All About Kidney Stones

A kidney stone (nephrolithiasis) is a solid piece of material that forms in the kidney. It is made from substances that normally dissolve in the urine. Each year, about 1 million people in the U.S. get kidney stones.

Kidney stones are more common in whites than in African Americans. They typically strike between age 20 and 50 and are more common in men than women. If you get one stone, you are more likely to get more. Repeated stone attacks can affect your kidneys.

How stones form

Your urinary tract is made up of several parts:

  • Kidneys. These are 2 bean-shaped organs about the size of your fist.

  • Ureters. These are 2 narrow muscular tubes that drain urine from the kidneys into the bladder.

  • Bladder. This organ temporarily stores urine.

  • Urethra. This is the tube that empties urine from the bladder.

The kidneys make urine by removing extra water and waste from your blood. They also help your body balance certain chemicals in your blood.

Kidney stones are made up of chemicals in your urine. These include:

  • Calcium

  • Oxalate

  • Phosphate

  • Uric acid (urate)

  • Cystine

  • Struvite

Stones begin as crystals that build up inside the kidney. Small crystals can pass from your body through the urine without you ever knowing about them. When the crystals grow larger and become stones, they can get stuck in the ureter and block the flow of urine. This causes infection and pain.

About 3 in 4 kidney stones contain calcium plus either oxalate or phosphate. A less common type of stone is caused by urinary tract infections. It is called an infection stone (struvite). It is made of magnesium ammonium phosphate. Struvite stones make up 1 to 1.5 in 10 kidney stones. About 1 in 10 of the remaining stones are made of uric acid. Uric acid is made from purine. This is a nitrogen compound found in protein and made in your liver. Less than 3 in 100 stones are made of the amino acid cystine.

Stones can be as small as a grain of sand or as large as a golf ball.

Salts in the urine

Healthcare providers don’t really know what causes kidney stones to form. Some people are more likely to get them because of their family history of stones. But in most cases, they are caused by having too many salts in your urine. These salts are calcium oxalate, uric acid, and cystine. Salts can build up in the kidney when you don’t have enough urine or you have higher levels of the salts than normal. When the salts build up to a certain point, they no longer dissolve. They form crystals instead. Normally, the urine contains chemicals and enzymes that keep crystals from forming, or from sticking to the inner surface of the kidney.

Certain conditions make it more likely that you will get kidney stones. Those conditions are:

  • Digestive disease

  • Kidney disease

  • Urinary tract infections

  • Metabolic disorders such as hyperparathyroidism

In other words, changes in the way your body uses food and beverages can increase your chances of growing crystals and getting kidney stones. Some types of kidney stones run in families (hereditary).

Other causes

Some rare disorders can cause kidney stones. Some of those disorders are:

  • Renal tubular acidosis. This is sometimes an inherited disease.

  • Cystinuria. This means that crystals of cystine form.

  • Hyperoxaluria. This means that crystals of oxalate form.

  • Absorptive hypercalciuria. This means that your body takes in too much calcium from food.

  • Chronic dehydration. This occurs from not drinking enough water.

Kidney stones are more common in people with high blood pressure. They are also more common in people who have a disorder of uric acid metabolism (hyperuricosuria). Stones are also common in people who:

  • Have gout

  • Take in too much vitamin D

  • Have a blockage or infection of the urinary tract

  • Take certain water pills (diuretics) or calcium-based antacids

  • Have inflammatory bowel disease such as Crohn's disease or ulcerative colitis

  • Have had an intestinal bypass or ostomy surgery

Making a diagnosis

There are no true "warning signs" for kidney stones. Small stones are usually passed unnoticed. Large stones often remain undetected until they become lodged in the ureter and you have severe and sudden pain in the back or lower abdomen. The pain is usually described as a sharp and cramping pain in the back, the side, or the lower belly (abdomen). The pain may spread to the groin. There may also be blood in the urine, nausea, and vomiting. If the stone is too large to pass, the muscles of the ureter tighten trying to squeeze the stone into the bladder. Fever or chills usually mean there is an infection. Sometimes stones stay in the kidneys and grow larger.

Most kidney stones can be diagnosed by an X-ray. A sonogram can also spot a stone. These images tell your healthcare provider the stone's size and location. Blood and urine tests help find any abnormal substance that might help stones form. Some imaging tests can see if fluid is backing up in the kidneys that could cause damage.

Your healthcare provider may decide to scan the urinary system using a CT scan or a special X-ray test called an intravenous pyelogram (IVP). The results of these tests and the others above help your healthcare provider figure out the right treatment for you.

Getting the stone out

In most cases, treatment means letting the stone pass naturally. Your healthcare provider may give you medicine for pain relief. Then he or she will add fluids until the ureter builds up enough pressure to push the stone out. You will usually be asked to catch the stone in a strainer so it can be looked at in the lab. If the stone hasn't passed in 8 to 12 hours, you may need to see a urologist to push the stone back to the kidney so it can be broken up.

For stones that don't pass on their own, other treatments are used:

  • Extracorporeal shock wave lithotripsy (ESWL). This treatment uses an ultrasound machine to send shock waves through the skin and body tissue toward the stone. The shock waves break the stone into small pieces that can pass from your body in the urine.

  • Percutaneous stone removal. This treatment is used for stones that are too large or that can't be reached with ESWL. A surgeon makes a small incision in your back and makes a tunnel to the kidney. The stone is then taken out through a nephroscope. If the stone is very large, the surgeon can put an energy probe in to break the stone into smaller pieces and then remove the pieces.

  • Ureteroscopic stone removal. The surgeon puts a fiber optic tool into the urethra and the bladder. He or she then moves it into the ureter. After the stone is found, the surgeon removes it with a cage-like basket device or shatters it with laser beams or shock waves. Often, the surgeon puts a stent in the ureter to keep the tube widened and ease passing of the stone pieces.

100 ounces of prevention

The best treatment for kidney stones is to not get them in the first place. If you've had a kidney stone in the past, you are likely to form another. That's why prevention is important. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) says the therapy your healthcare provider gives you will depend on the type of stone you have. For example, a medicine that helps prevent calcium stones will not work if you have a struvite stone. The diet changes that help prevent uric acid stones may have no effect on calcium stones. So careful analysis of the stone will help guide your treatment.

If you are overweight, losing weight may help.

The most important part of prevention is getting plenty of fluids. This dilutes your urine and increases urination. More trips to the bathroom help remove extra chemicals from the urine and kidneys. This lowers the chances of stone formation.

Kidney experts recommend that you drink at least 100 ounces of fluid every day. Their drink of choice? Water. Water is available to everyone and is inexpensive.

People who form kidney stones were once told to stay away from dairy products and other foods that contained a lot of calcium. Recent studies have shown that foods high in calcium actually help prevent stones, according to the NIDDK. But calcium supplements may increase the risk of developing stones.

Eat less protein

For some people, eating less protein, especially protein from meat, may help prevent certain stones. Protein can increase uric acid, calcium, and oxalates in the urine. Protein also reduces citrate.

If you are at risk for uric acid stones, you may be helped by eating fewer foods that contain purines. These foods include sardines, yeast, and organ meats.

If you are a person who absorbs a lot of oxalate, you should not drink large amounts of tea, because it has a lot of oxalate. You should also drink less or no alcohol. Other foods to pass up include chocolate, beets, coffee, cola, nuts, rhubarb, spinach, strawberries, and wheat bran.

Your healthcare provider may prescribe medicine to help prevent kidney stones. The medicines control the amount of substances in the urine that form crystals or prevent the infections that can lead to stone growth.

You should also limit how much salt (sodium) you get each day. Salt is another chemical that must leave the body through the urine. The more chemicals that are in the urine, the more likely you are to form a stone.

Are you at risk?

Things that may increase your chance of developing kidney stones are:

  • A family history of stone formation

  • An inherited condition that causes the body to absorb too much calcium

  • A low level of citrate in the urine. This may help calcium stones form.

  • Overactive parathyroid glands

  • Urinary tract infections

  • Gout

  • Bowel disease

  • High blood pressure