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Frequently Asked Questions

Kidney stones are small, hard deposits made of mineral and acid salts that form inside the kidney.  Stones often form when the minerals stick together when the urine becomes concentrated.

There are 4 basic types of kidney stones. Each has a different cause, and therefore each may require slightly different preventative steps. The type of a stone is determined from chemical analysis of stone fragments passed in the urine following lithotripsy. Once the type has been determined, your physician can recommend dietary and lifestyle changes that should help prevent their recurrence.

Calcium stones

Ninety percent of stones contain calcium combined with another mineral. The most common type of calcium stone is calcium oxalate. Calcium may also combine with phosphate, forming insoluble crystals. Crystal formation is dependent on three things: temperature, pH, and concentration. We can't do much to change the temperature inside our bodies, so the only two things we can control are pH and concentration. Normally, urine contains substances that inhibit crystal formation, so some people will form stones, and others with the same concentration and pH will not. One way to control concentration is by diluting with water. Drinking 8 to 10 glasses of water per day or more will lower the mineral concentration enough to reduce or eliminate further stone formation. By reducing the intake of oxalate (sources include dark green vegetables, soy products, nuts, and chocolate) and phosphate (table salt, beef, pork, and poultry), and increasing dietary fiber, some people can reduce their risk of forming more stones. There are many medical diseases, such as hyperparathyroidism, several kidney diseases, and intestinal bypass surgery that may result in high concentrations of minerals in the urine. People with these diseases eat normal amounts of calcium but absorb too much of it from their intestines. In other people the kidney leaks large amounts of calcium into the urine, even on a calcium restricted diet. As you can see, this is a complicated topic, so please consult your doctor for more information.

Uric acid stones

One end product of protein metabolism is uric acid. Uric acid can form crystals with or without combining with other minerals. These stones are unique, however, in that they tend to form in acidic urine (pH of 5 or 6) and are soluble in alkaline urine (pH of 7 or 8). A high protein diet may contribute to this type of stone. These stones can frequently be prevented by a combination of: high fluid intake, e.g., four quarts of water per day; allopurinol, a drug that lowers uric acid concentration; and medication such as Shohl's solution to alkalinize the urine (raise the pH).

Cystine stones

These account for 1 percent of all stones. They are usually found in young individuals who possess a genetic defect which affects their ability to metabolize protein. As a result, they secrete large amounts of the amino acid cystine in the urine. Patients with this disease need ongoing, highly individualized treatment for the duration of their lives.

Ammonium magnesium phosphate stones (struvite)
These stones are uncommon and usually are associated with chronic urinary infection. Treatment consists of removal of all of the stone present followed by treatment of the infection with antibiotics.

Although referred to generically as "kidney stones," stones can form in the kidneys, in the ureters (tubes which connect the kidneys to the bladder), and in the bladder. These are shown visually in the illustration below.

Areas of Kidney Stone Formation

Some kidney stones are painless and only discovered as an incidental finding on x-ray. Many renal stones are discovered when a patient is evaluated for blood in the urine. Most ureteral stones are diagnosed when patients come to the emergency room with sudden onset of severe pain in the back or abdomen. The pain is not always severe, but it can be severe enough to be incapacitating. It may be associated with nausea and vomiting. If fever and chills accompany the pain, immediate medical attention is mandatory, as this may indicate an infection is present in the urinary tract.

There is no one "best treatment," but there are some general guidelines. If the size of the stone is less than 5 millimeters, (1/5 inch) and it is located in the ureter, it will usually pass spontaneously. If the size of the stone is between 5 millimeters and 10 millimeters (1/5-2/5 inch), and it is located in the ureter, it will often pass into the lower third of the ureter where it can be removed by ureteroscopy and either a stone basket or a laser. Stones in the kidney are usually treated with ESWL if they are less than 20 millimeters (4/5 inch) in length and 20 millimeters in width. If they are larger than 20 millimeters, they often require a combined approach using both percutaneous nephrostomy and ESWL.

ESWL stands for Extracorporeal Shock Wave Lithotripsy. ESWL is a non-invasive treatment for kidney stones using an acoustic pulse to fragment the stones into smaller pieces that can then pass out of the body through the urinary tract.

We recommend resuming sexual activity when

  1. You are feeling well enough not to need pain medication.
  2. You are eating and taking liquids normally.
  3. There is no blood visible in your urine.

We recommend returning to work when

  1. You are feeling well enough not to need pain medication.
  2. You are eating and taking liquids normally.
  3. There is no blood visible in your urine.

Most patients return to work after one or two days following lithotripsy.

A stent is a small plastic tube that can be placed inside the natural passage of the urinary tract. One end curls in the kidney, and the other end curls in the urinary bladder. A stent may be placed before lithotripsy in order to relieve obstruction or to help locate a stone during ESWL. Patients with stents usually notice that they must urinate more frequently, have a sense of urgency to urinate, and may have back pain during urination. These symptoms usually subside gradually over two or three days. If a stent is needed, the doctor will explain the reason it is needed and will establish a plan for removing the stent.

Stents need to be removed in a timely manner because they can become coated with compounds similar to stones and therefore can be difficult to remove without additional open surgery.