Kidney Stones (cont.)
Melissa Conrad Stöppler, MD
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
William C. Shiel Jr., MD, FACP, FACR
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
In this Article
- Kidney stone facts
- What is a kidney stone?
- Who is at risk for kidney stones?
- What causes kidney stones?
- What are the signs and symptoms of kidney stones?
- How are kidney stones diagnosed?
- What is the treatment for kidney stones? How long does it take to pass a kidney stone?
- Can kidney stones be prevented?
- What is the prognosis for kidney stones?
- Pictures of Kidney Stones - Slideshow
- Pictures of Kidney Stones - Image Collection
- The 7 Wonders of Water - Slideshow
- Find a local Urologist in your town
Who is at risk for kidney stones?
Anyone may develop a kidney stone, but people with certain diseases and conditions (see below) or those who are taking certain medications are more susceptible to their development. Urinary tract stones are more common in men than in women. Most urinary stones develop in people 20-49 years of age, and those who are prone to multiple attacks of kidney stones usually develop their first stones during the second or third decade of life. People who have already had more than one kidney stone are prone to developing further stones.
In residents of industrialized countries, kidney stones are more common than stones in the bladder. The opposite is true for residents of developing areas of the world, where bladder stones are the most common. This difference is believed to be related to dietary factors. People who live in the southern or southwestern regions of the U.S. have a higher rate of kidney stone formation than those living in other areas. Over the last few decades, the percentage of people with kidney stones in the U.S. has been increasing, most likely related to the obesity epidemic.
A family history of kidney stones is also a risk factor for developing kidney stones. Kidney stones are more common in Asians and Caucasians than in Native Americans, Africans, or African Americans.
Uric acid kidney stones are more common in people with chronically elevated uric acid levels in their blood (hyperuricemia).
A small number of pregnant women develop kidney stones, and there is some evidence that pregnancy-related changes may increase the risk of stone formation. Factors that may contribute to stone formation during pregnancy include a slowing of the passage of urine due to increased progesterone levels and diminished fluid intake due to a decreasing bladder capacity from the enlarging uterus. Healthy pregnant women also have a mild increase in their urinary calcium excretion. However, it remains unclear whether the changes of pregnancy are directly responsible for kidney stone formation or if these women have another underlying factor that predisposes them to kidney stone formation.
What causes kidney stones?
Kidney stones form when there is a decrease in urine volume and/or an excess of stone-forming substances in the urine. The most common type of kidney stone contains calcium in combination with either oxalate or phosphate. A majority of kidney stones are calcium stones. Other chemical compounds that can form stones in the urinary tract include uric acid, magnesium ammonium phosphate (which forms struvite stones; see below), and the amino acid cysteine.
Dehydration from reduced fluid intake or strenuous exercise without adequate fluid replacement increases the risk of kidney stones. Obstruction to the flow of urine can also lead to stone formation. In this regard, climate may be a risk factor for kidney stone development, since residents of hot and dry areas are more likely to become dehydrated and susceptible to stone formation.
Kidney stones can also result from infection in the urinary tract; these are known as struvite or infection stones. Metabolic abnormalities, including inherited disorders of metabolism, can alter the composition of the urine and increase an individual's risk of stone formation.
A number of different medical conditions can lead to an increased risk for developing kidney stones:
- Gout results in chronically increased amount of uric acid in the blood and urine and can lead to the formation of uric acid stones.
- Hypercalciuria (high calcium in the urine), another inherited condition, causes stones in more than half of cases. In this condition, too much calcium is absorbed from food and excreted into the urine, where it may form calcium phosphate or calcium oxalate stones.
- Other conditions associated with an increased risk of kidney stones include hyperparathyroidism, kidney diseases such as renal tubular acidosis, and other inherited metabolic conditions, including cystinuria and hyperoxaluria.
- Chronic diseases such as diabetes and high blood pressure (hypertension) are also associated with an increased risk of developing kidney stones.
- People with inflammatory bowel disease are also more likely to develop kidney stones.
- Those who have undergone intestinal bypass or ostomy surgery are also at increased risk for kidney stones.
- Some medications also raise the risk of kidney stones. These medications include some diuretics, calcium-containing antacids, and the protease inhibitor indinavir (Crixivan), a drug used to treat HIV infection.
- Dietary factors and practices may increase the risk of stone formation in susceptible individuals. In particular, inadequate fluid intake predisposes to dehydration, which is a major risk factor for stone formation. Other dietary practices that may increase an individual's risk of forming kidney stones include a high intake of animal protein, a high-salt diet, excessive sugar consumption, excessive vitamin D supplementation, and excessive intake of oxalate-containing foods such as spinach. Interestingly, low levels of dietary calcium intake may alter the calcium-oxalate balance and result in the increased excretion of oxalate and a propensity to form oxalate stones.
- Hyperoxaluria as an inherited condition is uncommon and is known as primary hyperoxaluria. The elevated levels of oxalate in the urine increase the risk of stone formation. Primary hyperoxaluria is much less common than hyperoxaluria due to dietary factors as mentioned above.
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