessive amounts of vitamin C, A, and D
- Have an intestinal malabsorption
- Have gout
- Have parathyroid disease
Kidney Stone Prevention
The key to preventing kidney stones is to stay well hydrated, particularly when exposed to hot environments or when exercising for prolonged periods of time. It is also important to avoid overdoing it with certain vitamins—particularly vitamin C. The two biggest risk factors for kidney stones are, in fact, dehydration and excessive intake of vitamin C. Chances are that if you have a healthy diet, you have more than adequate intake of vitamin C and any extra is potentially dangerous. A good sign of adequate hydration is the color of your urine: the urine of a well-hydrated person will look light in color like lemonade, whereas the urine of a dehydrated person will look like apple juice.
So drink up, particularly on hot days…and squeeze some citrus fruit into your water instead of popping a vitamin C supplement…your kidneys will thank you!
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