What Are Kidney Stones?

Causes and Treatment of Renal Calculi

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Kidney stones, also known as renal calculi, are hardened deposits of minerals that form in the kidneys and can cause pain as they pass through the urinary tract. Kidney stones do not usually cause permanent damage if recognized early and treated appropriately.

Depending on the size of the stone, treatment may involve drinking a lot of water and letting the stone pass naturally or taking active measures to break up and remove the stone. Doctors refer to kidney stone disease as either nephrolithiasis or urolithiasis.

Close-up detail of a kidney stone (renal calculi)
Close-up detail of a kidney stone (renal calculi).

Javier Fernandez Sanchez / Getty Images

Kidney Stone Types

There is more than one type of kidney stone. The five types differ by their underlying cause, and some affect certain groups of people more than others:

  • Calcium oxalate: This is the most common type, caused by high concentrations of calcium (a mineral you absorb from food) or oxalate (a compound produced by the liver and found in certain foods) in urine. When this occurs, the compounds can bind together to form crystals.
  • Calcium phosphate: These stones are the result of a high urinary pH (meaning the urine is alkaline rather than acidic). This increases the concentration of calcium phosphate in the urine and promotes the formation of crystals. Stones like these are often due to metabolic disorders or medications that alter the urinary pH.
  • Cystine: These stones are due to a rare hereditary disorder called cystinuria that causes the overproduction of a compound called cystine. The overproduction can cause cystine to leak into the urine, causing recurrent stones.
  • Struvite: These stones are mainly associated with urinary tract infections (UTIs). Ammonia produced in response to UTIs can increase the urinary pH and cause the formation of struvite crystals composed of magnesium, ammonium, and phosphate.
  • Uric acid: This type of stone is caused by high levels of uric acid in the urine. Uric acid is a waste product that usually passes through the kidneys easily but can form crystals if concentrations are high.

Role of Urinary pH

Kidney stones are strongly influenced by urinary pH. Calcium phosphate and struvite stones are associated with a high urine pH (alkaline urine), while calcium oxalate, cystine, and uric acid stones are associated with a low urine pH (acidic urine).

Symptoms of Kidney Stones

Some kidney stones are as small as a grain of sand. Others can be as large as a pebble or even bigger. As a general rule, the larger the stone, the more noticeable the symptoms.

A kidney stone will not cause any symptoms until it begins to pass through the urinary tract. Pain is the central feature, which occurs as the stone moves through the kidney itself or through any part of the urinary tract, including the ureters, bladder, and urethra.

If the stone gets stuck in a ureter (the tube leading from the kidney to the bladder), it can block the flow of urine, causing the kidney to swell and the ureter to spasm. When this happens, symptoms typically include:

  • Severe, piercing pain in the side and back just below the ribs
  • Pain that radiates to the lower abdomen and groin
  • Pain or burning with urination

The pain generally comes in waves lasting 20 to 60 minutes and is caused by the contractions of the ureter as it tries to expel the stone. The pain, referred to as renal colic, can be extreme and be accompanied by symptoms such as:

  • Sweating
  • Restlessness
  • Nausea or vomiting
  • Hematuria (blood in urine)
  • Urinary urgency (a sudden and compelling urge to urinate)

Fever and chills, as well as cloudy, foul-smelling urine, may occur if there is an infection.

Calcium phosphate and struvite kidney stones caused by a high urinary pH tend to grow faster and can become quite large compared with those associated with a low urinary pH.


If treated appropriately and in a timely manner, most kidney stones will not cause any lasting injury. With that said, if a stone is large and not treated appropriately, a kidney stone can cause potentially severe complications, such as:

  • Severe scarring of the kidney, leading to permanent renal failure
  • Severe infections, including septicemia (blood poisoning)


Kidney stones are a common condition affecting one of every 11 people in the United States, most often those who are 30 years and over.

Dehydration is a major contributing factor to all types of kidney stones. Inadequate fluids increase the concentration of compounds in the urine, some of which can crystallize and form into hardened masses.

Diet can also play a part, including the high intake of animal proteins, sodium, and sugars. Some types are linked to underlying metabolic disorders (disruption of the processes your body uses to get energy from food) that directly or indirectly affect the kidneys.

Others are caused by genetic conditions passed from parent to child. Diabetes and obesity can also contribute.

With that said, kidney stones often have no single, definable cause. Multiple factors can contribute, some of which you can control and others of which you can't. This is best illustrated by the risk factors associated with each of the five types of kidney stones.

Calcium Oxalate Stones

Risk factors for calcium oxalate stones include:

Calcium Phosphate Stones

Risk factors for calcium phosphate stones include:

  • Dehydration
  • High sodium intake
  • Metabolic disorders like renal tubular acidosis (the kidneys are unable to remove enough acid or keep enough base)
  • Certain migraine or seizure medications like Topamax (topiramate)

Cystine Stones

Risk factors for cystine stones include:

  • Cystinuria
  • Dehydration
  • High sodium intake
  • A diet rich in animal proteins

Struvite Stones

Risk factors for struvite stones include:

Uric Acid Stones

Risk factors for uric acid stones include:

  • Dehydration
  • Obesity or type 2 diabetes
  • A purine-rich diet high in organ meats, alcohol, and certain fish or meats
  • Gout (a disorder in which crystals are deposited in a joint)
  • Chemotherapy
  • Taking certain medications, such as diuretics and immune suppressants


Key to the diagnosis of kidney stones is the early recognition of symptoms. This can sometimes be difficult because the symptoms are easily confused for other conditions like diverticulitis (inflammation of outpouchings of the colon) or a kidney infection, particularly in the early stages.

If a kidney stone is suspected, your doctor will start by reviewing your symptoms and medical history and gently palpating (touching and pressing) the affected area during the physical exam.

Other tests may be ordered based on the initial findings:

  • Blood tests: These include tests to check for abnormal calcium or uric acid levels as well as general markers for inflammation (such as C-reactive protein).
  • Urine tests: This includes a 24-hour urine collection to see if there are abnormally high mineral levels or abnormal urinary pH.
  • Imaging tests: High-speed or dual-energy computed tomography (CT) is preferred because it can detect small stones better than conventional X-rays.

Stone Analysis

Any passed stones will be sent to the lab for analysis. By determining the composition and cause of the stone, your doctor will be better able to prescribe preventive therapies and avoid repeat episodes.


The treatment of a kidney stone varies by its size and the underlying cause. Stones smaller than 5 millimeters (0.2 inches) will pass on their own in up to 98% of cases, while those that are 5 to 10 millimeters (0.2 to 0.4 inches) will pass spontaneously in around 50% of cases.

Smaller Stones

Doctors will often recommend time and patience with smaller stones, allowing them to pass on their own without the need for more invasive treatments. This often includes:

There are several home remedies that people claim can help pass stones faster and with less pain. This includes drinking diluted lemon juice or apple cider vinegar, the acids of which may help break up smaller stones.

Larger Stones

More aggressive treatments may be needed for larger kidney stones. This is especially true if they are causing bleeding, pose a risk of kidney damage, or are associated with a severe infection.

Based on the size, symptoms, and cause, your doctor may recommend:

  • Extracorporeal shock wave lithotripsy (ESWL): This is a technology that uses high-intensity sound waves to break the stones into tiny pieces. The procedure takes around 45 to 60 minutes and usually involves a sedative to minimize discomfort.
  • Ureteroscopy: This involves a narrow scope, called a ureteroscope, that is fed through the urethra and into the bladder and ureter. Performed under local or general anesthesia, the procedure can break up the stone and allow for the insertion of a stent (a small tube) to keep the ureter open and help it heal.
  • Percutaneous nephrolithotomy: This is a type of surgery performed under general anesthesia that uses specialized scopes and instruments to remove the stone through small incisions in your back.


People who have had or are at risk of kidney stones may reduce the risk by taking a few simple precautions. These include:

  • Drink water: A 2015 review in the journal Medicine found that people who produced 2 to 2.5 liters of urine daily were 50% less likely to develop kidney stones than those who produced less. Drinking 2 to 2.5 liters per day (8 to 10 cups) can usually accomplish this.
  • Avoid high-oxalate foods: If you are prone to kidney stones, avoid foods high in oxalates, such as spinach, chard, rhubarb, and star fruit, and limit potatoes, beets, bran, chocolate, and nuts. Also, take calcium with each meal.
  • Cut back on sodium: The Dietary Guidelines for Americans recommend a daily sodium intake of less than 2,300 milligrams per day. If you have a history of kidney stones, you may want to cut back even further, to 1,500 milligrams per day.
  • Eat less meat: Animal proteins boost uric acid levels; the culprits include not only meat but eggs and seafood as well. If you are at risk of hyperuricemia (high uric acid) due to kidney disease or other causes, limit your daily meat portion to the size of a deck of cards, or roughly 53 grams.
  • Drink lemon water: Citrate is a citric acid salt found in high concentration in lemons. There is evidence that drinking the diluted juice of two lemons (roughly 4 ounces) per day can reduce the risk of kidney stones, particularly in people at risk of calcium phosphate or struvite stones.


There is no minimizing the fact that kidney stones can be extremely painful and that minutes can seem like hours when you are trying to pass one. However, there are a number of things you can do to better cope until the stone finally passes:

  • Keep drinking fluids: Water is always the best choice, but if you're experiencing nausea, ginger ale or a lemon-lime soda can be soothing.
  • Avoid caffeine: The caffeine found in coffee, tea, and cola acts as a diuretic and can cause you to lose fluids quickly and become dehydrated.
  • Move around: Rather than curling up into a ball, walking and moving can help pass a stone more quickly. If you do decide to lie down, do so on your left side with your legs extended rather than pulled to the chest.
  • Treat the pain: When pain strikes, take two Tylenol every three hours.
  • Use heat therapy: Soaking in a hot tub or taking a hot shower can help relieve pain. Applying a heated pad to the area of pain may also help.

When to Seek Medical Care

Seek immediate care if the passing of a kidney stone is accompanied by:

  • HIgh fever with chills
  • Intolerable pain
  • Bloody urine
  • Cloudy, foul-smelling urine
  • Vomiting


A kidney stone is a hardened deposit of minerals that forms in the kidneys and causes pain as it passes through the urinary tract. There are several types of kidney stones, the causes of which include dehydration, medications, metabolic conditions, genetic disorders, digestive diseases, and diets rich in sodium, sugar, and animal proteins.

Kidney stones typically cause pain in the side and back, which can be excruciating and come in waves. Depending on the size of the stone, it may be treated conservatively (with pain killers, alpha-blockers, and plenty of water) or more aggressively (with surgery or shock wave therapy).

The risk of kidney stones can be reduced by drinking plenty of water and reducing your intake of sodium, animal proteins, and oxalate-rich foods like spinach, almonds, and potatoes.

A Word From Verywell

As common as kidney stones are, they can often be prevented by eating a healthy diet, keeping well hydrated, and staying fit. Even so, there are medical conditions that can place even the healthiest person at risk.

If you don't have any of the typical risk factors for kidney stones or have recurrent episodes, it is important to see a nephrologist (a specialist in kidney diseases) for a comprehensive evaluation. You may find that you have an undiagnosed condition like cystinuria or hyperparathyroidism that can either be managed or treated.

If you need help building the appropriate diet to manage or prevent kidney stones, ask your doctor for a referral to a registered dietitian with expertise in kidney health.

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By James Myhre & Dennis Sifris, MD
Dennis Sifris, MD, is an HIV specialist and Medical Director of LifeSense Disease Management. James Myhre is an American journalist and HIV educator.