Kidney stones are solid accretions (crystals) of dissolved minerals in urine found inside the kidneys or ureters. Also known as nephrolithiasis, urolithiasis or renal calculi. They vary in size from as small as a grain of sand to as large as a golf ball. Kidney stones typically leave the body in the urine stream; if they grow relatively large before passing (on the order of millimeters), obstruction of a ureter and distention with urine can cause severe pain most commonly felt in the flank, lower abdomen and groin.

Conventional wisdom has held that consumption of too much calcium can aggravate the development of kidney stones, since the most common type of stone is calcium oxalate. However, strong evidence has accumulated demonstrating that low-calcium diets are associated with higher stone risk and vice-versa for the typical stone former. The relatively dense calcium renders these stones radio-opaque and they can be detected by a traditional X-ray of the abdomen that includes Kidneys, Ureters and Bladder-KUB. Computed tomography, a specialized X-ray, is by far the most accurate diagnostic test for the detection of kidney stones. Other examples of kidney stones include struvite (magnesium, ammonium and phosphate), uric acid, calcium phosphate, or cystine (the amino acid found only in people suffering from cystinuria). The formation of struvite stones is associated with the presence of certain bacteria which can split urea into ammonia, most commonly Proteus mirabilis. There are many types of kidney stone, and a person may be susceptible to only some of them.

Symptoms

Purply-green stones are usually idiopathic and asymptomatic until they obstruct the flow of urine. Symptoms can include acute flank pain ("renal colic"), nausea and vomiting, restlessness, dull pain, hematuria, and possibly fever if infection is present. Acute renal colic is described as one of the worst types of pain that a patient can suffer from.

Treatment

Stones less than 5 mm in size usually will pass spontaneously; the majority of stones greater than 6 mm will require some form of intervention.

Surgery is rarely used to remove kidney stones; instead pain management with diclofenac is used while waiting for the stone to pass on its own. However, in certain cases, Extracorporeal Shock Wave Lithotripsy (ESWL - see lithotriptor), retrograde ureteral or intrarenal surgery , percutaneous nephrolithotripsy , or open surgery may be necessary. This is especially so if the stone is stuck, causing obstruction and infection of the urinary tract. Laser, ultrasonic, and mechanical (pneumatic, shock-wave) are forms of energy employed to fragment stones. However, laser treatment on certain types of stones may lead to release of poisonous arsenic from the stone.

Preventive strategies include dietary modifications such as drinking enough water to make 2-2.5 litres of urine per day. Restriction of animal protein and sodium intake are beneficial as well as certain medications, eg, potassium citrate and allopurinol depending on the cause of stone formation. Restriction of oxalate-rich foods and maintaining an adequate intake of dietary calcium is recommended. There is no convincing evidence that calcium supplements increase the risk of stone formation.

Recent research

Controversial recent research has suggested a link between kidney stones and the presence of a putative lifeform that has been called nanobacteria. If this should be proven to be true then there would be important implications for their treatment and prevention

More information

Kidney stones are unrelated to gallstones.

The author Isaac Asimov suffered from kidney stones, and wrote about how his pain was treated with morphine, saying that he feared becoming addicted to it if he ever needed it again.

See also

• Nephrology
• Urinary retention
• Urology

External links

• http://www.herringlab.com/photos/ - Pictures of kidney stones, showing their crystalline shape