Kidney stones (also known as renal lithiasis) are hardened material found inside the kidneys, and are made of crystallized minerals and salts. They can occur anywhere along the urinary tract, between the kidney and bladder, and vary in shape and size - some are as large as a golf ball. The main cause of kidney stones is a lack of fluids, which allows salts and minerals to concentrate and crystallize over the course of weeks to months. Passing a stone can be painful and may even require surgery. Approximately 1 in 11 Americans have kidney stones, with data showing an increasing trend in the prevalence of this disease.
Causes and Risk Factors
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The lack of proper hydration signified by producing less than 1 liter of urine daily is the primary cause of kidney stone disease. Urine is largely made up of water, which acts as the solvent for calcium, oxalate, uric acid, and other crystal-forming substances found in urine. Without ample water, urine becomes supersaturated allowing these components to fall out of solution and crystallize. The cause usually depends on the type of kidney stone, as summarized below:
Calcium stones. The most common of kidney stones are made of calcium, usually in the form of calcium oxalate, and sometimes, calcium phosphate. Calcium is derived from diet and is required for muscle function and bone mass. Excess calcium is excreted in the urine, where it can combine with oxalate. Certain fruits and vegetables, vitamin supplements, and metabolic disorders can lead to increased levels of oxalate.
Struvite stones. Struvite (phosphate mineral) stones are associated with bacterial infections of the urinary tract. Ammonia-producing bacteria are believed to enable crystallization by increasing the pH of urine. Struvite stones can become large enough to block in the urinary tract.
Uric acid stones. Uric acid stones are more common in men and are linked to a high-protein diet. They may also occur in individuals with gout.
Cystine stones. These stones develop in individuals with a hereditary condition called cystinuria, in which an excess of the amino acid cystine leaks into the urine.
Other risk factors for kidney stone disease include a family history of the disease, diet, and certain medical conditions.
Disease history. Individuals with past kidney stones or with a family history of kidney stones are at a greater risk.
Diet. Foods that are high in animal protein, sodium, and sugar are linked to a greater risk of developing kidney stones.
Medical conditions. Digestive diseases like inflammatory bowel disease (IBD) and chronic diarrhea, and conditions like hyperparathyroidism can increase the risk of kidney stones.
Age and gender. Kidney stones are common in adults over the age of 40, and more prevalent in men.
Small kidney stones are generally asymptomatic and may be cleared through urine with little to no pain. Large kidney stones that block the path of urine can cause more severe symptoms, such as:
Sharp pain in the abdomen or lower back
Blood in the urine
Nausea and vomiting
Fever and chills
Abnormally colored urine.
Diagnosis and Treatment
The first step in diagnosing kidney stones is a physical exam and an assessment of known risk factors. Next, the following tests may be performed to detect the stones and identify the cause:
Blood test. Blood tests look for elevated levels of crystal-forming substances (uric acid and calcium) in the blood, and also evaluate kidney function.
Urinalysis. This test measures the levels of crystal-forming and crystal-inhibiting components in urine, and detects actual kidney stone. Urinalysis also tests for a urinary tract infection, which can lead to struvite stones.
Treatment options for kidney stones depend on the type of stone and level of discomfort. Small stones can be passed from the body by drinking plenty of water (over 2 liters daily) and using pain medication (over-the-counter or prescription), as needed. The following are common treatments for patients with large stones or severe symptoms:
Medication. Some kidney stones can be broken apart or dissolved using diuretics, phosphate solution, or sodium bicarbonate. Allopurinol is used to treat uric acid stones, while antibiotics help treat the cause of struvite stones. Medications that relax the ureter muscles may be prescribed to help pass kidney stones.
Shock wave lithotripsy. This procedure helps break up larger stones by using strong sound vibrations. Once crushed, the small crystal fragments can be passed through urine.
Percutaneous nephrolithotomy. During this surgical procedure, a thin tool is passed through the patient’s back and into the kidney, where it can remove kidney stones.
Uteroscopy. A uteroscope is a thin, lighted tube equipped with a camera to visualize kidney stones. The device is inserted into the urinary tract through the urethra, where it can remove small stones, or break them apart using energy from a laser.
Proper hydration is the best preventative measure for kidney stone disease. Individuals who have had kidney stones can help prevent a recurrence by altering their diet. For example, limiting animal proteins helps prevent uric acid and calcium stones, while reducing high-oxalate foods (e.g. spinach) and sodium helps prevent calcium oxalate and calcium phosphate stones, respectively. Depending on the type of stone, modifications to existing medications may also help prevent recurrence.
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“What I need to know about Kidney Stones”. National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC). NIH. Jul 2013. Retrieved May 23, 2014. http://kidney.niddk.nih.gov/kudiseases/pubs/stones_ez/.
Scales, C.D. Jr., Smith, A.C., Hanley, J.M., Saigal, C.S., Urologic Diseases in America Project. Prevalence of kidney stones in the United States. Eur Urol. 2012. 62(1):160-5.