Kidney Stones Overview The kidney acts as a filter for blood, making urine and removing waste products from the body. It also helps regulate electrolyte levels that are important for body function. Urine drains from the kidney into the bladder through a narrow tube called the ureter. When the bladder fills and there is an urge to urinate, the bladder empties through the urethra, a much wider tube than the ureter. In some people, chemicals crystallize in the urine and form the beginning, or nidus, of a kidney stone. These stones are very tiny when they form, smaller than a grain of sand, but gradually can grow over time to a 1/10 of an inch or larger. Urolithiasis is the term that refers to the presence of stones in the urinary tract, while nephrolithiasis refers to kidney stones. The size of the stone doesn’t matter as much as where it is located. Kidney Stones Causes 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 a 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 type of salt), and uric acid (as in gout). Geographical location: There may be a geographic predisposition 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 and poor 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 calcium may increase the risk; however, if a person isn’t susceptible to forming stones, diet 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) can form indinavir stones. Other commonly prescribed medications associated with stone formation include 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. Kidney Stones Symptoms and Signs Renal colic (renal is the medical term for things related to the kidney) has a classic presentation when a kidney stone is being passed.

• The pain is intense and comes on suddenly. It may wax and wane, but there is usually a significant underlying ache between the acute spasms of pain.
• It is usually located in the flank or the side of the mid-back and radiates to the groin.
• Those affected cannot find a comfortable position, and many writhe in pain.
• Sweating, nausea, and vomiting are common.
• Blood may be visible in the urine because the stone has irritated the ureter. Blood in the urine (hematuria), however, does not always mean a person has a kidney stone. There may be other reasons for the blood, including kidney and bladder infections, trauma, or tumors. Urinalysis with a microscope may detect blood even if it is not appreciated by the naked eye. Sometimes, if the stone causes complete obstruction, no blood may be found in the urine because it cannot get past the stone.

Outlook Once a patient has passed a stone, there is a great likelihood that another stone will be passed in his or her lifetime. Since kidney stones may also be hereditary, this likelihood is passed on to the next generation. A patient who has experienced a stone is unlikely to forget the experience and often will arrive at the health-care facility already knowing the diagnosis. Those with recurrent stones may be given medication to keep at home should symptoms recur.