Urinary stones (calculi) are hardened mineral deposits that form in the kidney. They originate as microscopic particles and develop into stones over time. Urinary stones may contain various combinations of chemicals. The most common type of stone contains calcium in combination with either oxalate or phosphate.
Other stones may form from uric acid – the chemical that causes gout (a type of arthritis). A less common type of stone is caused by infection in the urinary tract. This type of stone is called a struvite or infection stone. Other rare stones include cystine stones, which form due to a specific metabolic abnormality.
Urinary stones usually arise because of the breakdown of a delicate balance. The kidneys must conserve water, but they must also excrete waste materials that have a low solubility (i.e. do not dissolve easily). These two opposing requirements must be balanced during adaptation to diet, climate, and activity. Urine contains a number of chemicals which act as “stone inhibitors”, allowing the concentration of substances such as calcium in the urine without stone formation. For reasons not well understood, these protective mechanisms work less well for some people, putting them at risk of stone formation when the urine is concentrated. When the urine becomes supersaturated (i.e. contains more chemicals than can be dissolved) because excretion rates are excessive and/or because water conservation is extreme, crystals form and may grow and aggregate to form a stone.
The first symptom of a kidney stone is often extreme pain. The pain often begins suddenly when a stone moves in the urinary tract, causing irritation or blockage. Typically, a person feels a sharp, cramping pain the back and side in the area of the kidney or in the lower abdomen. Sometimes nausea and vomiting occur also. Later, the pain may spread to the groin. If the stone is too large to pass easily, the pain continues as the muscles in the wall of the narrow ureter try to squeeze the stone along towards the bladder. As a stone grows or moves, blood may be found in the urine. As it moves down the ureter closer to the bladder, a person may also feel the need to urinate more often. If fever and chills accompany any of these symptoms, an infection may be present. In this case, a doctor should be contacted immediately.
X-ray is the chief method used to diagnose kidney stones. A CT scan of the abdomen gives excellent pictures of the urinary tract, as well as other intra-abdominal organs and will give information as to the site and size of the stone
The severe pain of renal colic needs to be controlled by strong pain-killers. It is best to seek help from your local doctor, or the nearest emergency department. It is also possible that the pain may be caused by some other problem needing immediate attention.
Not all urinary stones cause pain. In some patients, they are found incidentally on X-rays taken for another reason. In such situations, a wait-and-see course may be recommended by the doctor. As a rough guide a stone less than 5mm has an 80-90% chance of passing, a stone 5-10mm has a 40-50% chance, and a stone over 10mm in size has minimal chance of passing itself. Unfortunately, it is impossible to predict how long this could take. Medications may be given to assist the ureter in expelling the stone by altering the tone of the muscle wall of the ureter. An example is tamsulosin (Flomaxtra), which can be taken daily and may increase the chance of the stone passing over a shorter period of time.
If conservative management is chosen initially, it is important to note that:
1. Passage of stone through the urethra is rarely painful In fact, most people will not notice it. This is because the urethra (the tube draining the bladder) has a wider calibre than ureter (the tube between each kidney and the bladder) that the stone has travelled down. Therefore if it has made it down to the bladder, it will easily flush out with the passage of urine. For this reason it is important to sift your urine, otherwise you are unlikely to be aware of the stone passing.
2. Just because the pain has gone doesn’t mean the stone is no longer there It is possible to have silent or painless obstruction from a stone that if not recognized, can lead to gradual failure of the blocked kidney. It is therefore imperative to have follow-up X-rays to be absolutely sure the stone has gone if you have not noticed it pass in the urine.
Ongoing pain, failure to pass the stone after around 4 weeks, reduced kidney function, a single kidney, or infection are reasons to abandon conservative management and intervene to remove or dissolve the stone. Once it is decided that active treatment of the stone is required, there are several options depending on the type of stone, the size of the stone, and its location.
ESWL (Extracorporeal shock wave lithotripsy)
This is shattering of a stone with shock waves produced outside the body. The treatment is administered under anaesthesia (spinal or general) as a day case. The stone is broken into very small fragments (resembling sand) which are passed in the urine. Its effectiveness depends upon stone composition, stone size, and stone location within the urinary tract. Success rates therefore vary from over 90% to under 60% depending on the individual circumstances.
Surgical removal of urinary stones
Endoscopic Ureteric stones can be removed by passing a fine telescope, called a ureteroscope, through the urethra under anaesthetic and into the ureter to locate the obstructing stone. The stone can then be broken up into fragments, often using a laser, and the pieces removed. Very fine ‘flexible ureteroscopes’ can be passed all the way into the kidney and used to reach and fragment very high ureteric or kidney stones, although it is usually not possible to treat large kidney stones in this way.
Percutaneous (via the skin)
For stones within the kidney that are too large or unsuitable for ESWL a telescope can be passed directly into the kidney through a small (1cm) skin incision in the back to break up and remove the stone(s). This can allow removal of large or multiple stones, and can be repeated if necessary to reach all parts of the kidney and ensure all stone is removed.
An open operation is rarely needed nowadays because of the multiple minimally invasive options, but may occasionally be necessary e.g. for very large stones, abnormal kidney anatomy, or other abnormalities that need correcting at the same time as stone removal.
Dissolving uric acid stones
Stones caused by high levels of uric acid (the chemical causing gout) are not visible on standard X-rays and can grow to large sizes. Uric acid is a breakdown product of a protein called purine which is excreted in the urine. When too much uric acid is produced and the urine is acidic, uric acid stones form in the urinary system. High levels of uric acid in the blood can also lead to the formation of gout. It is possible to dissolve these stones over a period of weeks-months (depending on the size) using the following dissolution treatment:
1. Maintain urine pH Alkalinising (making less acidic) the urine, using an agent such as Ural or Citravescent, allows much more uric acid to dissolve in the urine. The urine acidity can be measured daily with a pH indicator strip (available in pharmacies) and the dose of alkalinizing agent can be altered accordingly.
2. Lower blood uric acid levels Allopurinol, a medication that reduces uric acid production, is prescribed. Reducing intake of alcohol, foods high in purine content, and losing weight can also reduce uric acid levels.
3. Increase fluid intake Drink enough fluid (but not alcohol) to keep your urine a light straw colour to allow more uric acid to dissolve into the urine.
How can I prevent future stones forming?
For patients presenting with their first urinary stone, a basic metabolic analysis should be undertaken. This consists of blood and urine tests, and analysis of the stone composition (if possible). Most patients will not have any detectable abnormality, and approximately half of these people will not form any further stones in the short term. For this reason there is no specific treatment or further investigation recommended, and the following basic advice is given to reduce the risk of stone recurrence:
1. Keep adequately hydrated. Stones form in concentrated urine. Therefore it is important to ensure your fluid intake is enough to keep the urine a light straw colour – usually around 6-8 glasses of water/day or enough to make 2-3 litres of urine/day. This must be increased in hotter weather and during physical activity. Get into the habit of carrying a water bottle to avoid long periods without fluids.
2. Maintain a balanced diet Trying to avoid all foods containing calcium or oxalate involves a complicated diet that for most is not feasible, and may not actually reduce the risk of stone formation considerably. It is better to simply to follow a balanced diet, and avoid excesses of calcium or oxalate containing foods (e.g. no more than 3 glasses of milk/day). This should include minimizing salt intake (avoid adding salt at the table) and avoiding a high protein (meat-containing) diet.
3. Increase intake of dietary fibre There is some evidence that increasing dietary fibre can reduce absorption of stone forming chemicals. Such a dietary modification may not only reduce the risk of stone recurrence, but will also benefit general health by reducing the risk of heart disease, high blood pressure, and colon disease.
For patients with recurrent stones despite the above measures, more in-depth metabolic analyses can be undertaken, and medication regularly taken to reduce concentration of stone-forming substances in the urine.
For a consultation with one of our urologists, please call AUA on 03 8506 3600.