What are stones?
Stones are hard masses that form in the urinary tract and may cause pain, bleeding, or an infection or block of the flow of urine. Stones are made of minerals in the urine that form crystals. Sometimes the crystals grow into stones. About 85% of the stones are composed of calcium, and the remainder are composed of various substances, including uric acid, cystine, or struvite. Struvite stones are a mixture of magnesium, ammonium, and phosphate. They are also called infection stones, because they form only in urine that is infected. 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.
Stones may form if the urine becomes too saturated with salts that can form stones or because the urine lacks the normal inhibitors of stone formation.
Stones are more common among people with certain disorders (for example, hyperparathyroidism, dehydration, and renal tubular acidosis), and among individuals with a diet very high in animal-source protein or vitamin C or who do not consume enough water or calcium. Individuals with a family history of stone formation are more likely to have calcium stones and to have them more often. Individuals 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, 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.