A kidney stone is a hard, crystalline mineral material formed within the kidney or urinary tract. Kidney stones are a common cause of blood in the urine (haematuria) and often severe pain in the abdomen, flank, or groin. Kidney stones are sometimes called renal calculi.
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. About 75% of kidney stones are calcium stones. Other chemical compounds that can form stones in the urinary tract include uric acid, magnesium ammonium phosphate and the amino acid cystine.
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.
While some kidney stones may not produce symptoms (known as "silent" stones), people who have kidney stones often report the sudden onset of excruciating, cramping pain in their low back and/or side, groin, or abdomen. Changes in body position do not relieve this pain. The abdominal, groin, and/or back pain typically waxes and wanes in severity, characteristic of colicky pain (the pain is sometimes referred to as renal colic). It may be so severe that it is often accompanied by nausea and vomiting. The pain has been described by many as the worst pain of their lives, even worse than the pain of childbirth or broken bones. Kidney stones also characteristically cause blood in the urine. If infection is present in the urinary tract along with the stones, there may be fever and chills. Sometimes, symptoms such as difficulty urinating, urinary urgency, penile pain, or testicular pain may occur due to kidney stones.