Facts on Kidney Stones
- The kidney acts as a filter for blood, removing waste products from the body and making urine. It also helps regulate electrolyte levels that are important for body function. Urine drains from the kidney through a narrow tube called the ureter into the bladder. When the bladder fills and there is an urge to urinate, the bladder empties to the outside through the urethra, a much wider tube than the ureter.
- In some people, chemicals crystallize in the urine and may form a kidney stone. These stones are very tiny when they form, smaller than a grain of sand, but gradually can grow over time to an inch or larger.
- Urolithiasis is the term that refers to the presence of stones in the urinary tract, while nephrolithiasis (nephro = kidney + lithiasis = stone) refers to kidney stones and ureterolithiasis refers to stones lodged in the ureter.
- The size of the stone is important, but where it is located and whether it obstructs or prevents urine from draining can be just as important.
- When the stone sits in the kidney, it rarely causes pain, but when it falls into the ureter, it acts like a dam. As the kidney continues to function and make urine, pressure builds up behind the stone and causes the kidney to swell.
- This pressure is what causes the pain of a kidney stone, but it also helps push the stone along the course of the ureter. When the stone enters the bladder, the obstruction in the ureter is relieved and the symptoms of a kidney stone are resolved.
What Causes Kidney Stones?
There is no consensus as to why kidney stones form.
- Heredity: Some people are more susceptible to forming kidney stones, and heredity may play a role. The majority of kidney stones are made of calcium, and hypercalciuria (high levels of calcium in the urine) is one risk factor. The predisposition to high levels of calcium in the urine may be passed on from generation to generation. Some rare hereditary diseases also predispose some people to form kidney stones. Examples include people with renal tubular acidosis and people with problems metabolizing a variety of chemicals including cystine (an amino acid), oxalate, (a salt of an organic acid), and uric acid (as in gout).
- Geographical location: There may be a geographic predisposition to forming kidney stones, so where a person lives may make it more likely for them to form kidney stones. There are regional "stone belts," with people living in the southern United States having an increased risk of stone formation. The hot climate in this region combined with inadequate fluid intake may cause people to be relatively dehydrated, with their urine becoming more concentrated and allowing chemicals to come in closer contact to form the nidus, or beginning, of a stone.
- Diet: Diet may or may not be an issue. If a person is susceptible to forming stones, then foods high in animal proteins and salt may increase the risk; however, if a person isn't susceptible to forming stones, diet probably will not change that risk.
- Medications: People taking diuretics (or "water pills") and those who consume excess calcium-containing antacids can increase the amount of calcium in their urine and potentially increase their risk of forming stones. Taking excess amounts of vitamins A and D are also associated with higher levels of calcium in the urine. Patients with HIV who take the medication indinavir (Crixivan) may form indinavir stones. Other commonly prescribed medications associated with stone formation include phenytoin (Dilantin) and antibiotics like ceftriaxone (Rocephin) and ciprofloxacin (Cipro).
- Underlying illnesses: Some chronic illnesses are associated with kidney stone formation, including cystic fibrosis, renal tubular acidosis, and inflammatory bowel disease.
Picture of a kidney stone
Medically Reviewed by a Doctor on 10/19/2016
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