Anyone who has ever passed a kidney stone will not forget the experience. It can be extremely painful. Some women have said that the pain is worse than childbirth. Not all kidney stones cause symptoms, however, and many are discovered when X-rays are obtained to evaluate for an unrelated condition. Even though these stones are pain free, they are important to diagnose before they grow too large to pass. Also, they may be discovered when someone is evaluated after finding blood in the urine. The pain develops when a kidney stone breaks loose and begins to work its way from the kidney toward the bladder through the connecting tube (ureter).
The incidence of kidney stones has been increasing in recent decades, perhaps because of diet choices and relative lack of fluids. Kidney stones affect up to 10% of Americans. Men tend to develop stones more than women because their urethra is smaller therefore women are able to pass the stones easier. Stones tend to develop in the middle years of life. More than half a million people will develop kidney stones in a year, and over one third of these patients will be hospitalized.
The kidneys are responsible for filtering out impurities as the blood flows through them. Minerals and other waste products are left behind to dissolve and eventually leave the body as urine. Occasionally the filtered minerals stick together and crystallize. These crystallized masses, referred to as kidney stones or renal calculi, can be as small as grains of sand or as large as golf balls. Kidney stones can also form in or travel to the ureter or bladder. A stone caught in the ureter can cause severe pain. If it becomes infected, it could lead to permanent kidney damage.
Although most small kidney stones pass down to the bladder without causing any permanent damage, it's important to determine the underlying cause so that more stones can be avoided in the future.
Stones form within the collecting system of the kidney. Many remain there indefinitely. Some stones break free into the urine and are propelled downward toward the bladder by the smooth muscle contractions of the ureter. These tube-like structures become narrower as they approach the bladder, making blockage by the stone possible even for relatively small stones.
One will not have signs and symptoms unless a kidney stone is large, causes a blockage, is causing infection or is being passed. The most common symptom is an intense cramping pain that can fluctuate in intensity over periods of five to 15 minutes. The pain usually starts in the back or side just below the edge of the ribs. As the stone moves down the ureter, the pain may radiate to the lower abdomen, groin and genitals. If the stone stops moving, the pain may stop too.
Other signs and symptoms may include:
» Bloody, cloudy or foul-smelling urine
» Burning during urination
» Persistent urge to urinate
» Nausea and vomiting
» Lower abdomen may be painful if touched
» Fever and chills if an infection is present
The crystals that lead to kidney stones are more likely to form when your urine contains a high concentration of certain substances — especially calcium, oxalate, uric acid and rarely, cystine. They may also form because of a low level of substances that help prevent crystal formation, such as citrate and magnesium. Crystals also may form if the urine becomes too concentrated or is too acidic or too alkaline.
A number of factors can cause changes in urine, including heredity, diet, drugs, climate, lifestyle factors and a variety of medical conditions. Each of the main types of kidney stones has a different cause.