Kidney stones, or Renal calculi, are solid concretions (crystal aggregations) of dissolved minerals in urine; calculi typically form inside the kidneys or ureters. 
The terms nephrolithiasis and urolithiasis refer to the presence of calculi in the kidneys and urinary tract, respectively. Renal calculi can vary in size from as small as grains of sand to as large as grapefruit. Kidney stones typically leave the body by passage in the urine stream, and many stones are formed and passed without causing symptoms. If stones grow to sufficient size before passage — on the order of at least 2-3 millimeters — they can cause obstruction of the ureter. The resulting spasm of muscle, trying to move the stone, can cause severe episodic pain, most commonly felt in the flank, lower abdomen and groin (a condition called renal colic). Renal colic can be associated with nausea and vomiting due to the embyrological association of the kidneys and the intestinal tract. Hematuria is commonly present due to damage to the wall of the urethra as well as dysuria (when passing stones). Recurrence rates are estimated at about 10% per year.
The terms nephrolithiasis and urolithiasis refer to the presence of calculi in the kidneys and urinary tract, respectively. Renal calculi can vary in size from as small as grains of sand to as large as grapefruit. Kidney stones typically leave the body by passage in the urine stream, and many stones are formed and passed without causing symptoms. If stones grow to sufficient size before passage — on the order of at least 2-3 millimeters — they can cause obstruction of the ureter. The resulting spasm of muscle, trying to move the stone, can cause severe episodic pain, most commonly felt in the flank, lower abdomen and groin (a condition called renal colic). Renal colic can be associated with nausea and vomiting due to the embyrological association of the kidneys and the intestinal tract. Hematuria is commonly present due to damage to the wall of the urethra as well as dysuria (when passing stones). Recurrence rates are estimated at about 10% per year.Kidney stones can be due to underlying metabolic conditions, such as renal tubular acidosis, Dent's disease and medullary sponge kidney. Many centers will screen for such disorders in patients with recurrent kidney stones. However, most stones 
are idiopathic.
The most common type of kidney stone is composed of calcium oxalate crystals, and factors that promote the precipitation of crystals in the urine are associated with the development of these stones.
Conventional wisdom and common sense has long held that consumption of too much calcium can promote the development of kidney stones. However, current evidence suggests that the consumption of low-calcium diets is actually associated with a higher overall risk for the development of kidney stones. 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.
Other types of kidney stones are composed of struvite (magnesium, ammonium and phosphate); uric acid; calcium phosphate; and cystine.
The formation of struvite stones is associated with the presence of urea-splitting bacteria, most commonly Proteus mirabilis (but also Klebsiella, Serratia, Providencia species). These organisms are capable of splitting urea into ammonia, decreasing the acidity of the urine and resulting in favorable conditions for the formation of struvite stones.
The formation of uric acid stones is associated with conditions that cause high blood uric acid levels, such as gout, leukemias/lymphomas treated by chemotherapy (secondary gout from the death of leukemic cells), and acid/base metabolism disorders.
The formation of calcium phosphate stones is associated with conditions such as hyperparathyroidism and renal tubular acidosis.
The formation of cystine stones is uniquely associated with people suffering from cystinuria, who accumulate cystine in their urine.
Clinical presentation and diagnosis
Symptoms of kidney stones include:
Colicky Pain: "loin to groin". Described to be the worst pain ever felt.
Hematuria: due to damage to wall of ureter and/or urethra
Dysuria: when passing stones
Oliguria: obstruction of bladder or urethra by stone, or exremely rarely, simultaneouus obstruction of both ureters by a stone.
Nausea/vomiting: embryological link with intestine — stimulates vomiting center
Diagnosis is usually made on the basis of the location and severity of the pain, which is typically colic in nature (comes and goes in spasmodic waves). Radiological imaging is used to confirm the diagnosis and a number of other tests can be undertaken to help establish both the possible cause and consequences of the stone. Ultrasound imaging is also useful as it will give details about the presence of hydronephrosis (swelling of the kidney - suggesting the stone is blocking the outflow of urine). It can also be used to show the kidneys during pregnancy when standard x-rays are discouraged. About 10% of stones do not have enough calcium to be seen on standard x-rays (radiolucent stones) and may show up on ultrasound although they typically are seen on CT scans.
The relatively dense calcium renders these stones radio-opaque and they can be detected by a traditional X-ray of the abdomen that includes Kidneys, Ureters and Bladder—KUB. This may be followed by an IVP (Intravenous Pyelogram; IntraVenous Urogram (IVU) is the same test by another name) which requires about 50ml of a special dye to be injected into the bloodstream that is excreted by the kidneys and by its density helps outline any stone on a repeated X-ray. These can also be detected by a Retrograde pyelogram where similar "dye" is injected directly into the ureteral opening in the bladder by a surgeon, usually a urologist. Computed tomography (CT or CAT scan), a specialized X-ray, is considered the gold-standard diagnostic test for the detection of kidney stones, and in this setting does not require the use of intravenous contrast, which carries some risk in certain people (eg, allergy, kidney damage). All stones are detectable by CT except very rare stones composed of certain drug residues in urine. The non-contrast "renal colic study" CT scan has become the standard test for the immediate diagnosis of flank pain typical of a kidney stone. If positive for stones, a single standard x-ray of the abdomen (KUB) is recommended. This additional x-ray provides the physicians with a clearer idea of the exact size and shape of the stone as well as its surgical orientation. Further, it makes it simple to follow the progress of the stone without the need for the much more expensive CT scan just by doing another single x-ray at some point in the future.
Investigations typically carried out include:
Microscopic study of urine, which may show proteins, red blood cells, pus cells, cellular casts and crystals.
Culture of a urine sample to exclude urine infection (either as a differential cause of the patient's pain, or secondary to the presence of a stone)
Blood tests: Full blood count for the presence of a raised white cell count (Neutrophilia) suggestive of infection, a check of renal function and if raised blood calcium blood levels (hypercalcaemia).
24 hour urine collection to measure total daily urinary volume, magnesium, sodium, uric acid, calcium, citrate, oxalate and phosphate.
are idiopathic.The most common type of kidney stone is composed of calcium oxalate crystals, and factors that promote the precipitation of crystals in the urine are associated with the development of these stones.
Conventional wisdom and common sense has long held that consumption of too much calcium can promote the development of kidney stones. However, current evidence suggests that the consumption of low-calcium diets is actually associated with a higher overall risk for the development of kidney stones. 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.
Other types of kidney stones are composed of struvite (magnesium, ammonium and phosphate); uric acid; calcium phosphate; and cystine.
The formation of struvite stones is associated with the presence of urea-splitting bacteria, most commonly Proteus mirabilis (but also Klebsiella, Serratia, Providencia species). These organisms are capable of splitting urea into ammonia, decreasing the acidity of the urine and resulting in favorable conditions for the formation of struvite stones.
The formation of uric acid stones is associated with conditions that cause high blood uric acid levels, such as gout, leukemias/lymphomas treated by chemotherapy (secondary gout from the death of leukemic cells), and acid/base metabolism disorders.
The formation of calcium phosphate stones is associated with conditions such as hyperparathyroidism and renal tubular acidosis.
The formation of cystine stones is uniquely associated with people suffering from cystinuria, who accumulate cystine in their urine.
Clinical presentation and diagnosis
Symptoms of kidney stones include:
Colicky Pain: "loin to groin". Described to be the worst pain ever felt.
Hematuria: due to damage to wall of ureter and/or urethra
Dysuria: when passing stones
Oliguria: obstruction of bladder or urethra by stone, or exremely rarely, simultaneouus obstruction of both ureters by a stone.
Nausea/vomiting: embryological link with intestine — stimulates vomiting center
Diagnosis is usually made on the basis of the location and severity of the pain, which is typically colic in nature (comes and goes in spasmodic waves). Radiological imaging is used to confirm the diagnosis and a number of other tests can be undertaken to help establish both the possible cause and consequences of the stone. Ultrasound imaging is also useful as it will give details about the presence of hydronephrosis (swelling of the kidney - suggesting the stone is blocking the outflow of urine). It can also be used to show the kidneys during pregnancy when standard x-rays are discouraged. About 10% of stones do not have enough calcium to be seen on standard x-rays (radiolucent stones) and may show up on ultrasound although they typically are seen on CT scans.
The relatively dense calcium renders these stones radio-opaque and they can be detected by a traditional X-ray of the abdomen that includes Kidneys, Ureters and Bladder—KUB. This may be followed by an IVP (Intravenous Pyelogram; IntraVenous Urogram (IVU) is the same test by another name) which requires about 50ml of a special dye to be injected into the bloodstream that is excreted by the kidneys and by its density helps outline any stone on a repeated X-ray. These can also be detected by a Retrograde pyelogram where similar "dye" is injected directly into the ureteral opening in the bladder by a surgeon, usually a urologist. Computed tomography (CT or CAT scan), a specialized X-ray, is considered the gold-standard diagnostic test for the detection of kidney stones, and in this setting does not require the use of intravenous contrast, which carries some risk in certain people (eg, allergy, kidney damage). All stones are detectable by CT except very rare stones composed of certain drug residues in urine. The non-contrast "renal colic study" CT scan has become the standard test for the immediate diagnosis of flank pain typical of a kidney stone. If positive for stones, a single standard x-ray of the abdomen (KUB) is recommended. This additional x-ray provides the physicians with a clearer idea of the exact size and shape of the stone as well as its surgical orientation. Further, it makes it simple to follow the progress of the stone without the need for the much more expensive CT scan just by doing another single x-ray at some point in the future.
Investigations typically carried out include:
Microscopic study of urine, which may show proteins, red blood cells, pus cells, cellular casts and crystals.Culture of a urine sample to exclude urine infection (either as a differential cause of the patient's pain, or secondary to the presence of a stone)
Blood tests: Full blood count for the presence of a raised white cell count (Neutrophilia) suggestive of infection, a check of renal function and if raised blood calcium blood levels (hypercalcaemia).
24 hour urine collection to measure total daily urinary volume, magnesium, sodium, uric acid, calcium, citrate, oxalate and phosphate.
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