Kidney stones occur in 1/11 people during a lifetime. The number of people forming stones has doubled in the past 15 years. A person who has had a kidney stone has a 50 percent chance of forming another stone over 5-10 years. The good news is that for many people, another kidney stone can be prevented or the number reduced by simple measures.
What Causes Kidney Stones?
Kidney stones grow from crystals that form in the urine. This occurs when there is too much of a salt that can form a crystal, too little of a substance that can stop a crystal forming, or too little fluid to keep the crystals from forming. Crystals grow into stones. For all kidney stones, too little fluid in the urine is a major factor allowing the stones to form.
The Different Types of Kidney Stones
There are many different kinds of kidney stones. The most common kind is made of calcium and some other chemical such as oxalate or phosphate. Less common are stones made of uric acid, cystine or a combination of different elements. Size varies from a pin head to a golf ball. A quarter inch stone is the largest that can pass from kidney to bladder and out in urine.
Who is at Risk?
Stones occur more commonly in men and in those with other family members who have had kidney stones. Environmental influences including geography and diet can also play a role. Dietary factors include too much salt, soda, calories and meat. Diets high in fruits and vegetables provide a lower risk for stones. Certain medical conditions such as the metabolic syndrome, some weight loss surgeries, urinary tract obstruction or recurrent infection in the urine make people more likely to form stones. Stone provoking medications include excessive amounts of calcium, antacids, vitamins C and D, and medications for certain diseases.
Kidney Stone Symptoms & Treatment
People who have kidney stones may have no symptoms if one or more small stones remain in the kidney(s). However when kidney stones are passed from the kidney to the bladder they can cause mild discomfort if they are small or severe pain in the loin, groin and lower abdomen if they are large. There may be blood in the urine. Stones, too large to pass, can cause very severe pain and vomiting. If there is accompanying infection, a person may have fever and chills.
Most, but not all stones can be seen with regular X-rays, all can be detected with ultrasound or CT scans. If a stone is not passed and is blocking the urinary passages, it can be removed with a cystoscope or by breaking it up into small pieces with lithotripsy or a laser. These procedures are carried out by a urologist.
After a stone is passed or removed, it should be sent for analysis. Knowing the stone composition and the chemical composition of urine collected over 24 hours helps identify strategies to prevent the formation of more stones.
To prevent recurrence of kidney stones, a person should drink 2-3 quarts (liters) of fluid each day to keep the urine very dilute. This should be done not just throughout the day but before going to bed and during the night if awake. The goal is to have pale colored urine all the time including in the early morning. Those with a kidney, heart or liver condition where fluid intake is limited, should discuss the amount they can drink with their doctor.
Although too much calcium in the diet can cause kidney stones, so can too little. It is recommended that all people include foods rich in calcium in their diet whether or not they have kidney stones. Those with a tendency to form calcium kidney stones should reduce salt and protein in the diet and try to eat a lot of fruit and vegetables but avoid excess almond products. Other dietary restrictions are based on stone composition.
In addition, some people may require medications to reduce the substances that form crystals or increase the substances that stop crystals forming. Commonly used medications are thiazides to reduce calcium in the urine, allopurinol to reduce uric acid in blood and urine and potassium or calcium citrate to increase citrate (which is an inhibitor of stone formation) in the urine.
When possible, people who form kidney stones should drink a lot of water around the clock. This is the most effective proven preventive strategy, is inexpensive, and inconvenience is the only side effect.
Virginia L. Hood, MBBS, MPH, MACP, is a nephrologist at the University of Vermont Medical Center and a professor at the Larner College of Medicine at UVM.