Kidney stones result from stones or renal calculi in the ureter. The stones are solid concretions or calculical formed in the kidneys from dissolved urinary minerals.
Kidney stones result from stones or renal calculi in the ureter. The stones are solid concretions or calculical formed in the kidneys from dissolved urinary minerals. Nephrolithiasis refers to the condition of having kidney stones. Urolitiasis refers to the condition of having calculi in the urinary tract, which may form or pass into the urinary bladder. ureterolithiasis is the condition of having a calculus in the ureter, the tube connecting the kidneys and the bladder. The term bladder stones usually applies to urolithiasis of the bladder in non-human animals such as dogs and cats.
Calyceal calculi refer to aggregations in either the minor or major calyx, parts of the kidney which pass urine into the ureter.
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 (usually at least 2-3 millimeters), they can cause obstruction of the ureter. The resulting obstruction causes dilation or stretching of the upper ureter and renal pelvis (the part of the kidney where the urine collects before entering the ureter) as well as muscle spasm of the ureter, trying to move the stone. This leads to 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. There can be blood in the urine, visible with the naked eye or under the microscope due to damage to the lining of the urinary tract .
There are several types of kidney stones based on the type of crystals of which they consist. The majority are calcium oxalate stones, followed by calcium phospha stones. More rarely, struvite stones are produced by urea-splitting bacteria in people with urinary tract infections, and people with certain metabolic abnormalities may produce uric acid stones or cysteine stones.
The diagnosis of a kidney stone can be confirmed by radiological studies and/or ultrasound examination, urine tests and blood tests are also commonly performed.
Signs and symptoms
Symptoms of kidney stones include:
Colicky pain : "loin to groin". Often described as "the worst pain ever experienced." This can also occur in the lower back The pain is elicited by contractions of the ureter in response to the stone, causing severe, crampy pain in the flank or lower back, often radiating to the groin or, in men, to the testes The pain typically comes in waves, with a typical wave lasting 20 to 60 minutes.
- Nausea/ vomiting:.
- hemeturia: blood in the urine, due to minor damage to inside wall of kidney, ureter and/or urethra.
- pyuria: pus in the urine.
- dysuria: burning on urination when passing stones (rare). More typical of infection.
- oliguria: reduced urinary volume caused by obstruction of the bladder or urethra by stone, or extremely rarely, simultaneous obstruction of both ureters by a stone.
- Postrenal azotemia: the blockage of urine flow through a ureter.
Kidney stones do not have a single, well-defined cause, but are the result of a combination of factors. A stone is created when the urine does not have the correct balance of fluid and a combination of minerals and acids. When the urine contains more crystal-forming substances than the fluid can dilute, crystals can form. Normally the urine contains components that prevent these crystals from attaching to each other. However, when these substances fall below their normal proportions, stones can form out of an accumulation of crystals.
There has been some evidence that water fluoridation may increase the risk of kidney stone formation. In one study, patients with symptoms of skeletal fluorosisskeletal were 4.6 times as likely to develop kidney stones.
A 1998 paper in the archives of internal medicine examined the sources of a widely-held belief in the medical community that vitamin C can cause kidney stones, and found it to be based on several circular references, ultimately attributing the belief to a wider pattern of skepticism regarding efficacy of vitamin supplements A more recent study suggested a causal relationship may exist, but it was not conclusive.
Calcium oxalate stones
The most common type of kidney stone is composed of Calcium oxalate crystals, occurring in about 75 to 80% of cases, and the factors that promote the precipitation of crystals in the urine are associated with the development of these stones.
Perhaps counter-intuitively, current evidence suggests that the consumption of diets low in calcium is associated with a higher overall risk for the development of kidney stone 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.
Uric acid (urate)
About 5–10% of all stones are formed from uric acid . A risk factor is obesity. Uric acid stones form in association with conditions that cause hyperuricosuria with or without high blood serum uric acid levels and with acid/base metabolism disorders where the urine is excessively acidic resulting in uric acid precipitation. A diagnosis of uric acid nephrolithiasis is supported if there is a radiolucent stone, a persistent undue urine acidity, and uric acid crystals in fresh urine samples. .
Preventive strategies may include dietary modifications and medication with the goal of reducing excretory load on the kidneys
Drinking enough water to make 2 to 2.5li urine per day. A failure to intake sufficient liquids will mean the urine is concentrated and the substances that create kidney stones are more likely to clump together.
- A diet low in protein The National Institutes of website disputes the notion that specific foods can cause formation of kidney stones in everyone, although "in some people, a diet high in protein may lead to kidney stones because extra protein causes calcium to be excreted from the body, raising calcium levels in the urine
People with urinary tract infections, kidney disorders such as cystic kidney diseases, and certain rare, inherited metabolic disorders are also more likely to develop kidney stones. In some of these susceptible people, the foods they eat can have an influence on the development of their kidney stones. Prevention strategies include:
- Restriction of oxalate , or consumption of more calcium .
- Some fruit juices, such as orange, blackcurrant, and cranberry, may be useful for lowering the risk factors for specific types of stones. Orange juice may help prevent calcium oxalate stone formation, blackcurrant may help prevent uric acid stones, and cranberry may help with UTI-caused stones. Lemons have the highest concentration of citrate of any citrus fruit, and daily consumption of lemonade has been shown to decrease the rate of stone formation. Beer is also recommended, but grapefruit juice has been known to increase the risk of stones.
- One study indicated that intake of caffeinated beverages increases risk of kidney stones, a finding which was soon taken up in the popular press. While it may be advised to avoid cola beverages, whether artificially sweetened or not because of their high phosphate content, this does not include coffee or tea. Prospective cohort studies of coffee and tea actually indicate that they may prevent kidney stones, while apple juice and grapefruit juice may cause them. Avoiding large doses of vitamin C.
- In South Asia, there is a popular cultural belief that spinach should not be cooked along with tomatoes, since spinach is rich in calcium and oxalates, and reacts with the chemicals in tomatoes, causing deposits in those prone to kidney stone formation. However, this theory is not scientifically proven and is controversial]
For those patients interested in optimizing their kidney stone prevention options, a 24 hour urine test can be a useful diagnostic]
Diuretics (dietary and medicinal)
Although it has been claimed that the diuretic effects of alcohol can result in dehydration, which is important for kidney stone sufferers to avoid, there are no conclusive data demonstrating any cause and effect regarding kidney stones. However, some have theorized that frequent and binge drinkers create situations that set up dehydration: alcohol consumption, hangovers, and poor sleep and stress habits. In this view, it is not the alcohol that creates a kidney stone but it is the alcohol drinker's associated behavior that sets it up.
One of the recognized medical therapies for prevention of stones is thiazides, a class of drugs usually thought of as diuretics. These drugs prevent calcium stones through an effect independent of their diuretic properties: they reduce urinary calcium excretion. Nonetheless, their diuretic property does not preclude their efficacy as stone preventive. Sodium restriction is necessary for clinical effect of thiazides, as sodium excess promotes calcium excretion. Thiazides work best for renal leak hypercalciuria - a condition in which the high urinary calcium levels are from a primary kidney defect. They work well initially for absorptive hypercalciuria - a condition in which high urinary calcium is a result of excess absorption from the GI tract. With this condition they lose effectiveness over time, typically around 2 years, and patients need a period off treatment to regain effectiveness. Thiazides will cause hypokalemia and reduced urinary citrate levels so should be given with supplements for each, usually as a potassium citrate preparation.
Though does caffeine acutely increase urinary calcium excretion, several independent epidemiologic studies have shown that coffee intake overall is protective against the formation of stones.
Reduction of calcium or oxalates in diet
Since oxalates form the basis of one type of kidney stone, one prevention strategy is to restrict consumption of oxalate-rich foods such as chocolate, nuts, soyabeans, rhubarb, and spinach. However, this is only helpful in those patients who are absorbing excess oxalate - a minority of patients as most oxalate excreted in the urine is actually made by the liver.[
Stones are formed when oxalates bind with calcium, but calcium plays a vital role in body chemistry and limiting calcium may be unhealthy. Recent research has actually shown that a diet that includes recommended calcium levels prevents kidney stones in men better than a low-calcium diet appears to. Since calcium in the intestinal tract will bind with available oxalate, thereby preventing its absorption into the blood stream, some nephrologists and urologists recommend chewing calcium tablets during meals containing oxalate foods. Calcium citrate should be taken with food if dietary calcium cannot be increased.
Measurements of food oxalate content have been difficult and issues remain about the proportion of oxalate that is bio-available, versus a proportion that is not absorbed by the intestine. Oxalate-rich foods are usually restricted to some degree, particularly in patients with high urinary oxalate levels, but no randomized controlled trial of oxalate restriction has been performed to test that hypotheses.
Reduction of animal-protein in diet
Diets in Western nations typically contain more animal-protein than the body needs, and as the excess amino acids are broken down and excreted, the sulfurous amino acids (typically derived from animal rather than vegetarian foods) cause calcium to be excreted in the urine; calcium is one component of the most common type of human kidney stones, calcium oxalate. Red meat also contains acids that need to be excreted and this acidity constitutes another risk factor for kidney stones.
In either case, the body often balances this acidic urinary pH by leaching calcium (an alkaline pH-factor) from the bones.
Excess animal-protein also causes more uric acid to be excreted, increasing the risk of stones in which uric acid instead of calcium is a component of the kidney stone.