Kidney Stones

Kidney stones can be composed of different substances, but the most common ones (80% of stones) consist of calcium salts, mostly in the form of calcium oxalate and calcium phosphate.^[1] Less common kidney stones may form from other substances such as medications, struvite, uric acid, or cystine.^[2] Kidney stones tend to occur more frequently in men, with an incidence of 10% compared to 5% in women.^[3][4]

When a stone is dislodged from the kidney and enters the ureter (the tube that connects the kidney to the bladder), it often causes significant pain by irritating the urether, and sometimes by blocking the normal flow of urine. While most stones pass on their own, they may also block the urinary tract, requiring treatment or surgery for removal. (Most stones are small, <6mm, and pass on their own; larger stones tend to require procedures for removal.)

One of the main symptoms of kidney stones is reno-ureteral colic, or “renal colic”, a sudden pain somewhere in the area along the route of the ureter (from the flank/mid-back to the lower abdomen) that is usually caused by the irritation of the ureter (causing spasm) and/or obstruction blocking the flow of urine from the kidney to the bladder.^[5]

Additional symptoms that people with kidney stones may experience include the following:^[6]

• Burning sensation during urination
• Nausea and/or vomiting
• Changes in urine (presence of blood, cloudy, or foul-smelling)

Some people with kidney stones may have no symptoms at all.

Although acute pain in the kidney area is a common symptom, diagnosis of kidney stones can only be confirmed from the observation of an actual stone, which may be detected after passing through the urinary tract, with imaging tests, or during surgery. When kidney stones are suspected, a physician will first obtain a detailed medical history and perform a physical exam. Imaging tests such as ultrasound or computerized tomography (CT) may be used to examine the urinary tract for the presence of stones.^[7][8] X-ray imaging may also be used, but is more often used in follow-up care,^[9] due to its more limited ability to detect smaller stones.^[10]

To treat pain associated with kidney stones, non-steroidal anti-inflammatory drugs (NSAIDs) are the main treatment, but opioids may be used if NSAIDs aren’t effective for relieving pain.^[11]

Treatment of the stones themselves has evolved over the past 30 years, from removal by open surgery to treatment with less invasive methods.

These are the three main treatments for kidney stones in current use:^[5]

Extracorporeal shock wave lithotripsy (SWL): SWL, or “lithotripsy,” is a non-invasive treatment that targets stones with powerful ultrasound waves, causing them to break into small enough fragments to pass through the urinary tract along with the urine.^[12]

Uteroscopic procedures: A urologist will insert a small scope into the urinary tract to locate the stone, and remove via a small wire basket that latches onto and grabs the stone. If the stone is too large for removal or can’t be dislodged from its location, a stent may be placed in the ureter to encourage the stone to pass, or it may instead be broken into tiny pieces with a laser, sound waves, or electrical energy.^[13]

Percutaneous nephrolithotomy (PCNL): PCNL is a surgical procedure that involves the insertion of an endoscope through a small incision in the skin into the kidney. The procedure is performed under general anesthesia and is generally used in cases when stones are large(> 2 cm) in size.^[14]

Many of the studies on the effects of supplements on kidney stones have focused on the impact of supplementation on the risk of developing stones. Vitamin C has been studied frequently, since it’s converted to oxalate after ingestion and excreted via the urine, which could potentially promote stone formation by increasing oxalate levels in the urine. A couple of studies found a high vitamin C intake was associated with an increased risk of kidney stone risk in men.^[15][16] An additional study found evidence that a high intake of vitamin C from supplements was likely responsible for the increased kidney stone risk in men.^[17] Other notable supplements that have been studied for their effect on kidney stones include caffeine,^[18] calcium, and vitamin D.^[19]

In people who are prone to getting kidney stones, dietary factors can play a role in the risk of developing stones.^[20]

Specific types of diets have also been studied for their potential effect on kidney stone risk. Low-carbohydrate, high-protein diets such as the Atkins diet may have a detrimental effect on urine composition (e.g., higher urinary calcium and uric acid, lower urinary citrate levels), potentially increasing the risk of forming kidney stones.^[21][22]

In contrast, the DASH diet^[23] and Mediterranean-style diets^[24] have been associated with reduced risk of developing kidney stones.

Note that many of the observational studies on diet and kidney stones examine the association between diets and any type of kidney stone. There are also specific dietary recommendations for preventing kidney stones depending on the type.

Medication may be prescribed by a physician to help kidney stones pass. Alpha-adrenergic receptor blockers, such as tamsulosin,^[25][26] and calcium channel blockers^[25] cause dilation of the urethra, which increases the chance of stones passing on their own.

If kidney stones continue to be a recurring problem for people following all of the recommended dietary guidelines, then pharmaceutical treatments may also be an option for prevention.^[5] Thiazide diuretics have shown some efficacy in preventing calcium kidney stones in people with normal urine calcium levels.^[27] Drugs such as allopurinol or febuxostat, which reduce uric acid levels, may be helpful for preventing uric acid kidney stones in people with high levels of uric acid in their urine. ^[28] Treatment with citrate (from potassium citrate), which inhibits the formation of calcium crystals,^[29] has also shown some efficacy for preventing stones in randomized controlled trials.^[30][31]

All compounds dissolved in aqueous solution have a threshold concentration at which they are no longer soluble. When this concentration is exceeded, the molecules become supersaturated, at which point they begin to form insoluble crystals. Calcium oxalate, a soluble salt forming the most common type of kidney stones, becomes supersaturated at higher concentrations, forming stones that accumulate in the kidneys or urinary tract.^[32]