Kidney and Bladder Stones
What are the facts about Kidney Stones?
Kidney stones are common, and the incidence of these has been increasing since the start of the 20th century such that kidney stones are found in approximately 8% of patients (one in twelve) who undergo CT imaging representing the approximate likelihood of having an “incidental” stone. The chance of presenting with a symptomatic episode during a person’s lifetime is approximately one in eleven. Men are slightly more commonly affected than women, with the risk greater for Caucasians than other racial groups. Patients of all ages can suffer from stones, although the peak age for the first stone is around 45 years old.
Most stones are made out of the following types of biochemical composition:
- Calcium StonesThis is the most common type of kidney stone. This includes Calcium Oxalate stones and Calcium Phosphate stones. Mostly the stones are a mixture of both, and are usually predominantly calcium oxalate, which is the commonest stone composition overall, owing to the fact that these chemicals are very insoluble when mixed together in the urine.
- Struvite StonesThese are also known as “infection stones” or “triple phosphate stones” (i.e. made of calcium, magnesium and ammonium phosphate). These stones are slightly more common in females than males, and, as the name implies, are often associated with urinary tract infection. Specifically, infections with certain bacteria that can metabolise urea (one of the key waste products in the urine) into ammonia, which makes the urine alkaline (and accounts for the strong smell in this kind of infection). This affects the solubility of calcium phosphate, such that very large stones can grow, branching to fill the whole of the collecting system of the kidney – these stones are therefore known as “staghorn” stones, and are the most challenging stones to treat effectively.
- Uric Acid StonesThese tend to have a smooth surface and golden colour and form in an acidic urine. These are more common in people who eat a diet which is rich in animal protein and are also seen in patients with the metabolic syndrome (see below) whose urine tends to be disproportionately acidic.
- Cystine StonesThis is a genetic condition, and although a rare cause of stones overall (accounting for approximately 1% of stone formers) patients who make cysteine stones are often young when they make their first stone, and have a strong tendency to have many recurrent episodes and require multi-disciplinary care not only to treat their stones but to help to prevent further episodes with careful fluid and medical management.
Risk Factors for Stone Formation
Amongst many important roles controlling the internal environment of the body, the kidney deals with waste products of metabolism, excreting these from the blood that passes through the kidney into the urine, such that these “waste products” can be eliminated from the body. Stone formation occurs if there is an excess of certain of these stone-forming substances if they are not balanced out by the presence of other urine constituents that inhibit stone formation and, most importantly, are not dissolved into a large enough volume of urine overall that they are sufficiently dilute to avoid crystallising into a stone. It is for this reason that the key advice to all stone forming patients is to drink more fluid, particularly water, to ensure that their urine is adequately dilute that the risk of stone formation can be reduced.
Stone formation is governed by both intrinsic (heredity, age & sex) and extrinsic factors (geography, climate, water intake & diet). A diet that has a high animal protein content, containing a lot of refined sugar and salt increases the risk of forming stones, particularly if this is accompanied by a poor fluid intake. Some patients have anatomical factors relating to the structure and drainage of their kidneys that also affect the risk of stone formation – these will often be apparent on a CT scan and will be factored into the decision making for any active treatment suggested by your Urologist.
Signs and symptoms of Kidney Stones
Stones are produced from the constituents of the urine which have crystallised when the urine is concentrated and have then enlarged over time (with the addition of more crystals in a similar process to the enlargement of a stalactite or stalagmite in a cave). Whilst these stones are in the kidney, they may not cause any symptoms at all, and might be detected as an incidental finding on an imaging test performed for some other reason. Alternatively, they may cause an ache in the loin, blood in the urine (usually this is “non-visible haematuria” may be detected when the urine is examined by dipsticks or microscopy) which may be a potential cause or risk factor for developing a urinary tract infection.
It is when stones that have been sitting in the kidney move into the ureter (the tube that drains urine produced in the kidney for storage in the bladder) that their presentation is obvious and dramatic. This is known as acute ureteric colic, and is an extremely painful condition often associated with nausea and vomiting. This pain usually develops in the loin, and then can be felt to move or radiate towards the groin or the testis / labia as the stone moves from higher up by the kidney to lower down by the bladder. When the stone gets very close to the bladder (at the “VUJ – the vesico-ureteric junction, where the ureter passes into the bladder itself) there may be lower urinary tract symptoms such as a desire to urinate but with very little to pass – this is due to the stone stimulating a part of the bladder that is quite sensitive, making the brain believe it is due to a full bladder, but is in fact due to the presence of a stone instead. Stones in this position may also cause as sensation of burning when passing urine, or pain at the tip of the penis / urethra, or even a sign of visible blood in the urine.