Kidney stones. Overview, incidence, causes and risk factors.
The occurrence of kidney stones, which is also referred to as  nephrolithiasis, renal calculi or urolithiasis is a pathological condition. A kidney stone is a crystalloid formation created due to the prolonged
presence
and excessive concentration of mineral salts in the urine. The chemical character of kidney stones varies, depending on whether they are consisted from calcium oxalate, magnesium ammonium phosphate (struvite), sodium urate or cystine. The very former type is the most common, representing more than 70% of the clinical cases.
The size, shape and color of a kidney stone may vary widely. It can be as small as a grain of sand or as large as an orange. The edges can be either smooth and rounded, or moderately uneven. In some cases they may be very sharp or thorny (coral-like stones). The color ranges from yellow to dark brown.
The stones are produced within the kidney but they can be found throughout the urinary track, since in many cases they tend to come through and be excreted with urine. Quite often, a kidney stone has to be removed, when it is located in the ureter and more rarely in the bladder.
In general, kidney stone do not lead to complications. However, in some cases it can result in hydronephrosis, which is the distention of the kidney. This situation if not diagnosed and treated in time, can potentially cause failure of the organ.
Incidence of kidney stones.
Males are far more
susceptible
to kidney stones. Epidemiologic studies have shown that 75% of the sufferers are men. However, there is no evidence that hormonal differences between genders are associated with kidney stones development. Ethnicity and in general hereditary factors seem to be important. It is well acknowledged that nephrolithiasis runs in families, whereas Afro-Americans are less susceptible to this.
The most likely ages for kidney stones to occur are between thirty and sixty.
Causes and risk factors for kidney stones.
Calcium oxalate kidney stones. The prolonged excessive presence of calcium and oxalic acid in the urine is the major cause for the development of nephrolithiasis, since calcium oxalate kidney stones are the most common.
 People presenting excessive absorption of calcium within the gastrointestinal track or sufferers from hyperparathyroidism, sarcoidosis, inflammatory bowel disease, chronic metabolic acidosis and chronic reduced urination are candidates to develop calcium oxalate kidney stones. Females suffering from osteoporosis can potentially develop this kind of kidney stones, as well. Sedentary lifestyle can increase the risk for calcium oxalate kidney stones to occur.
Apart from hereditary and other underlying pathological factors, diet can play an important role in the formation of calcium oxalate kidney stones.
High daily consumption of dietary salt is an important risk factor. Sodium, which is contained in salt, tends to increase the excretion of calcium in the urine (hypercalciuria).
Studies have shown that too regular intake of complete protein can elevate the risk for calcium oxalate kidney stones formation.
Hypervitaminosis D is a major cause of increased amounts of calcium in urine and can lead to development of kidney stones.
It has been acknowledged foods that their metabolism results in oxalate production should be eaten in moderation by people with calcium oxalate kidney stones history. For more information see the Dietary Prevention of Kidney Stones page.
Struvite kidney stones. These are the second most common kidney stones, since they represent the 10% of nephrolithiasis cases. Females are more susceptible to struvite kidney stones.
Struvite kidney stones are consisted from magnesium ammonium phosphate crystals and they typically occur as a complication of conditions, like neurogenic bladder and persistent urinary tract infections caused by a variety of bacteria, including Proteus, Escherichia coli, Staphylococcus, Pseudomonas, Providencia and Klebsiella.
Uric acid kidney stones. They are found in 5- 8% of nephrolithiasis cases and occasionally they may coexist with calcium oxalate kidney stones. People who suffer from gout and hyperuricosuria or patients under chemotherapy and others that have undergone liver transplantation are likely to present uric acid kidney stones. Conditions that can cause prolonged dehydration, such as chronic diarrhoeic diseases may lead to uric acid kidney stones too.
The kidney stones occur due to increased concentrations of uric acid and low pH in the urine. Uric acid is a waste product occurring from the metabolism of protein and it is excreted through the kidneys. When the acidity in the urine increases, the contained uric acid gets insoluble and precipitates, resulting in crystals and eventually in kidney stones formation.
Cystine kidney stones. These are rare, occurring in no more than 1% of nephrolithiasis cases. Cystine kidney stones development is a complication of an inherited tubular transport disorder, which involves reduced utilization, for a number of amino acids, including cystine. The latest is an amino acid that is used among others in protein synthesis within the body. If cystine is not metabolized properly, it is found in abundance in urine (cystinuria). When the concentration reaches the critical point, the amino acid precipitates creating insoluble crystals and kidney stones.
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