About Kidney Stones

What is a kidney stone?

A kidney stone is hard piece of material like any other stone. It may form in the kidney and either grow steadily larger in size or migrate down the urinary system. A stone may pass through the urinary system without problems, but larger stones may get stuck and cause pain.

Most stones contain calcium, but also can contain other materials known as uric acid, struvite, or cystine

Is there a reason or a predisposing factor for getting a kidney stone?

Several factors make the development of a stone more likely. These include:

  • previous history of kidney stones: The risk after one year is about 15%, 35% at 5 years at 55% at 10 years.
  • other family members who have had stones
  • diet: certain dietary factors increase or reduce the risk of stones
  • medical conditions: previous bowel surgery, urinary infections, hyperparathyroidism, gout, cystinuria
  • excess vitamins: more than 2 g of vitamin C can increase the risk of stones
  • diarrhoea
  • dehydration
  • Poor mobility (e.g. confined to a bed or restricted mobility because of a broken limb)

How common are stones?

About 10% or 1 in 10 men will have stone in their lifetime. Women are affected less frequently (i.e. 5% or 1 in 20 women). Kidney stones are more common in Caucasians and occur more frequently between the ages of 20 and 40 years.

What are the symptoms of a kidney stone?

The symptoms depend of the size of the stone, position in the urinary system and whether the stone is moving or not. The pain is called 'renal colic'.

Pain (renal colic): this is usually felt in the back and spreads through to the front. Usually, the pain comes in waves, and it's difficult to get into a comfortable position. The pain lasts for between 20 and 60 minutes, and is very severe. The pain is worse as the stone moves and is sometimes associated with an urgent desire to pass urine towards the end of its journey.

Blood in the urine: Usually, there is blood detected in the urine by chemical analysis ('Haematuria') when a stone is present. However, it is not usually possible to see the blood with the naked eye.

Passing gravel or stones in the urine: very small stones may be seen in the urine as they are passed.

Other symptoms: There may be nausea, vomiting, and an urgent desire to pass urine. Sometimes, an infection may develop giving rise to a fever, shaking and shivering (rigors). This needs emergency treatment in a hospital.

Recurrent urine infections: recurrent urine infections can sometimes be caused by urinary stones.

What happens when a stone blocks a kidney?

If the stone prevents the passage of urine from the kidney to bladder, pressure builds up behind the kidney. The function of the kidneys starts to suffer over a period of weeks. The obstruction can also cause stagnation of the urine, which can lead to infection and further damage to the kidneys. It is, therefore, important to relieve or prevent obstruction of the kidneys.

If a stone is in a ureter for a prolonged period, sometimes the ureter can be irritated so severely resulting in a narrow area ('stricture') further preventing the passage of urine.

Providing a stone passes within a few weeks and no infection occurs in an otherwise healthy individual, there is rarely long term damage.

How are kidney stones diagnosed?

A diagnosis of a stone is based on the history of the clinical symptoms, what is found on physical examination of the patient, urine tests and special investigations that produce images of the human body. These include:

  • IVU (intravenous urography): this shows the drainage system from the kidney, through the ureters, and down to the bladder. Most stones are found this way, and usually there are signs of a stone having been present even if one cannot be seen.
  • CT (computerised tomography): this shows the size and position of a stone, if there is one present. Almost always, stones are found except certain stones that are induced by treatment for HIV.
  • Ultrasound: this is not usually that useful at the start of renal colic, but sometimes may show the distension of a kidney that when a kidney has been blocked for several days
  • Ureteroscopy and retrograde pyelograms: these are tests performed under a general anaesthetic (asleep in an operating theatre). Treatment to remove the stone is often performed at the same time

The type of stone is important in determining the type of treatment, the chance of recurrence and the diet to reduce the risk of more stones. Stone analysis needs to be performed to do this.

What happens when a stone causes renal colic?

Some stones will pass spontaneously within a few hours or days. This is usually associated with some discomfort. Others may not pass at all. The chance or probability that a stone will pass on its own depends on the position of the stone within the urinary system and the size of the stone. The majority of stones pass themselves. In general, if stones have not passed within 4 weeks, most will need some form of medical intervention.

How are stones treated?

The pain of renal is treated by pain killers including drugs such as non-steroidal anti-inflammatory drugs (NSAID) such as diclofenac or opiates.

Sometimes, the stones will pass through without any direct medical interventions. This is determined by the size, position and how long the stone has been present. At other times, the stones are are treated by the following techniques;

  • conservatively (allow the stone to pass by itself)
  • Extracorporeal Shock Wave Lithotripsy (ESWL)
  • Ureteroscopy and stone fragmentation, possibly with a laser
  • Percutaneous Nephrolithotomy (PCNL)

In many situations, a tube is required to allow urine to flow from the kidney to the bladder. This tube is known as a JJ stent. It also allows the tissues to heal naturally. For more information, click here on JJ stents. If there is simultaneous infection and obstruction by a stone, then urgent relief of obstruction is required. A tube can be placed directly into the kidney through the back ('nephrostomy') tube.

What is the chance of a stone passing by itself?

The chance of a stone passing is largely determined by the size and position of the stone. Please see the table below, which shows the results from one study. The larger the stone, and the less the stone has progressed from the kidney down to the bladder, the less likely a stone will pass by itself.
 

 

Stone diameter (mm)

1-4

5-7

>7

All sizes

Position

of

Stone

Upper or proximal ureter

47%

63%

25%

48%

Mid-ureter

80%

0%

100%

60%

Lower or distal ureter

77%

71%

67%

75%

Vesico-ureteric junction

92%

50%

33%

79%

All positions

75%

60%

38%

77%


If a stone has not passed after 4 weeks, it is unlikely that a stone will by itself.

The safety of leaving a stone to pass by itself has to be judged by a doctor experienced in the management of urinary stones.

What is ESWL?

ESWL stands for extracorporeal shockwave lithotripsy. This is the treatment of choice for most stones. It is most often used for stones in the kidney itself or the upper ureter. The success rate drops as the size of the stone and the size of the patient increases. The stones are identified by X-rays or ultrasound and then shockwaves passed through the stone. Smaller fragments are created which are then passed in the urine. ESWL is performed whilst awake.

What is PCNL?

PCNL stands for percutaneous nephrolithotomy. Extremely large, hard or complicated stones are treated this way as maybe stones in abnormal kidneys. Under general anaesthetic, a tube is placed in the kidney and the stone broken with instruments passed through the tube.

What is ureteroscopy or uretero-renoscopy?

For stones in the middle or lower ureter and some stones in the kidney, ureteroscopy is an ideal choice. At other times, ureteroscopy is used when other techniques have been unsuccessful A special telescope designed to pass up ureter is used to find stones and then either either a tiny hammer or laser used to break stones.

How do you prevent more stones from developing?

It becomes more important to prevent more stones from developing, the more stones one has. In general, more fluid is recommended. It is important to know the type of stone that has been passed. For this, the stone must be sent for stone analysis so it is important to keep the stone if you can. For people with the most common stones (calcium oxalate), the recommend changes are shown on the stone diet page. Other types of stones may need different diets. Sometimes, drugs are recommended also to try and reduce the chance of more stones forming.

Surveillance after a stone may vary from one attendance to annual ultrasound or xrays.

What is ureteroscopy or uretero-renoscopy?

For stones in the middle or lower ureter and some stones in the kidney, ureteroscopy is an ideal choice. At other times, ureteroscopy is used when other techniques have been unsuccessful A special telescope designed to pass up ureter is used to find stones and then either either a tiny hammer or laser used to break stones.