Nephrolithiasis (kidney stones)
What is nephrolithiasis?
Kidney stones, or nephrolithiasis, is a common condition in which hard collections, or calculi, form in the renal system, usually in the tube between the kidney and the bladder. These collections are the result of urine becoming saturated with minerals such as calcium oxalate, calcium phosphate, struvite, uric acid or cystine.
Common types of stone are:[^2
- Calcium oxalate stones
- Calcium phosphate stones
- Uric acid stones
- Struvite stones
- Cystine stones
Around 80 percent of all kidney stones, also called calculi, are calcium stones.
These stones can vary in size - from a few millimeters to a large staghorn shape a few centimeters in length. Kidney calculi are more common in men than in women, and tend to occur in adults between the ages of 20 and 50. People between the ages of 35 and 45 are the most likely to be affected, but the disease can affect people of any age. It is rare to develop a stone for the first time over the age of 50. Over half a million people in the US are affected by kidney stones every year. Kidney stones are more common in whites and Asians than in people with African, Native American or African-American heritage.
Symptoms occur when a stone leaves the kidney and enters the tighter ureter, the tube between the kidney and bladder, on its way to the bladder. A stone that is moving is much more painful than a stone that has not moved from its original place.
Typical symptoms are severe pain in the back and belly, difficulty urinating and red or brown urine. Common treatment methods include good hydration, pain relief and anti-emetics. About 20% of patients require procedures such as lithotripsy, breaking up the calculus with shock waves, to remove the stones, when kidney stones have caused pain, infection or obstruction. Most people recover fully, without any complications.
Risk factors and causes of nephrolithiasis
Kidney stones are more common in men, and in adults between 20 and 50 years of age, but very rare in children.It is most common in adults who have a low fluid intake and consequently produce little urine, which can contain high amounts of stone-forming substances.
Kidney stones are also more common in people who have gout (in the case of uric acid stones), or who have a family member who also suffers from kidney stones. The genes that can increase a person’s chance of developing nephrolithiasis have been identified.
Infections of the urinary tract may lead to kidney stones. Other general risk factors are dehydration and being overweight or obese.
- Anatomical abnormalities such as horseshoe kidney or ureteral stricture
- Hyperparathyroidism, i.e. an overactive parathyroid gland
- Metabolic disorders, such as hypercalciuria, hyperuricosuria or chronic metabolic acidosis
- Intestinal problems such as Crohn’s Disease
- Weight-loss surgery
- Living in a hot climate and its risk of dehydration
- Too much exercise and its risk of dehydration
- Too little exercise and its risk of obesity
- A diet high in protein, salt or sugar, especially fructose and sucrose
Some medications can increase the risk of forming renal calculi. These include:
- Indinavir, an antiretroviral medication
- Atazanavir, an antiretroviral medication
- Guaifenesin, an expectorant medication
- Triamterene, a medication used for the treatment of hypertension and edema
- Silicate, which is used in antacids
- Sulfasalazine, a medication used for the treatment of rheumatoid arthritis, colitis and Crohn's disease
- Sulfadiazine, a drug used for the treatment of otitis media ear infections
- Ceftriaxone, a drug used for the treatment of bacterial infections
Stones caused by struvite, as opposed to calcium, are caused by urea-splitting bacteria such as Klebsiella, Pseudomonas and Proteus species, and indicate an underlying urinary tract infection. Struvite stones are more common in women than in men, and are responsible for between 1 and 5 percent percent of kidney stones.[^a] They will reoccur if the underlying UTI is not treated.
Kidney stones caused by uric acid are associated with acidic urine, usually with a pH of below 5.5. These account for only around 10% percent of calculi and are often associated with gout. Chemotherapy for conditions such as leukemia and lymphoma may also cause high urine pH. It is generally thought that certain foods can increase risk of developing uric acid stones. These include animal protein from meats or fish. Excessive salt and excessive sucrose and fructose intake are also known to increase the risk of stones forming, and should be avoided.
People who have had calcium oxalate stones in the past or who have a high rate of oxalate excretion should reduce consumption of:[^10]
- Vitamin C
High intake of purine in the diet causes the body to produce large amounts of monosodium urate. The risk of developing uric acid stones is hereditary.
People with uric acid stone disease or hyperuricosuric calcium oxalate stones should reduce consumption of:[^10]
- Calf thymus
- Poultry skin
- Herrings with skin
Cystine stones are rare and may be caused by genetic factors that cause the body to reabsorb cystine, ornithine, lysine and arginine from the kidneys. In cases where cystine stones develop, the urine is supersaturated with cystine, which causes crystals to be deposited and stones to form.
Symptoms of nephrolithiasis
Typical symptoms are severe pain at the back and flank, difficulty urinating and passing only small amounts of urine at a time. The pain is often cramping or like a spasm and tends to come in waves. Some people might also have nausea, vomiting and may pass red or brown urine. Symptoms occur when a stone leaves the kidney and enters the tighter ureter, the tube between the kidney and bladder.
Pain is one of the most obvious symptoms of kidney stone obstructions. Where the pain is felt, and where it radiates to in the body, can indicate where the calculus is within the renal system. The pain that accompanies a kidney stone is felt acutely in the flank (the side) and radiates down the groin on the same side. Not all stones cause pain that spreads. Some stones may cause no pain at all.
Pain is caused not by the kidney stone itself, but by muscle spasms, inflammation and irritation at and around the site of the obstruction. Factors that influence how painful the kidney stone is, include:
- Whether the stone is moving
- Whether it is twisted or tilted in the ureter or urethra
- Whether the obstruction is complete or partial
- Where it is in the renal system
- How big the stone is
Good to know: Pain from kidney stones is often described as excruciating and intermittent, and often occurs in cycles that last between 20 minutes and an hour. People with painful kidney stones often cannot keep still because of the pain. They are often ashen, pale and sweaty, with a tender abdomen.
- Nausea and vomiting, which diminish as pain is relieved
- Fever and chills
- Blood in the urine, known as hematuria
- Cloudy or bad-smelling urine
- Tender abdomen
- Lack of urine
- Urinary retention
- Gravel or stones in the urine
Diagnosis of nephrolithiasis
Diagnosis of kidney stones is often based on the typical symptoms and physical examination. A urine dipstick test may show blood and pus in the urine, and help confirm the presence of a kidney stone.
A person being examined for kidney stones will be asked about their medical history and will be physically examined. They will also be given a computed tomography (CT) scan. X-rays and ultrasound tests can determine the presence of stones, but CT scans are preferred during the diagnostic process, because they can determine the size and location of the stone. MRI scans are not generally helpful. In pregnant women; a renal ultrasound is usually ordered. Renal ultrasound is also often used to diagnose kidney stones in children, although in some cases a CT scan may also be needed.
- 24-hour urine collection test, once the patient is free of stones, to measure changes in the values for urinary electrolytes, reduced urine volume and to determine the underlying metabolic cause for nephrolithiasis
- Blood tests, if the person is feverish
The calculus/kidney stone will be analysed after it has been passed in the urine or extracted during surgery.
People with the following conditions may need further tests, as determined by their physicians:
- Bone metastases
- Solitary kidney
- Urinary tract anomalies
Treatment of nephrolithiasis
The treatment varies, depending on the size of the kidney stone and the severity of the symptoms. Small stones usually pass with no need for medical assistance. Drinking plenty of water may help to flush the stone from the urinary system.
Pain medication is often needed while passing a renal calculus. In severe cases, opiates may be prescribed. However, in most cases, acetaminophen/paracetamol is usually sufficient. 80 percent of stones pass without serious medical intervention and needing no inpatient treatment. About 20 percent lead to situations that require hospitalization.
People may need to be admitted to hospital if the following factors are present:
- Anuria, when the kidneys do not produce urine
- Persistent or severe pain
- Inadequate fluid intake as a result of nausea or vomiting, resulting in dehydration
- Poor social support
- Inability to access follow-up outpatient care
- Being older than 60 years of age
Good to know: If a fever is present, infection may also be present. Because infection can be very serious, the affected person should receive medical treatment as soon as possible.
Treatment at home may be possible for most people, because most stones smaller than 5mm pass on their own and do not cause infection or need surgical help to pass. People may be cared for at home if:
- Their pain has been relieved and can be managed with acetaminophen/paracetamol
- They can drink fluids
- They have good social support
- They have no complications, such as fever or urinary blockage
Painkillers, antiemetics and antidiuretics are commonly used in both inpatient and outpatient treatment of kidney stones. Painkillers, such as morphine may be used to control severe pain; moderate or mild pain can be controlled with acetaminophen or codeine. Antibiotics are only used in cases where an infection has developed.
Other medications used to treat uric acid kidney calculi are:
- Uricosuric agents, which increase the amount of uric acid excreted
- Alkalinizing agents, such as sodium bicarbonate and potassium citrate
Big stones, with a diameter of more than 10mm and which are lodged in the ureter, might need assistance to pass, especially if they are blocking the passage of urine. Stones with a diameter of less than 10mm that are in the distal ureter and do not have complications such as infection, should be removed if they have not passed on their own within four to six weeks. This can involve lithotripsy (breaking up the stone with shock waves), or the surgical removal of stones, or the removal of the stone with an endoscope, a small tube with a camera and surgical tools.
Shockwave lithotripsy (ESWL) is a non-invasive procedure where sound waves are used to break the stones into fragments small enough to pass through the ureter and out of the body through the urethra. If lithotripsy is not used, other endoscopic methods are possible, such as uteroscopic lithotripsy (URS) or percutaneous nephrostomy.
In uteroscopic lithotripsy, an endoscope is introduced to the urethra and moves through the bladder into the ureter to the stone’s location. The stone is then removed. In cases where access to the urethra is complicated because of an enlarged prostate, the endoscope will be introduced via a small incision in the bladder.
In a percutaneous nephrostomy, an endoscope is introduced via a small incision in the skin of the flank, directly into the kidney.
Some very large or complicated stones may need open surgery.
Struvite stones must be removed, as they are infectious or infected foreign bodies. The stones will reoccur if the urinary tract infection that underlies their formation is not resolved.
Prevention of nephrolithiasis
Preventing kidney stones from forming involves dietary changes and correct hydration. In all cases, it is important to remain well hydrated, consuming about 2.5 quarts of water each day. It is also important to limit sugar and salt in the diet and to eat a diet high in fruit and vegetables. In cases where the person is overweight, they should lose the excess weight.
Good to know: High-animal protein diets and crash diets should be avoided, as they can unbalance the pH and chemical makeup of urine. For more information, see the section of prevention of kidney stones, above.
People who are concerned about the role their diets may play in the formation of kidney stones, should consult their physicians, specialist nephrologists and/or a dietitian.
Good to know: Low-calcium diets are not indicated for the prevention of calcium oxalate stones, as low calcium diets cause oxalate reabsorption to increase.
In cases of uric acid stones, allopurinol will be prescribed to prevent high levels of uric acid building up in the blood. Alkalinizing agents may also be prescribed to make urine more alkaline.
FAQs for nephrolithiasis
Q: Do kidney stones recur once they have been treated?
A: Yes. People who have had a kidney stone, have a 50 percent chance of developing another stone within five to seven years. Maintaining high fluid intake, as well as making dietary changes and maintaining a healthy weight, can help postpone the recurrence of stones.
Q: Can kidney stones cause long-term kidney damage?
A: Yes. Complications can occur, in some cases within hours, that can be serious in themselves. These include sepsis and high fever. Struvite stones, as noted above, are the result of an underlying UTI, which could potentially cause long-term damage if left untreated. In some cases, pyelonephritis may result if kidney stone obstructions are left untreated, and renal damage may be permanent.
Q: What are the complications of kidney stones?
A: Complications include:
- Recurrent UTIs
- Acute kidney injury
- Glomerular damage
- Chronic kidney disease
Q: What is the difference between kidney stones and bladder stones?
A: Kidney stones develop in the kidneys and move into the ureter, bladder and urethra. Bladder stones develop in the bladder. Bladder stones make up about 5 percent of all calculi found in the renal system. They are usually the result of foreign bodies, infection and obstruction, and the most common cause of bladder stones is urinary stasis. The majority of bladder stones occur in men who have bladder outflow problems, which cause urine to remain in the bladder after urination.
Q: What are some common foods that contain high levels of oxalate and may therefore need to be eaten only in very low amounts or not at all?
A: It is best to speak to a physician or dietitian before adding or eliminating foods. Not every case of kidney stones has the same cause, and therefore some of the foods listed below may not be relevant to the disease. Furthermore, this list is not exhaustive.
Some fruits, vegetable and processed foods are high in oxalate. These include rhubarb, spinach, beetroot, avocado, oranges, raspberries, dates, grapefruit and kiwi fruit. Nuts and nut butter may also be best avoided by some people. Bran flakes and potato chips may also be problematic.
Other names for nephrolithiasis
- Ureteral stone
- Kidney stones