What are kidney stones?

They are solid masses of crystals formed from substances, most of which are present in normal urine. Most stones consist of calcium, combined with either oxalate or phosphate (or both). Ten percent are formed of uric acid and often associated with gout.

People who suffer recurrent urinary infections may form very large stones, usually referred to as staghorns.

Most stones form in the kidney but a few develop in the bladder. They vary in size from a grain of sand to a golf ball.

How common are kidney stones?

Five to ten percent of the population develop stones. Kidney stones are more common in men, up to three times more common than women. Accurate figures are not available.

Why do stones form?

Normal urine contains substances that can inhibit crystal formation. Oversaturated (concentrated) urine has a high level of calcium, oxalate and uric acid. These encourage crystals to form and grow. This results from:

• increased amounts excreted by the kidneys
• low urine volume due to drinking too little fluid, especially in hot weather.

What symptoms do kidney stones cause?

• pain begins in the loin (near the spine at waist level) and extends to the groin. Initially the pain comes on in waves (colic), but may become constant. Sometimes the pain is abdominal or felt in the lower back. Pain is due to the stone obstructing urine flow through the ureter which joins the kidney to the bladder
• blood in urine. This must always be investigated
• repeated urinary infections
• passing a stone.

How can kidney stones be diagnosed?

X-Ray

Two types of x-rays may be done:

• abdominal region (similar to chest x-ray)
• intravenous urogram (IVU). Dye injected into an elbow vein is taken up and excreted by the kidneys.

X-rays show the whole urinary tract. Uric acid stones do not show unless they cause a blockage.

Ultrasound

Useful for showing the kidneys and stones within them; or whether they are blocked.

If you get an attack of kidney pain

Drink plenty! It helps to flush the stone through. If pain becomes worse call your doctor. Admission to hospital may be necessary. Stones 5 mm or less in diameter usually pass on their own.

What if the stone becomes stuck?

Surgical removal

This can be done in three ways:

• directly from the kidney or ureter
• through the bladder
• passing an instrument through, either removing the stone if small or shattering it with ultrasonic waves generated by a probe applied to the stone.

Lithotripsy

Externally generated sound waves are focussed on the stone. The shattered fragments are passed in the urine. Currently there is a lithotripter in Hamilton and a mobile unit which visits most hospitals. Not all stones require removal.

Should anything more be done?

Nearly all those who form one stone will produce another unless preventative measures are taken. The cause of stone formation should be investigated.

• take any stone you pass to your doctor for analysis
• blood and urine tests may be arranged by your doctor
• a dietician may be asked to evaluate your diet.

Stones may remain 'silent' for many years. In a number of instances no obvious cause can be found.

Can further stones be prevented?

Your chance of developing another stone is greatly reduced if you:

• drink plenty of fluid - at least two litres daily (water is readily available, no prescription needed, very cheap)
• take care not to eat too much calcium. You should eat no more than 300 ml of milk + 50 g of cheese + either an ice cream or ½ pottle of yoghurt every day
• watch your oxalate intake. You should eat no more than one serving of rhubarb + six slices of beetroot + two servings of either silverbeet, spinach or puha every day
• avoid excessive salt intake as it increases urine calcium excretion
• eat meat in moderation. Meat is the most important cause of increased calcium and uric acid excretion. Excessive intake (very common amongst men) should be avoided
• dietary assessment and modification must be done by a dietician. People must understand the reasons for the dietary advice and be encouraged to make a life long commitment
• drugs may be advised for specific conditions.

Long term follow-up should be arranged, especially if treatment has been advised and stones are still present. The correct treatment and the most appropriate follow-up for an individual person is best judged by a doctor specialising in the field.

Original material provided by the New Zealand Kidney Foundation. Reviewed by everybody.