Kidney Stones
To Your Health -- CHRC Newsletter
Summer 2008
Summer in the Bay Area is a time for outdoor relaxation, summer camps, family get-togethers, and barbeques – unless you are passing a kidney stone. Stones are just that, little hard pebbles not unlike the ones you pick up off the pavement. They are formed from over-saturation of urine with salts and proteins. Formed in the kidney, stones will cause symptoms when they have grown to be large or if they drop into the ureter, the tube that drains urine from the kidney. As temperatures climb during the summer and we become more dehydrated with outdoor activities, our risk for developing kidney stones goes up. Women passing stones tell me that kidney pain (or "colic") feels like labor, and men, well, some are in so much pain that they are curled up in a ball and can't talk at all. In this article, we will look at the different types of stones and ways to lower your risk. We’ll also help you recognize the acute symptoms of renal colic, followed by a review of treatment and prevention.
Risk Factors
Kidney stones are common, with 10 percent of men and 5 percent of women affected at some point in their lives. Risk factors include dehydration, male gender, obesity, sedentary lifestyle/occupation, hyperparathyroidism, certain diuretics, chronic use of antibiotics, and inflammatory bowel conditions. When we consider medical conditions of the urinary tract, only prostate conditions in men and urinary tract infections are more common than stones.
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Types of Kidney Stones
In the United States, 85 percent of stones are calcium oxalate with 10 percent made up of uric acid, 1 percent of cystine, and the rest considered "infectious" stones.
Calcium and oxalates come from your diet. Separately, they are soluble, but when they come together in the urine, they "stick" together into crystals and form a kidney stone. Foods high in oxalates include rhubarb, strawberries, spinach, nuts, chocolate, and others. Lowering dietary intake of these foods can help. While counter-intuitive, drinking a glass of milk or taking dietary calcium at the same time of dietary oxalate intake will help decrease free oxalate absorption by the intestines. In effect, calcium oxalate crystals form in the gut, and the body will remove them in the stool. High oxalate intake without calcium, however, will lead to high oxalate absorption from the intestines. Absorbed oxalates reach the blood stream and will have to be removed and processed by the kidney. It is in the kidney that oxalates can bind to calcium and form calcium oxalate crystals/stones.
Besides dietary intake, patients with chronic diarrhea or inflammatory bowel disorder are at high risk for this type of stone because there is often not enough calcium in the gut to bind the oxalates. Treatment may sometimes require dietary calcium supplements, such as TUMS®, with meals and aggressive management of the inflammatory bowel disorder. Within the large intestine there are also "good" bacteria that help breakdown oxalates. Chronic uses of high-dose antibiotics can eliminate the "good" bacteria and cause elevated oxalate absorption. Discontinuing or lowering antibiotic dosing can restore the balance.
A second type of kidney stone is made up of uric acid, an organic by-product from dietary animal proteins and from internal protein turnover. Uric acids are soluble in urine up to a certain level, and this solubility is highly dependent on the overall pH or acidity of the urine. Unlike calcium oxalate, uric acid stones can dissolve when the urine acidity is lowered with medical "alkalinization" therapy (i.e., by increasing urinary pH). Depending on the level of acidity, treatment can be as simple as adding a spoon of baking soda to a glass of water taken several times a day. In addition, there are prescription medications that can lower uric acid levels. Sometimes used for patients with gout, allopurinol can lower uric acid levels and minimize uric acid crystal build-up in joints and in the urinary tract. Interestingly, only 10 percent of patients with gout and high uric acid levels have kidney stones. This is of course due to the complex nature of stone formation as there are other compounds in the body that can lower stone risk. One such compound is citrate, found in lemons and oranges. In fact, "lemonade therapy" is a safe and natural way to lower your risk for kidney stones.
Cystine stone is rare and is associated with a hereditary medical condition. Patients with cystinuria lack an enzyme in their body such that they are unable to process certain amino acids. Cystine, an amino acid and a by-product of protein metabolism, is present in very high levels. Patients will often present early in life and will have many stones in their life-time. Treatment requires prescription medication such as Thiola® and high fluid intake.
Infections of the urinary tract can cause struvite or infectious stones. Urinary bacteria such as Proteus species can promote crystallization of salts by lowering urine acidity (i.e., by increasing urinary pH). These stones typically will not dissolve. Further, once formed, the stone matrix provides protection for bacteria where antibiotics may not be effective. Surgical stone removal is often necessary.
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Symptoms
Although the composition of kidney stones can vary, the clinical symptoms of acute renal colic are similar. Pain occurs because the offending stone is irritating the kidney or has plugged up the ureter. Pain comes in waves and is localized high in the flank or back just underneath the ribs. Physiologically, colic is caused by spasm of the ureter and back pressure on the blocked kidney. As the stone moves down the ureter, the pain can move to the front of the lower abdomen or groin area on the same side. Similar to labor in women, the pain is internal, and this can sometimes be difficult to localize to a specific area on the body. Unlike muscle spasm or muscle strain of the back, changing body positions does not help. In addition, patients can experience severe nausea and sometimes vomiting. Some individuals report burning on urination, frequency, urgency, and even blood in the urine.
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Diagnosis and Treatment
The first step in treatment is pain control and hydration. The level of pain will dictate the type of pain medication required. When pain or nausea is severe, oral and intramuscular pain medications may not be adequate. An intravenous line may be placed for pain medications and for hydration. Blood and urine samples are checked to make sure that kidney function is not severely impaired and that there is no infection. X-rays are taken to identify and characterize stone size, numbers, and location.
A solitary stone that is less that 5mm will usually pass on its own within the next two to four weeks regardless of location in the ureter. For larger stones, the success of spontaneous passage goes down as the size goes up. Stones between 6-8 mm have a 15-40 percent of passing, and stones greater than 9-10mm will usually not pass on their own. In choosing "medical expulsion" therapy – to allow the stone to pass on its own, your pain must be controlled by pain pills, you must be able to keep down fluids, and have no evidence infection on your tests. The amount of fluid intake should be about eight to ten, 8-ounce cups a day. "Pushing fluids" beyond this amount probably will not have additional benefit. Over the last five years, we have found that “alpha-blocker” medications (such as Flomax®) can increase the success of medical expulsion therapy with shorter times to spontaneous passage. Your treating doctor will determine if you can take this medication.
"Endoscopic" management is needed if pain can not be controlled or if there is evidence of complications such as kidney failure or infection. The initial treatment goal is drainage. Without making a cut in your body, the urologist places an internal stent that traverses the entire ureter, by-passes the stone, and allows direct urine drainage from the kidney to the bladder. Stents are soft tubes about the size of a spaghetti noodle with an internal channel and numerous side-holes. With drainage re-established, the blocked kidney is given one to two weeks to recover, and infection (if present) is treated.
After one to two weeks of recovery, the urologist will remove the stone. This can be done with miniature telescopes called ureteroscopes. They are similar in size to the stents and are flexible with a working channel where stone-baskets and lasers can be used to capture stone fragments. The removed stone will be sent for chemical or stone analysis. For kidney stones high in the kidney, shock-wave therapy can also be used.
The ability of shock waves to break brittle and hard objects was noted when jet aircrafts flew over buildings at low altitudes. Windows broke and metal pipes cracked. The shock waves are generated by compression of air by the fast moving jet. The waves travel through air and break brittle objects. In breaking kidney stones, shock-waves are generated by a machine that the patient lies on. The treating doctor pushes a button on the machine, and shock waves are transmitted through the body and focused onto the stone. The energy of the shock waves break the stone into dust; over the ensuing month, the dust will pass in the urine. At home, you will be instructed to capture the fragments with a stone-strainer (like mining for gold).
In general, soft body tissues are not harmed by shock waves; tissues simply compress and stretch to the shock waves. To understand why this is, imagine shock waves as baseballs that are thrown out by the machine. When the baseballs (or shock waves) hit a hard and brittle target, the target breaks. However, when the baseballs hit a soft target like a pillow, the target compresses and stretches.
On occasion, the stone volume is too high to be treated successfully with ureteroscopy or shock-waves. This is sometimes seen in patients with "staghorn" stones that fill the entire kidney. On X-rays these stones will literally look like a deer’s horns. To remove these complex stones, the urologist may need to make a 1 cm incision in your back. Through this tiny incision, the stone is broken up with ultrasound energy, and the stone fragments evacuated. This approach is called "percutaneous."
In 2008, open surgery for kidney stones has been replaced by minimally-invasive endoscopic approaches. Patient recovery is fast and stone treatment is an outpatient procedure for most. However, it is still best to prevent stones. In general, there are three things you can do to minimize your stone risk. The first is to ensure adequate fluid intake in the summer. You need to drink enough to produce between seven to nine, 8-ounce cups of urine a day. Second, cutting back on "sodium" and salty foods will help decrease your risk for salt crystallization and stone formation in the urine. Third, spreading out your intake of meat products will decrease organic acid loads to your kidneys. This is important because organic acids like uric acid from meat products can contribute to stone growth. Remember, this includes not only red meat but also white meat like chicken and fish.
For those who have passed a stone, the risk of stone recurrence is about 10 percent in the next year, and up to 50 percent in five years. To help lower this risk, a complete metabolic work-up with blood tests and 24-hour urine collection is helpful. Based on the results of the work-up, medications and supplements can be effective. Your urologist can work closely with you and establish your treatment plan.
Enjoy your summer and remember your ice-cold lemonade. Cheers.
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