Kidney stones

What are kidney stones?

Human urine contains dissolved waste products such as urea, creatinine and uric acid, as well as foreign substances, for example from medication. Under certain circumstances, these substances can form crystals and eventually become deposited as stones in the renal system. In most cases, the deposits consist of calcium- or phosphate-containing substances, and a kidney stone often travels through the urinary tract, coming to be known as a ureteric stone, bladder stone or urethral stone depending on its location. The collective term for all these stones is urinary stones. Some stones are no bigger than a pinhead, whilst others fill the entire renal pelvis. Small crystals can often be passed in the urine without being noticed and without causing any symptoms; symptoms usually only arise when the stones move into the renal tubules or the ureter. Once they reach a certain size, the stones can no longer pass through the urinary tract and block the flow of urine. In this case, the stretching of the tissue can lead to renal colic, characterised by severe, cramp-like pain. Kidney stones are regarded in industrialised countries as a ‘disease of affluence’, primarily caused by a high-protein diet, overeating, obesity and a lack of exercise. According to estimates, between five and ten per cent of the population in this country suffer from a kidney stone at least once in their lifetime. The risk of recurrence is high, and men are affected three times as often as women.

What is the composition of kidney stones?

Kidney stones consist of various types of crystalline materials, each formed by the accumulation of specific chemicals in the urine. The most common types of kidney stones are:

• Calcium oxalate stones: These are the most common (around 80 per cent of cases involve this type of stone) and consist mainly of calcium oxalate, and sometimes calcium phosphate. The stones range in colour from yellowish to black.
• Struvite stones: These often form in response to a urinary tract infection and consist of struvite, a mineral. These stones are significantly less common.
• Uric acid stones: These develop when the urine is too acidic, which is often caused by a high intake of animal proteins or certain metabolic disorders. Men are more likely to develop this type than women.
• Cystine stones: These are very rare and result from a congenital metabolic disorder. The stones consist of the amino acid cystine.

What are the causes and risk factors for kidney stones?

In general, kidney stones form when certain mineral salts are so highly concentrated in the urine that they crystallise and are deposited as stones. This happens, for example, when the body does not receive enough fluid through adequate drinking or loses too much fluid through sweating. The salts then become concentrated in the urine and can no longer dissolve. The causes of this are varied and are often linked to lifestyle factors. Other risk factors include:

• Disorders of uric acid metabolism (e.g. gout)
• Disorders of the parathyroid gland leading to increased excretion of calcium in the urine
• excessive consumption of meat and sausages
• excessive consumption of foods high in oxalic acid (e.g. spinach, cocoa, chocolate, black and green tea)
• rapid weight loss without adequate fluid intake
• Bedridden status (breakdown of calcium from the bones)
• Frequent urinary tract and renal pelvis infections
• Reduced excretion of substances that inhibit stone formation, such as zinc, magnesium and citrate, etc.
• Conditions that obstruct the flow of urine (e.g. kidney malformations)

What symptoms do kidney stones cause?

Generally speaking, the symptoms depend on the position, size, shape and mobility of the kidney stones. Small stones or grit-like particles usually cause no or only mild discomfort and can be flushed out of the urinary tract if the patient increases their fluid intake. Even stones that lie quietly in the kidney are usually asymptomatic and are often only discovered by chance, for example during an ultrasound or X-ray examination. Sometimes, a pulling or pressing sensation in the flank area or a small amount of blood in the urine may indicate a kidney stone. Larger kidney stones that block the flow of urine in the urinary tract can cause very severe pain; this is because if the renal pelvis or ureter is blocked, or if the stones start to move and slip into the ureter, renal colic may occur. This usually begins very suddenly and causes the following symptoms:

• cramp-like and spasmodic pain in the kidney area, radiating to the genitals, thighs and groin
• Nausea and vomiting
• Anxiety and restlessness

Renal colic can last for a few minutes or even hours and must be treated by a doctor as soon as possible to prevent permanent damage to the kidneys and urinary tract. Another complication associated with this condition is complete ureteral obstruction. In this case, the kidney continues to produce urine initially, but the filtered toxins accumulate in the retained urine within the kidney and damage the kidney tissue. Furthermore, due to the accumulated urine, bacteria can enter the urinary tract and establish themselves there. In the worst-case scenario, bacteria can enter the bloodstream as a result of urinary retention and infection, which can lead to life-threatening urosepsis (an acute infection caused by bacteria from the urogenital tract). In some cases, this can also lead to atrophic kidneys (shrunken kidneys), in which kidney tissue is destroyed.

How are kidney stones diagnosed? 

A diagnosis of a kidney stone can often be made based on the course of the illness, the pain and tenderness in the kidney area. Furthermore, a urine test is carried out to detect blood in the urine, any infections or signs of kidney damage. A blood test allows the levels of calcium, uric acid and other substances to be determined and kidney function to be assessed. In addition, an ultrasound scan or a CT scan can confirm the diagnosis, and an X-ray of the kidney, ureter, bladder and prostate may be used to diagnose the stone. If necessary, an X-ray examination of the ureter and renal pelvis using a contrast agent may also be carried out. An analysis of the stone’s chemical composition should always be performed.

How are kidney stones treated?

Many kidney stones are passed spontaneously in the urine. In some cases, this may even occur with medical support following a bout of renal colic. Options for pain management include local heat (full baths, hot water bottles, warm, damp compresses), physical activity (climbing stairs, hopping, etc.) and increased fluid intake. Painkillers or anti-inflammatory and analgesic medication (NSAIDs) may also be used. However, such conservative treatment is not indicated or must be discontinued if:

• colic or infections occur during treatment
• the diameter of the stones exceeds eight millimetres
• severe colic cannot be controlled by medication
• urinary retention occurs
• a febrile urinary tract infection develops

In these cases, there are various methods of active stone removal: Extracorporeal shock wave lithotripsy: This involves breaking up the kidney stones without surgery by applying shock waves, after which the fragments are passed naturally. Minimally invasive stone treatment: There are various methods here, which may be percutaneous, endoscopic or laparoscopic and are all very gentle techniques. If neither shock wave therapy nor endoscopic stone removal is successful, the laparoscopic method is used. In this procedure, the surgical instruments are inserted via the abdominal cavity. Surgical stone removal: This method, which involves open surgery, is now used only very rarely, for example in cases of very large stones that completely fill the renal pelvis.

How can kidney stones be prevented?

As kidney stones can recur, prevention is particularly important. The following measures help to prevent kidney stones or avoid recurrence:

• Avoid being overweight
• Limit your intake of animal proteins
• Drink plenty of fluids (especially after heavy sweating)
• Use salt sparingly
• Take regular exercise

Which doctor should I see if I suspect I have kidney stones?

To have your symptoms investigated, you can either see a GP or a specialist in urology.