The kidneys play an important role in eliminating body waste. This waste usually remains dissolved in the urine as it passes through the kidney drainage system (calices, pelvis and ureter). Kidney stones are crystalline particles that form in the urine, often producing pain when they prevent the evacuation of urine from a kidney.
In Canada, about one in ten people will have kidney stones in their lifetime. This problem is more common in men than in women and rarely affects children. In most adults, it is not thought that the formation of a kidney stone is hereditary even if several family members have had stones. Children with kidney stones, however, have probably inherited a greater risk. Some children are affected by severe forms of stone disease (where stones are formed) that require in-depth examinations and regular monitoring.
Formation of kidney stones
Kidney stones are formed when the concentration of certain substances in the urine exceeds the amount that can remain dissolved. This can happen when the urine becomes too concentrated because of its low volume or because of the excessive excretion of certain substances.
A small volume of urine may be caused by insufficient fluid intake or excessive fluid loss due to eg heavy perspiration or chronic diarrhea. Similarly, urine can be overloaded with a substance when it is ingested too much, when the body produces too much, or when the functioning of the intestines or kidneys changes. Kidney stones are rarely a sign of kidney damage and stone formation is rare in people whose kidneys function poorly.
Most of the time, it takes several months or years for the kidney stones to grow enough to produce symptoms, usually by obstructing the evacuation of urine from a kidney. Occasionally, stones can form more quickly. Because calculi usually do not cause symptoms soon after their formation, it is impossible to know how quickly the calculus (s) formed. About 50% of those who developed a calculation will develop another less than 10 years later and 75% less than 20 years later.
Types of calculations
Most kidney stones contain calcium, usually calcium oxalate or calcium phosphate. About 10% of kidney stones are composed of uric acid, a byproduct of the digestion of meat, poultry and fish, which is excreted in greater concentration in people with gout. Some stones (struvite stones) are associated with some bacterial infections of the urine.
Examination of kidney stones
Most kidney stones can be seen on plain X-rays. Uric acid stones, however, are not visible on plain radiographs and require other methods. Intravenous urography is often used when pain suggests the presence of a kidney stone. This involves the injection of a dye that is excreted in the urine, showing the appearance, function, and evacuation of the kidneys. Urography is useful for detecting the location and size of a calculus causing kidney obstruction.
Ultrasound and computed tomography (CT-scan) are useful to diagnose a calculation in some people. Examinations of urine and blood help monitor kidney function and determine the cause of kidney stone formation. The number and complexity of the recommended tests depends on the severity of the gallstone disease, the number of calculations made in the past, and the age of the person when the first calculation was made.
Treatment of kidney stones
Treatment of kidney stones is sometimes necessary to relieve pain or obstruction. Many stones go by themselves in the urine without specific treatment. Shock waves produced outside the body are occasionally used to break a large computation into small particles that will be evacuated more easily. It is often possible to remove a calculus blocked in a ureter with instruments introduced through the urethra (urinary canal between the bladder and the outside). It is sometimes necessary to remove some larger or recalcitrant stones with small skin incisions (percutaneous surgery) but rarely with traditional incisions. It is possible that not all of these treatments are available at your hospital.
Prevention of kidney stones
The main way to prevent kidney stones is to increase fluid intake so that the urine is always well diluted. Although it is recommended that all people with stones try to produce two to three liters of urine a day, any increase in the amount of fluid consumed is beneficial. You should drink more when there is fluid loss due to heavy sweating or diarrhea.
About half of your fluid intake should ideally be water. There is no definitive evidence that hard water is less effective than fresh water in helping to prevent kidney stones. Almost all liquids help reduce the risk of stone formation. Some fluids such as iced tea, cocoa and cranberry juice may contain substances found in many kidney stones. These liquids are less useful for preventing stones.
A drastic restriction of dietary calcium intake is not recommended for the prevention of kidney stones and may even worsen stone formation in some people. Limiting calcium can also increase the risk of developing bone problems in older people. You should not reduce your calcium intake without consulting your doctor.
An important constituent of many calculations is oxalate. The body produces almost all the oxalate found in the urine as a by-product of metabolism, while a small portion comes from the diet. There are high levels of oxalate in spinach, rhubarb, cranberries, strawberries, blackberries, chocolate, nuts, beet greens, squash, cocoa and tea. People with Calcium Oxalate Calculation should avoid consuming these foods in large quantities.
A diet rich in protein found in meat, fish and poultry increases the risk of stone formation. This applies to uric acid calculations, but also to calcium calculations. Your animal protein intake should be limited to 250 grams (eight ounces) a day.
Significant salt intake is associated with increased excretion of calcium in the urine, even if the salt does not contain calcium. A salt restriction is recommended for people affected by recurrent stones. A diet rich in fiber can bring additional benefits.
It is important that these dietary changes are permanently introduced into the lifestyle. These changes should be gradual, starting with increased fluid intake and reduced dietary salt intake. When these habits are taken, other dietary changes may be introduced if calculus formation remains a problem.
All people affected by kidney stones should have some form of medical supervision. The duration and manner of monitoring may vary depending on the opinion of the urologist and the severity of the affected person’s gallstone disease. In most cases, an annual x-ray (no dye injection) or ultrasound of the kidneys is sufficient. Any changes to the diet, medications and health plan can be evaluated at this time. Tighter monitoring may be necessary for some people with special conditions, in children and in people with kidney abnormalities.