The urinary tract is the system that produces urine and carries it out of your body. It is made up of the kidneys, the tubes that connect the kidneys to the bladder (the ureters), the bladder, and the tube that leads from the bladder out of the body (the urethra).

Sometimes, stones may form along the urinary tract and give rise to problems as a result of obstruction to urinary flow.  The most common type of stone contains calcium oxalate or calcium phosphate.  Less common types of stones include uric acid stone (associated with gout), and cystine stones.

What Causes Kidney Stones?

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Kidney stones form when there is a high concentration of certain chemicals in the urine (eg. calcium, phosphate, oxalate and uric acid) on one hand, and a low concentration of substances that prevent stone formation (the "inhibitors" such as citrate and magnesium) on the other.

Certain conditions affecting the urinary tract, such as urinary tract infections, cystic kidney diseases as well as certain metabolic diseases, are linked to stone formation.  Calcium oxalate stones are also more likely to develop in people with chronic inflammation of the bowel, or in those who have had intestinal bypass surgery.

Kidney stones may also be an inherited disease. If other people in your family have had kidney stones, you may have them too.

What Are The Symptoms?

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Most stones that remain in the kidneys do not cause any symptoms.  It is when the stone moves downward into the ureter, blocking the flow of urine, that the first symptoms suddenly appear:

• Sudden, severe pain that gets worse in waves.  The pain is typically felt in the lower back (in the loin region around the area of the kidneys) and may shift to the lower abdomen and groin.  People who have had a kidney stone often describe the pain as "the worst pain they have ever had."

• Often, there is associated nausea and vomiting.

• As the stone moves through the urinary tract, blood may appear in the urine (known as haematuria).

• As the stone moves down the ureter closer to the bladder, there may be the sensation of needing to urinate more frequently, and with greater urgency.  Some may also develop a burning sensation during urination (dysuria).  These symptoms of frequency, urgency and dysuria and known as the "lower urinary tract symptoms".  Lower urinary tract symptoms associated with a fever is more likely to be due to a urinary tract infection rather than stones.

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