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Kidney Stones

Kidney Stones: What is it, Causes, Risk Factors, Symptoms, Diagnosis, Prevention, and More | Singapore General Hospital

Kidney Stones - What it is

The kidneys are two beanshaped organs located below your chest, one on each side of the spine. The kidneys remove extra water and wastes from the blood, producing urine. They also produce hormones and keep a stable balance of salts in the blood. Narrow tubes called ureters carry urine from the kidneys to the bladder, an oval-shaped reservoir for urine in the abdomen.

A kidney stone is composed of crystals formed by chemicals that separate from the urine that builds up in the kidney.

The most common type of stone contains calcium oxalate or calcium phosphate. A less common type of stone, caused by infection in the urinary tract, is called a struvite stone. Other rarer stones include uric acid stones and cystine stones.

Kidney Stones - Symptoms

Many people may not feel any symptoms. The first symptom of a kidney stone is severe pain, which begins suddenly when a stone moves in the urinary tract and blocks the flow of urine.

Typically, you will feel a sharp, cramping pain in your back and side, and around the area of the kidney. The pain may shift to the lower abdomen later on. Sometimes, you may also experience nausea and vomiting.

As the stone moves and the body tries to push it out, blood may appear in your urine making the urine pink. As the stone moves down the ureter closer to the bladder, you may feel the need to urinate more often or a burning sensation during urination. If fever and chills accompany any of these symptoms, an infection may be present.

Kidney Stones - How to prevent?

You are likely to form another if you have had more than one kidney stone. Therefore, prevention is important.

Adequate water intake. If you tend to form stones, try to drink enough liquid throughout the day to produce at least two litres of clear urine.

Calcium intake. In the past, people who form calcium stones were told to avoid dairy products and other foods with high calcium content. Recent studies have shown that foods high in calcium, including dairy products, may help prevent calcium stones. Older women taking calcium supplements to prevent bone loss should continue to do so.

Oxalate intake. If you are prone to forming calcium oxalate stones you may be asked by your doctor to limit or avoid certain foods if your urine contains an excess of oxalate. Foods that have medium amounts of oxalate may be eaten in limited amounts.

Vitamin D intake. You may be told to avoid food with added vitamin D and certain types of antacids that have a calcium base.

Meat intake. If you have highly acidic urine you may need to eat less meat, fish, and poultry as these foods increase the amount of acid in the urine.

High-oxalate Foods

  • Spinach, rhubarb, beets
  • Peanuts
  • Soybean crackers
  • Chocolate
  • Black tea
  • Sweet potatoes

Medium-oxalate Foods

  • Grapes
  • Celery, green pepper
  • Raspberries, strawberries
  • Marmalade
  • Liver

Kidney Stones - Causes and Risk Factors

Causes of kidney stones

Stones form as a result of urine with a high concentration of certain chemicals (such as calcium, oxalate, phosphate, uric acid and others) and a low concentration of substances that stop stone formation (urinary inhibitors such as citrate and magnesium).

Urinary tract infections, kidney disorders such as cystic kidney diseases, and certain metabolic disorders are linked to stone formation.

Calcium oxalate stones may also form in people with chronic inflammation of the bowel or have had an intestinal bypass operation, or ostomy surgery.

Risk factors of kidney stones

Stones occur more frequently in men, and most commonly between 40 and 70 years old. Once you get more than one stone, other stones are likely to develop.

Kidney Stones - Diagnosis

This requires imaging of the urinary tract, which includes:

  • X-ray or ultrasound of the kidneys and bladder, or
  • Intravenous urogram (IVU) or computerised tomography (CT) scan

Additional urine and blood tests may be needed to exclude infection and impairment of kidney function.

You may be asked to collect urine for 24 hours to measure urine volume and the levels of chemicals in the urine. Your doctor will also ask about your medical history, occupation, and eating habits.

Kidney Stones - Treatments

Most small kidney stones can pass through the urinary system with plenty of water - six to eight glasses a day - to help move the stone along. For larger stones, the following treatment options are available :

Medical Therapy

Certain medications may help prevent calcium and uric acid stones by controlling the amount of acid or alkali in the urine which are key factors in crystal formation. The medicine allopurinol may also be useful in some cases of hyperuricosuria where the chemical uric acid is secreted in large amounts in the urine.

Surgical Treatment

There are three ways to treat stones using surgery. This includes :

Extracorporeal shock wave lithotripsy (ESWL): You lie on a special machine that produces shock waves. The shock waves are created outside the body and travel through the skin and body tissues until they hit the denser stones. The stones break down into small particles that pass easily through the urinary tract in the urine. ESWL is usually done on an outpatient basis. Recovery time is relatively short, and most people can resume normal activities in a few days. Many people have blood in their urine for a few days after treatment.

Complications may occur with ESWL. Bruising and minor discomfort in the back or abdomen from the shock waves can occur. To reduce the risk of complications, patients are normally told to avoid aspirin and other medicines that affect blood clotting for several weeks before treatment. Sometimes, the shattered stone particles cause a minor blockage of the urinary tract which requires the placement of a stent into the ureter to help the fragments pass. If the stone is not completely shattered with one treatment, additional treatments may be needed.


Percutaneous nephrolithotomy (PCNL): PCNL is often used when the stone is quite large or in a location that does not allow for the eff ective use of ESWL.

In this procedure, the surgeon makes a tiny incision in the back and creates a tunnel directly into the kidney. The surgeon uses a nephroscope to locate and remove the stone. A small tube called a nephrostomy tube is left in the kidney for a few days.

The advantage of percutaneous nephrolithotomy is that some of the stone fragments can be removed directly instead of relying solely on their natural passage from the kidney.

Ureteroscopic stone removal: Ureteroscopy may be needed for mid- and lower-ureter stones. The surgeon passes a ureteroscope, a small fi beroptic instrument, through the urethra and bladder into the ureter to locate and fragment the stone with laser energy and remove it with a cage-like basket. A small stent may be left in the ureter for a few weeks to help urine flow.


Kidney Stones - Preparing for surgery

Kidney Stones - Post-surgery care

Kidney Stones - Other Information

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