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.
Most kidney stones form because some individuals are genetically predisposed to this condition. In other words, it is not usually a specific disease which causes stones, it is usually just bad luck. A minority of stones occur because of a specific condition, such as hypercalcaemia ( high levels of calcium in the blood). Other conditions which may increase the likelihood of stone formation include: urinary infections, gout, bowel disease or surgery and many other uncommon metabolic conditions.
Most kidney stones initially cause no symptoms at all. Symptoms usually start when a stone in the kidney passes downstream into the ureter and causes a blockage in the system. This leads to “renal colic” which is severe pain, usually in the back or the side, but sometimes also in the front of the abdomen. This pain may be associated with nausea and vomiting. Other symptoms from stone disease include blood in the urine, urinary frequency and urinary infection. Some patients with a stone trying to pass become very unwell, and many end up resenting to the emergency department.
Most episodes of painful kidney stone disease require a CT scan for an accurate diagnosis. Other forms of imaging include a plain X Ray or an Ultrasound, but these are less reliable. Patients presenting with kidney stones also require blood and urinary tests to make sure there is no infection and that the kidneys are functioning normally.
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. Severe pain often requires an injection of morphine as well as anti-inflammatory agents. 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 with imaging taken for another reason. In such situations, a wait-and-see course may be appropriate if the stone is less than 5mm in diameter. As a rough guide , a 5mm has 50% chance of passing, and larger stones are unlikely to pass with intervention. 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 imaging 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 2 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 general anaesthesia 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 are about 75% depending on the individual circumstances. ESWL is very safe, the least invasive procedure, but usually is suitable for patients with a painless stone which is still in the kidney.
Most stones in the ureter and stones in the kidney are now treated with ureteroscopy. This involves the passage of a fine telescope through the urethra, beyond the bladder and up to the stone in the ureter or kidney. No incision is required. When the stone is visualised, it can be fragmented using a laser into tiny pieces and larger fragments can be extracted with a basket. Following this procedure, a stent (hollow fine tube) needs to stay in the ureter for a couple of weeks to keep the kidney unobstructed. The stent can later be removed in a minor procedure. Sometimes a stent needs to be placed first in order to dilate the ureter so that the scope can reach the stone safely when returning to theatre a week or two later. Ureteroscopy has a much higher success rate compared to ESWL, but it does require a second procedure to remove the stent.
This procedure is used for larger stones in the kidney. It involves an incision in the skin and insertion of a telescope through the incision into the kidney. Stones are then fragmented and removed through the telescope. This is a more invasive procedure than ESWL or ureteroscopy and requires hospitalisation for 2-3 nights.
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
Most kidney stones cannot be dissolved. Some 5% of kidney stones are made up of Uric Acid, and these may be able to be dissolved by changing the acidity of the urine. Patients need to take a medicine such as Ural which will make the urine less acidic as this aids the stone to dissolve.
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 –or enough to make 2-3 litres of urine/day. This must be increased in hotter weather and during physical activity. It does not seem to matter which fluid is consumed, hence juice, mild, tea or coffee are equally as effective as water.
2. Maintain a balanced diet. The current recommendation is to aim for a HIGH calcium diet (which surprisingly reduces the likelihood of calcium stones). The diet should also be low in salt and low in protein.
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.