Nephrolithiasis

Kidney stones, Renal calculi, Urolithiasis

Kidney stones are hard masses made of crystals that form inside the kidneys and can cause severe pain as they move through the urinary tract. While small stones may pass on their own, larger ones may require medical procedures to break them up or remove them.

Table of contents

• What is Nephrolithiasis?
• How Common Are Kidney Stones?
• Symptoms
• Causes and Risk Factors
• Types of Kidney Stones
• Diagnosis
• Treatment
• Prevention

What is Nephrolithiasis?

Nephrolithiasis specifically refers to calculi, or stones, in the kidneys. These are hard objects made of minerals and salts that form inside the kidneys from substances found in urine^[1]. The stones can be as small as a grain of sand or, rarely, larger than a golf ball^[3].

Kidney stones can affect any of the organs that make urine or remove it from the body, from the kidneys to the bladder^[1]. When stones form in the kidneys, they may stay there or move down through the ureter (the tube that connects the kidney to the bladder). Ureteral calculi almost always originate in the kidneys, although they may continue to grow once they lodge in the ureter^[4].

Depending on the size of your kidney stone, you may not even realize that you have one. Smaller stones can pass through your urinary tract in your urine with no symptoms^[3]. Large kidney stones can get trapped in your ureter, causing urine to back up and limiting your kidney’s ability to filter waste from your body. It can also cause bleeding^[3].

How Common Are Kidney Stones?

Kidney stones are a common disorder, with an annual incidence of eight cases per 1,000 adults^[7]. They occur in 1 in 11 people at some time in their lifetimes^[2]. About 1 in 10 people will get a kidney stone during their lifetime^[3].

The prevalence of nephrolithiasis is increasing in the United States, from one in 20 adults in 1994 to one in 11 adults in 2010^[7]. Incidence and prevalence rates have been increasing over the last several decades^[4].

Men are affected twice as much as women^[2]. Kidney stones are most common in men in their 30s and 40s, and they’re also more common among non-Hispanic white people^[3]. The annual incidence peaks around midlife in developed countries^[7].

Symptoms

The most common symptom of kidney stones is pain in your lower back, belly, or side, which is also called flank pain^[3]. It might feel like it extends from your groin to your side. It can be a dull pain or sharp and severe. It’s sometimes called colicky pain because it can get worse in waves^[3].

Acute renal colic presents as cramping and intermittent abdominal and flank pain as kidney stones travel down the ureter from the kidney to the bladder^[7]. This is probably the most excruciatingly painful event a person can endure. The pain is often described as being worse than childbirth, broken bones, gunshot wounds, burns, or surgery^[4].

Other kidney stone symptoms include^[3]:

• Nausea and vomiting
• Bloody urine
• Pain when you urinate
• Inability to urinate
• Feeling the urge to urinate a lot
• Fever or chills
• Cloudy or foul-smelling urine

Smaller kidney stones may not cause pain or other symptoms^[3]. Pain is often accompanied by nausea, vomiting, and malaise; fever and chills may also be present^[7].

The pain generated by renal colic is primarily caused by dilation, stretching, and spasm because of the acute ureteral obstruction^[4].

Causes and Risk Factors

Kidney stones form when solutes crystallize out of urine to form stones^[2]. Your urine contains minerals, acids, and other substances, like calcium, sodium, oxalate, and uric acid. When you have too many particles of these substances in your urine and too little liquid, they can start to stick together, forming crystals or stones. Kidney stones can form over months or years^[3].

Often, stones form when the urine has less water in it. This lets minerals form crystals and stick together^[1]. Development of the stones is related to decreased urine volume or increased excretion of stone-forming components such as calcium, oxalate, uric acid, cystine, xanthine, and phosphate^[2]. Stones may also be caused by low urinary citrate levels, which are inhibitors of stone formation, or excessive urinary acidity^[2].

Urolithiasis may occur due to anatomic features leading to urinary stasis, low urine volume, dietary factors (such as high oxalate or high sodium), urinary tract infections, systemic acidosis, medications, or, rarely, inheritable genetic factors such as cystinuria^[2].

Most are of noninfectious etiology and are associated with low fluid intake, hot climate, and certain comorbidities and risk factors such as hypertension, gout, obesity, nonalcoholic fatty liver disease, and excessive intake of protein, carbohydrates, and sodium^[7]. Increasing exposure to these risk factors may explain the rising incidence of kidney stones and their prevalence in men, non-Hispanic whites, and persons with low socioeconomic status^[7].

You might be at a higher risk of developing kidney stones if you^[3]:

• Don’t drink enough fluids
• Eat meat and other protein-rich foods
• Eat foods high in sodium or sugars (sucrose and fructose)
• Take vitamin C supplements
• Have a family history of kidney stones
• Have a blockage in your urinary tract
• Have had stomach or intestine surgery, including gastric bypass surgery
• Take certain medications

Genetic, metabolic, and environmental factors can contribute to stone formation^[4].

Types of Kidney Stones

Stones are named for the type of crystals they’re made up of^[3].

Calcium stones: Most patients with nephrolithiasis (75 to 85 percent) form calcium stones, most composed primarily of calcium oxalate^[2]. Calcium-based stones can form when you eat high-oxalate or low-calcium foods and aren’t drinking enough fluids. Calcium oxalate stones are the most common type of kidney stones^[3]. Stones may also be made of calcium phosphate, or both calcium oxalate and calcium phosphate^[7].

Uric acid stones: Eating animal proteins (beef, poultry, pork, eggs, and fish) can cause uric acid stones to form^[3]. Uric acid stones may form when your urine contains too much acid^[2].

Struvite stones: Bacterial infections can cause struvite stones^[3]. A struvite stone may form after an infection in your urinary system^[2]. Repeated infections can lead to a staghorn calculus, a very large kidney stone that usually needs to be surgically removed^[3].

Cystine stones: An inherited condition called cystinuria causes cystine stones^[3]. Cystine is a substance made of two cysteine amino acids bound together^[3]. Cystine stones are rare^[2], and cystinuria, the disease that causes cystine stones, runs in families^[2].

Diagnosis

Diagnosis involves the steps that your healthcare professional takes to find out if you have kidney stones. Diagnosis also can include testing to find the cause and chemical makeup of kidney stones. Your healthcare professional starts by giving you a physical exam^[8].

You also may need tests such as^[8]:

Blood tests: Blood tests may reveal too much calcium or uric acid in your blood. Blood test results help track the health of your kidneys. These results also may lead your healthcare professional to check for other health conditions^[8].

Urine testing: Your healthcare professional may ask you to collect samples of your urine over 24 hours. The 24-hour urine collection test may show that your body is releasing too many stone-forming minerals or too few substances that prevent stones^[8].

Imaging: Imaging tests such as CT scans may show kidney stones in your urinary tract. An advanced scan known as a high-speed or dual energy CT scan may help find tiny uric acid stones. Simple X-rays of the abdomen are used less often. That’s because this kind of imaging test can miss small kidney stones. Ultrasound is another imaging option to diagnose kidney stones^[8].

The diagnostic workup consists of urinalysis, urine culture, and imaging to confirm the diagnosis and assess for conditions requiring active stone removal, such as urinary infection or a stone larger than 10 millimeters^[7].

Analysis of passed stones: You may be asked to urinate through a strainer to catch any stones that you pass. Then a lab checks the chemical makeup of your kidney stones. Your healthcare professional uses this information to find out what’s causing your kidney stones and to form a plan to prevent more kidney stones^[8].

Treatment

Health care professionals usually treat kidney stones based on their size, location, and what type they are^[10].

Treatment for Small Stones

Small kidney stones may pass through your urinary tract without treatment. If you’re able to pass a kidney stone, a health care professional may ask you to catch the kidney stone in a special container^[10]. A health care professional may advise you to drink plenty of liquids if you are able to help move a kidney stone along. The health care professional also may prescribe pain medicine^[10].

It can take as long as three weeks for kidney stones to pass on their own^[3]. The size of the stone is an important predictor of spontaneous passage. A stone less than 4 millimeters in diameter has an 80 percent chance of spontaneous passage; this falls to 20 percent for stones larger than 8 millimeters in diameter^[9].

Conservative management consists of pain control, medical expulsive therapy with an alpha blocker, and follow-up imaging within 14 days to monitor stone position and assess for hydronephrosis (swelling of the kidney)^[7]. Nonsteroidal anti-inflammatory drugs are the first choice for pain relief in patients with kidney stones^[7]. Alpha blockers are the first choice for medical expulsive therapy in patients with kidney stones^[7].

Treatment for Larger Stones

Larger kidney stones or kidney stones that block your urinary tract or cause great pain may need urgent treatment. If you are vomiting and dehydrated, you may need to go to the hospital and get fluids through an IV^[10].

A urologist can remove the kidney stone or break it into small pieces with the following treatments^[10]:

Shock wave lithotripsy: The doctor can use shock wave lithotripsy to blast the kidney stone into small pieces. The smaller pieces of the kidney stone then pass through your urinary tract. A doctor can give you anesthesia during this outpatient procedure^[10]. Shock wave lithotripsy involves using ultrasound (high-frequency sound waves) to pinpoint where a kidney stone is. Ultrasound shock waves are then sent to the stone from a machine to break it into smaller pieces so it can be passed in your urine^[14].

Ureteroscopy: During ureteroscopy, the doctor uses a ureteroscope, which is longer and thinner than a cystoscope, to see detailed images of the lining of the ureters and kidneys. The doctor inserts the ureteroscope through the urethra to see the rest of the urinary tract. Once the stone is found, the doctor can remove it or break it into smaller pieces. The doctor performs these procedures in the hospital with anesthesia. You can typically go home the same day^[10].

Percutaneous nephrolithotomy: The doctor uses a thin viewing tool, called a nephroscope, to locate and remove the kidney stone. The doctor inserts the tool directly into your kidney through a small cut made in your back. For larger kidney stones, the doctor also may use a laser to break the kidney stones into smaller pieces. The doctor performs percutaneous nephrolithotomy in a hospital with anesthesia. You may have to stay in the hospital for several days after the procedure^[10].

After these procedures, sometimes the urologist may leave a thin flexible tube, called a ureteral stent, in your urinary tract to help urine flow or a stone to pass^[10].

Prevention

The best way to prevent kidney stones is to make sure you drink plenty of water each day to avoid becoming dehydrated^[21]. To prevent stones returning, you should aim to drink up to 3 litres (5.2 pints) of fluid throughout the day, every day^[21].

Staying hydrated dilutes the urine, so crystals can’t clump together and become stones. A meta-analysis from the National Kidney Foundation found that people who produced 2 to 2.5 liters of urine daily were 50 percent less likely to develop kidney stones than those who produced less. It takes about 8 to 10 eight-ounce glasses (about 2 liters total) of water daily to produce that amount^[18].

You’re advised to^[21]:

• Drink water, but drinks like tea and coffee also count
• Add fresh lemon juice to your water
• Avoid fizzy drinks
• Not eat too much salt

Keeping your urine clear helps to stop waste products getting too concentrated and forming stones. You can tell how diluted your urine is by looking at its color. The darker your urine is, the more concentrated it is. Your urine is usually a dark yellow color in the morning because it contains a build-up of waste products that your body’s produced overnight^[21].

Citrate, found in citrus fruits like lemons, has been shown to inhibit the formation of kidney stones. Enjoying a glass of fresh lemonade or adding lemon to your water not only provides a refreshing flavor but also promotes urinary citrate, reducing the risk of stone formation^[18].

All patients with kidney stones should be screened for risk of stone recurrence with medical history, basic laboratory evaluation, and imaging. Lifestyle modifications such as increased fluid intake should be recommended for all patients, and thiazide diuretics, allopurinol, or citrates should be prescribed for patients with recurrent calcium stones^[7].

Dietary Changes

Depending on the type of stones you have, your doctor may advise you to cut down on certain types of food^[21].

Control sodium intake: High sodium levels in the diet can lead to increased calcium excretion in the urine, contributing to stone formation. Be mindful of your sodium intake by avoiding processed foods and opting for fresh, whole foods prepared with minimal salt^[18]. A high-sodium diet increases the amount of calcium in your urine. This can trigger kidney stones in people who are already susceptible to them^[24].

Eat calcium-rich foods: While calcium is essential for bone health, it’s important to get calcium from food sources like dairy products and leafy greens^[18]. Good sources include yogurt, soy products, beans, lentils, and seeds. Dietary calcium binds oxalate in the intestines, so less gets absorbed and lower concentrations end up in urine^[18].

Moderate oxalate consumption: Some kidney stones are made of calcium oxalate, so it’s wise to moderate your intake of high-oxalate foods like spinach, beets, nuts, and chocolate. Cooking or steaming these foods can reduce their oxalate content, making them safer for consumption^[18].

Choose the right proteins: Animal proteins, such as red meat, can increase the risk of certain types of kidney stones. Consider incorporating plant-based proteins like legumes, tofu, and nuts into your diet^[18].

Maintain a healthy weight: Obesity is a significant risk factor for kidney stones. Adopting a balanced diet and engaging in regular physical activity can help you achieve and maintain a healthy weight, reducing the likelihood of stone formation^[18].

Patients should increase daily fluid intake to 2.5 to 3 liters per day to prevent recurrence of kidney stones^[7]. Thiazide diuretics, potassium citrate, or allopurinol should be prescribed after recurrence of calcium stones, even in the absence of metabolic abnormalities^[7].

In general, the treatment of stone disease reduces its recurrence rate, but only seldom results in stable remission^[15].