What are kidney stones?

Kidney stones^[1], also called renal lithiasis or nephrolithiasis, are hard deposits that form inside the kidneys. There are many causes for kidney stones, and they can occur in any part of the urinary tract—from the kidneys to the bladder. These stones are made of minerals and salts. They usually occur when an excess of these waste materials becomes concentrated in the urine and crystallizes into small stones. When they are found early on, kidney stones usually don’t cause permanent damage. However, passing kidney stones from the body can be extremely painful. There are various treatments for kidney stones, ranging from preventive treatment (if you have had kidney stones and are at risk of developing them again) to pain management.

How common are kidney stones?

About 10% of the population^[2] will have a kidney stone during their lifetime. Of those patients, roughly 25% have a family history of kidney stones, indicating the role of genetics in the condition. According to the National Kidney Foundation, more than 500,000 people^[3] go to emergency rooms for kidney stone problems every year. If preventive measures aren’t taken, about half^[4] of people who have had kidney stones will have one or more again within 10–15 years. Men are at greater risk for developing kidney stones^[5] than women: the lifetime risk is about 19% for men and 9% for women. Having other diseases like high blood pressure, diabetes, or obesity may increase your risk of developing kidney stones.

What causes kidney stones?

As their name implies, kidney stones occur in the kidneys. The urinary tract is made up of three structures: the kidneys, ureters (ducts through which urine travels to the bladder), and the bladder (a hollow organ that stores urine from the kidneys before being disposed of through urination). This system’s job is to make, transport, and store urine and to filter wastes from the body. Most people have two kidneys^[6]. The kidneys are fist-sized organs found on each side of the spine behind the liver, stomach, pancreas, and intestines. The kidneys filter wastes from the blood, which is then removed from the body in your urine. These organs help control the levels of sodium, potassium, and calcium in your blood. Oftentimes, kidney stones don’t have one single, definite cause^[7]. They can form when the urine contains more crystal-forming minerals and waste products (like calcium, oxalate, and uric acid) than the fluid in the urine can dilute. Kidney stones can also form when the urine lacks substances that prevent crystals from sticking together. This makes it much easier for waste products to crystallize, leading to kidney stones. Sometimes, kidney stones can move from the kidney and get stuck in the ureter. When this occurs, it is known as a ureteral stone.

Types of kidney stones

There are multiple types^[8] of kidney stones. Understanding the type of kidney stone you have can help determine its cause and provide insight into how you can prevent getting more kidney stones in the future. Types of kidney stones include:

• Calcium stones (80% of stones): Calcium stones are the most common kidney stones. There are two types of calcium stones: calcium oxalate and calcium phosphate.

Calcium oxalate, which occurs when an excess of calcium and oxalate builds up in the urine, is by far the most common form of calcium stone. Oxalate is a naturally occurring substance made daily by your liver. It is also found in food: some fruits, vegetables, nuts, and chocolate have a high content of oxalate. Along with a high-oxalate diet, high doses of vitamin C, intestinal bypass surgery, and severe metabolic disorders can increase the concentration of calcium or oxalate in the urine. The other form of calcium stones, calcium phosphate, is much more common in people with metabolic conditions, such as renal tubular acidosis. Calcium phosphate stones have also been linked to certain migraine headaches and certain seizure medications, such as the anticonvulsant topiramate (generic Topamax).

• Struvite infection/struvite stones (10% of stones): Struvite kidney stones are much less common than calcium stones. They form in response to bacterial infections like urinary tract infections (UTIs). Certain bacteria can make the urine less acidic and more basic, or alkaline. Struvite stones form in alkaline urine. They are frequently large and fast-growing with branch-like structures.

People who get chronic UTIs are at the highest risk of developing struvite kidney stones.

• Uric acid stones (5–10% of stones): Some people have acidic urine. This can be caused by a variety of factors, including being overweight and having type 2 diabetes. Uric acid, a waste product of chemical changes in the body, does not dissolve well in acidic urine; instead, it crystallizes and forms uric acid stones.

Uric acid stones can also form in people who don’t drink enough fluids (or lose too much fluid), eat high-protein diets, or have gout.

• Cystine stones (less than 1% of stones): These kidney stones form in people with a hereditary disorder called cystinuria. Cystinuria is a rare metabolic disorder that causes the kidneys to excrete an excess of the amino acid cystine into the urine. Having high amounts of cystine in the urine causes stones to form. Unlike most kidney stones, cystine stones often start to form in childhood.

Risk factors for kidney stones

Some lifestyle and health factors may increase your chances of developing one or more kidney stones. These risk factors^[9] include:

• Dehydration: Not drinking enough water can increase your risk of developing kidney stones. People who lose fluids quickly, live in warm climates, or sweat a lot may be at higher risk for dehydration than others.
• Genetics and personal history: You are more likely to develop kidney stones if someone in your family has had them. Furthermore, about half^[10] of people who have had kidney stones will have one or more again within 10–15 years if preventive measures are not taken.
• Obesity: A high body mass index (BMI), large waist size, and weight gain have been linked to an increased risk of developing kidney stones.
• Digestive diseases and surgery: Having gastric bypass surgery, inflammatory bowel disease (IBD), or chronic diarrhea can cause changes in the digestive process that affect your absorption of calcium and water. This increases the levels of stone-forming substances in your urine.
• Diet: Diets that are high in protein, sodium, and sugar can increase the risk of some forms of kidney stones. In particular, getting too much salt in your diet increases the amount of calcium your kidneys must filter, significantly increasing your risk for kidney stones.
• Biological sex and age: Kidney stones can affect men and women; however, men are at a higher risk for developing them than women. Kidney stones generally occur between the ages of 20 and 50^[11].
• Certain medical conditions: Some conditions that can increase your risk for kidney stones include renal tubular acidosis, cystinuria, hyperparathyroidism, and some UTIs.

Kidney stone symptoms

If your kidney stone is very small^[12] and moves easily through your urinary tract, you may not even know you have one. Some kidney stones may not cause symptoms until they pass from the kidney into the ureter (the tube connecting the kidney to the bladder). When this occurs, you may experience the following signs and symptoms^[13]:

• Sharp pain in the side and back below the ribs, sometimes coming and going in waves or fluctuating in intensity
• Pain that radiates (spreads outward) to the lower abdomen and groin
• Blood in the urine
• Persistent urge to urinate or urinating more frequently than usual
• Pain while urinating
• Urinating small amounts
• Nausea and vomiting
• Pink, red, or brown urine
• Cloudy or foul-smelling urine
• Fever and chills, if an infection is present

The pain caused by a kidney stone may move to a different location or increase in intensity as the stone moves through your urinary tract. If you experience any of the signs or symptoms of kidney stones, see your healthcare provider. He or she can provide proper diagnosis and treatment.

Kidney stone pain

The unfortunate truth is that kidney stones can be very painful. Some women have even described the pain associated with kidney stones as more excruciating than childbirth^[14]. Kidney stones can vary in size—many are as small as a grain of sand, while others can grow to be as big as a golf ball. Stones that are large or have jagged edges (like branched struvite stones) will likely be more painful than smaller, smoother ones. The pain associated with kidney stones begins when the stones move from the kidneys to the ureters. It is usually felt on either side of the lower back (depending on where the stone is located), and can come and go suddenly^[15]. If a kidney stone moves, pain may shift to the front of the body. Despite being painful, most kidney stones don’t require treatment when they’re small. Some home interventions that may help make the process of passing a kidney stone easier and less painful include drinking water and taking pain relievers. It is also recommended that you stay active, as moving around (rather than laying in bed) may help dislodge a kidney stone more quickly.

Kidney stone complications

In severe cases, kidney stones may cause health complications^[16], including:

• Recurring kidney stones
• Obstruction or blockage in the urinary tract
• Kidney failure
• Sepsis (a potentially life-threatening condition caused by the body’s response to an infection)—can occur after the treatment or removal of a large kidney stone
• Injury to the ureter during kidney stone removal surgery
• Urinary tract infection

If you have kidney stones, seeking treatment from your healthcare provider can help lower your risk of developing related complications.