Kidney Stones: what causes them?

  Kidney stones, also called nephroliths or uroliths, are small, hard aggregates of mineral and salt crystals that can form in any part of the urinary tract, but more frequently in the kidneys. Normally, minerals and salts contained in the urine do not form crystals, but are dissolved in the watery part of the urine due to the presence, in the urine, of certain substances that inhibit crystal formation. However, the ability of the urine to hold minerals and salts in solution is not infallible and when their concentration exceeds a given critical level, the formation of kidney stones may occur.

 Kidney stones formation is a two-step process: initially a submicroscopic crystal nucleus forms and precipitates from the solution. Then different crystal particles growth and aggregate to form a stone (or calculus) of variable size. The smallest stones are usually able to pass freely through the urinary tract to the outside of the body, while the largest ones are often retained within the urinary tract and usually need to be medically dissolved or surgically removed.  

 Typically symptoms appear when stones move from the kidney to the ureter, which is the small-diameter tube that connects the kidney to the bladder. The most characteristic sign is a severe pain in the lumbar region, spreading to the hip and the groin region as the stone passes through the urinary tract. Other symptoms and signs include nausea, vomiting, blood in urine, pain on urination and sometimes fever.

The importance of other factors in kidney stones

 Kidney stones can be caused by a variety of factors (genetic, dietary or infectious) and usually vary in their chemical composition depending on the cause. Calcium stones (which are usually composed mainly of calcium oxalate) are the most common stones among people. They typically result from an increased concentration of calcium or oxalate in the urine from a variety of causes, including an excessive intake of oxalate-containing foods (such as spinach, nuts, chocolate, potatoes, soy beans and strawberries), high intakes of vitamin D from supplements and certain digestive disorders which cause an increased absorption of calcium or oxalate from the intestine. Other types of kidney stones can result from urinary infections (struvite stones), dehydration or high-protein intake (uric acid stones) or certain hereditary metabolic disorders, such as cystinuria which causes an excessive excretion of the amino acid cystine in the urine leading to the formation of cystine stones.  

 The treatment* of kidney stones varies depending on the size of the stones and on how severe the symptoms are. When stones are small in size and cause no symptoms or only mild discomfort and pain, drinking 2-3 litres of water a day is usually enough to treat the condition, by allowing the stones to pass spontaneously. In this case, mild pain or discomfort caused by the passage of stones can be effectively controlled by taking pain relievers.

 However, when the stones are too large to pass or cause severe symptoms such as urinary bleeding or kidney damage, the treatment is usually more invasive and can involve the break-up of stones with sound waves (in order to reduce the stones to small fragments easily eliminable) or, alternatively, their surgical or endoscopic removal.

 Kidney stones are often recurrent. That is why most patients have to take preventive measures after treatment in order to avoid recurrence. Prevention of kidney stones usually involves lifestyle and dietary changes, such as drinking plenty of water each day, avoiding or limiting oxalate-rich foods, reducing animal protein in the diet and taking caution with calcium supplements. In addition, certain medicines (such as urine alkalinizing agents or antibiotics) may be prescribed by the doctor to lower the risk of kidney stones formation.

 People suffering from or at risk of kidney stones should have themselves covered with an appropriate international health insurance plan before kidney stones occur in order to cover the possible cost of therapeutic or preventive treatment in case you suffer from kidney stones.