Tiny stones may cause no symptoms, but larger stones can cause excruciating pain in the area between the ribs and hips in the back.
Usually, an imaging test and an analysis of urine are done to diagnose stones.
Sometimes stone formation can be prevented by changing the diet or increasing fluid intake.
Stones that do not pass on their own are removed with lithotripsy or an endoscopic technique.
Urinary tract stones begin to form in a kidney and may enlarge in a ureter or the bladder. Depending on where a stone is located, it may be called a kidney stone, ureteral stone, or bladder stone. The process of stone formation is called urolithiasis, renal lithiasis, or nephrolithiasis.
Every year, about 1 of 1,000 adults in the United States is hospitalized because of stones in the urinary tract. Stones are more common among middle-aged and older adults and men. Stones vary in size from too small to be seen with the naked eye to 1 inch (2.5 centimeters) or more in diameter. A large, so-called staghorn (because of its many projections that resemble a deer's antlers), stone may fill almost the entire renal pelvis (the central collecting chamber of the kidney) and the tubes that drain into it (calices).
Inside the Kidney
A urinary tract infection may result when bacteria become trapped in urine that pools above a blockage. When stones block the urinary tract for a long time, urine backs up in the tubes inside the kidney, causing excessive pressure that can cause the kidney to swell (hydronephrosis—see Hydronephrosis: A Distended Kidney) and eventually damage it.
Stones may form because the urine becomes too saturated with salts that can form stones or because the urine lacks the normal inhibitors of stone formation. Citrate is such an inhibitor because it normally binds with calcium that is often involved in forming stones.
Stones are more common among people with certain disorders (for example, hyperparathyroidism, dehydration, and renal tubular acidosis) and among people whose diet is very high in animal-source protein or vitamin C or who do not consume enough water or calcium. People who have a family history of stone formation are more likely to have calcium stones and to have them more often. People who have undergone surgery for weight loss (bariatric surgery) may also be at increased risk of stone formation.
Rarely, drugs (including indinavir) and substances in the diet (such as melamine) cause stones.
Stones, especially tiny ones, may not cause any symptoms. Stones in the bladder may cause pain in the lower abdomen. Stones that obstruct the ureter or renal pelvis or any of the kidney’s drainage tubes may cause back pain or renal colic. Renal colic is characterized by an excruciating intermittent pain, usually in the area between the ribs and hip, that spreads across the abdomen and often extends to the genital area. The pain tends to come in waves, gradually increasing to a peak intensity, then fading, over about 20 to 60 minutes. The pain may radiate down the abdomen toward the groin or testis or vulva.
Other symptoms include nausea and vomiting, restlessness, sweating, and blood or a stone or a piece of a stone in the urine. A person may have an urge to urinate frequently, particularly as a stone passes down the ureter. Chills, fever, burning or pain during urination, cloudy, foul-smelling urine, and abdominal swelling sometimes occur.