Kidney stone
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 (0.12 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 colic 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 anddilation of the kidney.
Most stones form due to a combination of genetics and environmental factors.[1] 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 theirchemical 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 is 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 (typicallycolas) 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 the United States about 9% of the population has had a kidney stone.Slightly more men are affected than women. In 2013 kidney stones resulted in about 15,000 deaths globally.
Signs and symptoms
The hallmark of a stone that obstructs the ureter or renal pelvis is excruciating, intermittent pain that radiates from the flank to the groin or to the inner thigh. This pain, known as renal colic, is often described as one of the strongest pain sensations known. Renal colic caused by kidney stones is commonly accompanied by urinary urgency, restlessness, hematuria, sweating, nausea, and vomiting. It typically comes in waves lasting 20 to 60 minutes caused by peristaltic contractions of the ureter as it attempts to expel the stone. The embryological link between the urinary tract, thegenital system, and the gastrointestinal tract is the basis of the radiation of pain to thegonads, as well as the nausea and vomiting that are also common in urolithiasis.Postrenal azotemia and hydronephrosis can be observed following the obstruction of urine flow through one or both ureters. Pain in the lower left quadrant can sometimes be confused with diverticulitis because the sigmoid colon overlaps the ureter and the exact location of the pain may be difficult to isolate due to the close proximity of these two structures.
Risk factors
Dehydration from low fluid intake is a major factor in stone formation.
High dietary intake of animal protein, sodium, refined sugars, fructose and high fructose corn syrup, oxalate,grapefruit juice, and apple juice may increase the risk of kidney stone formation.
Kidney stones can result from an underlying metabolic condition, such as distal renal tubular acidosis, Dent's disease,hyperparathyroidism, primary hyperoxaluria, or medullary sponge kidney. 3–20% of people who form kidney stones have medullary sponge kidney.
Kidney stones are more common in people with Crohn's disease; Crohn's disease is associated with hyperoxaluria and malabsorption of magnesium.
A person with recurrent kidney stones may be screened for such disorders. This is typically done with a 24-hour urine collection. The urine is analyzed for features that promote stone formation.
Calcite
Calcium is one component of the most common type of human kidney stones, calcium oxalate. Some studies suggest people who take calcium as a dietary supplement have a higher risk of developing kidney stones. In the United States, those findings were used] as the basis for setting the Reference Daily Intake for calcium in adults.
In the early 1990s, a study conducted for the Women's Health Initiative in the US found that postmenopausal women who consumed 1000 mg of supplemental calcium and 400 international units of vitamin D per day for seven years had a 17% higher risk of developing kidney stones than subjects taking a placebo. The Nurses' Health Study also showed an association between supplemental calcium intake and kidney stone formation.
Unlike supplemental calcium, high intakes of dietary calcium do not appear to cause kidney stones and may actually protect against their development. This is perhaps related to the role of calcium in binding ingested oxalate in the gastrointestinal tract. As the amount of calcium intake decreases, the amount of oxalate available for absorption into the bloodstream increases; this oxalate is then excreted in greater amounts into the urine by the kidneys. In the urine, oxalate is a very strong promoter of calcium oxalate precipitation—about 15 times stronger than calcium. A 2004 study found that diets low in calcium are associated with a higher overall risk for kidney stone formation. For most individuals, other risk factors for kidney stones, such as high intakes of dietary oxalates and low fluid intake, play a greater role than calcium intake.
Other electrolytes
Calcium is not the only electrolyte that influences the formation of kidney stones. For example, by increasing urinary calcium excretion, high dietary sodium may increase the risk of stone formation.
Drinking fluoridated tap water may increase the risk of kidney stone formation by a similar mechanism, though further epidemiologic studies are warranted to determine whether fluoride in drinking water is associated with an increased incidence of kidney stones. High dietary intake of potassium appears to reduce the risk of stone formation because potassium promotes the urinary excretion of citrate, an inhibitor of calcium crystal formation.
Kidney stones are more likely to develop, and to grow larger, if a person has low dietary magnesium. Magnesium inhibits stone formation.
Animal protein
Diets in Western nations typically contain a large proportion of animal protein. Consumption of animal protein creates an acid load that increases urinary excretion of calcium and uric acid and reduced citrate. Urinary excretion of excess sulfurousamino acids (e.g., cysteine and methionine), uric acid, and other acidic metabolites from animal protein acidifies the urine, which promotes the formation of kidney stones. Low urinary citrate excretion is also commonly found in those with a high dietary intake of animal protein, whereas vegetarians tend to have higher levels of citrate excretion. Low urinary citrate, too, promotes stone formation.
Vitamins
The evidence linking vitamin C supplements with an increased rate of kidney stones is inconclusive. The excess dietary intake of vitamin C might increase the risk of calcium oxalate stone formation, in practice this is rarely encountered. The link between vitamin D intake and kidney stones is also tenuous. Excessive vitamin D supplementation may increase the risk of stone formation by increasing the intestinal absorption of calcium; correction of a deficiency does not.
Other
There are no conclusive data demonstrating a cause-and-effect relationship between alcoholic beverage consumption and kidney stones. However, some have theorized that certain behaviors associated with frequent and binge drinking can lead to dehydration, which can in turn lead to the development of kidney stones.
The American Urological Association has projected that global warming will lead to an increased incidence of kidney stones in the United States by expanding the "kidney stone belt" of the southern United States.
People with lymphoproliferative/myeloproliferative disorders who were treated with chemotherapy developed symptomatic kidney stones 1.8% of the time in one study.
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