what causes kidney stones

Kidney stones are composed of insoluble salts that are normally dissolved in urine, such as calcium, oxalate, uric acid, and cystine.

There are different types of kidney stones (nephrolithiasis), including calcium oxalate, calcium phosphate, and uric acid stones. Small stones in the urinary tract can pass through the urinary system without requiring any treatment. However, bigger stones can get stuck in the ureters (tubes that move urine from the kidneys to the bladder) and block the flow of urine. Symptoms of kidney stones include intense abdominal pain, blood in urine, pain on urination, increased urinary frequency, nausea, and vomiting.

The prevalence and incidence of kidney stones are increasing globally; on average, one in 11 individuals in the United States develop kidney stones at least once in their lifetime.

What causes kidney stones?

Kidney stones develop due to genetic and environmental factors and can occur at any age. Individuals with a positive family history or low fluid intake are at risk of developing kidney stones. Kidney stones can form as a result of various dietary, non-dietary, and urinary risk factors.

Calcium oxalate

A key risk factor for kidney stone formation is high levels of calcium in urine or a low calcium intake. Calcium oxalate and calcium phosphate stones are the most common types of urinary tract stones. Dairy products and calcium supplements can help reduce the risk of kidney stones caused by diminished calcium consumption.

High amounts of oxalate in urine or a high oxalate intake can increase the risk of calcium oxalate stones. Foods rich in oxalate include tea, spinach, okra, rhubarb, chocolate, and sweet potatoes. Individuals with high levels of urinary oxalate should avoid high-dose vitamin C supplements to reduce production of endogenous oxalate. Additionally, increasing consumption of alkaline-rich foods, such as fruits and vegetables, may be beneficial since citrate is a natural inhibitor of kidney stones.

Urinary tract infections

Recurrent urinary tract infections can lead to the development of a struvite. Urease is found in various bacteria, most commonly Proteus mirabilis, and is therefore produced in patients with frequent urinary tract infections. The urease enzyme is necessary to split urea into ammonia and carbon dioxide, increasing the alkalinity of urine. This increase in pH causes phosphate to precipitate onto the insoluble ammonia, forming struvite stones. Surgery is the main method of treatment of struvite stones.

Uric acid

Uric acid stones can occur due to a diet high in purines, particularly from a high intake of animal protein. This results in an excessive amount of uric acid in the urine, a low urine volume, and low urinary pH. Unlike the other types of kidney stones, uric acid stones are more common in men than in women. Since uric acid stones form in acidic environments, patients should increase their consumption of alkaline-rich foods.

Environmental reasons

A hot and arid climate may have an influence on causing kidney stones due to excessive fluid loss from sweating. It has been predicted that the incidence of renal stones may increase from 40% to 56% by 2050 as a consequence of global warming.

Medical conditions

A number of medical conditions have been found to increase the risk of developing kidney stones, including obesity, diabetes, hypertension, chronic kidney disease, and cardiovascular problems.

Individuals who are overweight, obese, or have a high fructose consumption have been demonstrated to be at high risk for kidney stone formation.

Treatment and prevention

A CT scan can be used to confirm the presence of kidney stones. Treatment includes pain management, hydration, and removal of the renal stones through endoscopic stone removal or extracorporeal shockwave lithotripsy (which uses sound waves to fragment the stones).

Regardless of the cause, once kidney stones have been identified and removed, the next step is to consider how to prevent them from reoccurring. Preventing kidney stones involves drinking enough fluids, having a balanced diet, taking calcium and citrate supplements, and adopting a healthy lifestyle. Please consult a doctor if you are experiencing symptoms of kidney stones.

Written by Albina Babu, MSc

References:

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Aggarwal, R., et al. (2017). Renal stones: a clinical review. EMJ Urol, 5(1), pp.98-103.

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Taylor, E.N., Stampfer, M.J. and Curhan, G.C. (2005). Obesity, weight gain, and the risk of kidney stones. Jama, 293(4), pp.455-462.

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Gul, Z. and Monga, M. (2014). Medical and dietary therapy for kidney stone prevention. Korean Journal of Urology, 55(12), pp.775-779.

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