A kidney stone, also known as a renal calculus or nephrolith, is a solid piece of material which is formed in the kidneys from minerals in urine. Kidney stones typically leave the body in the urine stream, and a small stone may pass without causing symptoms. If stones grow to sufficient size (usually at least 3 millimeters (0.1 in)) they can cause blockage of the ureter.
This leads to pain, most commonly beginning in the flank or lower back and often radiating to the groin. This pain is often known as renal calculus and typically comes in waves lasting 20 to 60 minutes. Other associated symptoms include: nausea, vomiting, fever, blood in the urine, pus in the urine, and painful urination. Blockage of the ureter can cause decreased kidney function and dilation of the kidney.
Most stones form due to a combination of genetics and environmental factors. Risk factors include being overweight, certain foods, some medications, and not drinking enough fluids. The diagnosis is usually based on symptoms, urine testing, and medical imaging. Blood tests may also be useful. Urinary stones are typically classified by their location in the kidney (nephrolithiasis), ureter (ureterolithiasis), or bladder (cystolithiasis), or by their chemical composition (calcium-containing, struvite, uric acid, or other compounds).
In those who have previously had stones, prevention is recommended by drinking fluids such that more than two liters of urine are produced per day. If this is not effective enough, thiazide diuretic, citrate or allopurinol may be taken. It is recommended that soft drinks containing phosphoric acid (typically colas) be avoided. When a stone causes no symptoms, no treatment is needed. For stones which are causing symptoms, pain control is usually the first measure, using medications such as nonsteroidal anti-inflammatory drugs or opioids. More severe cases may require procedures. For example, some stones can be shattered into smaller fragments using extracorporeal shock wave lithotripsy. Others require cystoscopic procedures.
In 2013, 49 million cases of kidney stones occurred, Resulting in about 15,000 deaths globally. In the United States, about 9% of the population had had a kidney stone. Generally, slightly more men are affected than women.