Kidney stones (renal lithiasis) are small, hard deposits of mineral and acid salts on the inner surfaces of your kidneys. Normally, the substances that make up kidney stones are diluted in the urine. When urine is concentrated, though, minerals may crystallize, stick together and solidify. The result is a kidney stone.
it’s important to find out what type of kidney stone you have and why it developed. Some of the underlying causes of kidney stones can be treated to prevent new stones from forming.
Your kidneys are two bean-shaped organs, each about the size of your fist. They’re located in back of your abdomen on each side of your spine, and their main function is to remove excess fluid, unneeded electrolytes and wastes from your blood in the form of urine. The ureters carry urine from your kidneys to your bladder, where it’s stored until you eliminate it from your body.
Kidney stones form when the components of urine fluid and various minerals and acids are out of balance. When this happens, your urine contains more crystal-forming substances, such as calcium and uric acid, than the available fluid can dilute. At the same time, your urine may be short of substances that keep crystals from sticking together and becoming stones. Kidney stones are also prone to develop in highly acidic or highly alkaline urine.
Problems in the way your system absorbs and eliminates calcium and other substances create the conditions for kidney stones to form. Sometimes, the underlying cause is an inherited metabolic disorder or kidney disease. Gout promotes specific types of kidney stones, as does inflammatory bowel disease. So do some drugs, including furosemide (Lasix), used in treating heart failure and high blood pressure; topiramate (Topamax), an anti-seizure drug; and indinavir (Crixivan), which is used to treat human immunodeficiency virus, the cause of AIDS.
Determining the type that makes up the bulk of the stone — usually a combination of calcium compounds — helps identify the underlying cause. The best preventive approach after your first kidney stone also depends partly on the stone’s composition.
If a stone stays inside one of your kidneys, it usually doesn’t cause a problem unless it becomes so large it blocks the flow of urine. This can cause pressure and pain, along with the risk of kidney damage, bleeding and infection. Smaller stones may partially block the thin tubes that connect each kidney to your bladder or the outlet from the bladder itself. These stones may cause ongoing urinary tract infections or kidney damage if left untreated.
Until a kidney stone moves into the ureter – the tube connecting the kidney and bladder, you may not know you have it. At that point, these signs and symptoms may occur:
- Pain in the side and back, below the ribs
- Fluctuations in pain intensity, with periods of pain lasting 20 to 60 minutes
- Pain waves radiating from the side and back to the lower abdomen and groin
- Bloody, cloudy or foul-smelling urine
- Pain on urination
- Nausea and vomiting
- Persistent urge to urinate
- Fever and chills if an infection is present
Kidney stones that don’t cause these symptoms may show up on X-rays when you seek medical care for other problems, such as blood in your urine or recurring urinary tract infections.
Many kidney stones go unnoticed until they cause acute symptoms — specifically, the pain of a stone going through your ureter. Sometimes, however, kidney stones are discovered in the course of looking for the cause of chronic urinary tract infections or blood in the urine.
If your doctor suspects you have kidney stones, you’re likely to have a blood analysis to look for excess calcium or uric acid and a 24-hour collection of urine to check whether you’re excreting too many stone-forming minerals or too few inhibiting substances.
You may also have one or more of the following imaging tests:
- Computerized tomography (CT) scan. This imaging test has become the standard of care for evaluating acute kidney stones. It’s rapidly performed, can identify stones regardless of composition and doesn’t require the use of contrast dye.
- Abdominal X-ray. An abdominal X-ray can visualize most kidney stones and can help to judge changes in the size of a stone over time.
- Ultrasound. Instead of X-rays, this diagnostic technique combines high-frequency radio waves and computer processing to view your internal organs. It’s safe, painless and noninvasive, but it may miss small stones, especially if they’re located in a ureter or your bladder.
- Intravenous pyelography (excretory urogram). This study can be useful in determining the location of stones in the urinary system and can define the degree of blockage caused by a stone. A contrast dye is injected into a vein in your arm and a series of X-rays is taken as the dye moves through your kidneys, ureters and bladder. This study has largely been replaced by the CT scan but is still useful in limited circumstances.
If you’re about to pass a stone, your doctor may ask you to urinate through a strainer so that the stone can be recovered and analyzed.
Treatment for kidney stones varies, depending on the type of stone and the cause. You may be able to move a stone through your urinary tract simply by drinking plenty of water — as much as 2 to 3 quarts (1.9 to 2.8 liters) a day — and by staying physically active.
Stones that can’t be treated with more-conservative measures — either because they’re too large to pass on their own or because they cause bleeding, kidney damage or ongoing urinary tract infections — may need professional treatment. Procedures include:
Extracorporeal shock wave lithotripsy (ESWL). This is a commonly used procedure for treating kidney stones. It uses shock waves to break the stones into tiny pieces that are then passed in your urine. In some cases, you may be partially submerged in a tub of water during the procedure. In others, you may lie on a soft cushion. You’ll generally require sedation or light anesthesia due to moderate pain caused by the shock waves. A loud noise is produced each time a shock wave is generated, and you’ll wear earphones to protect your hearing.
Your doctor will likely use X-rays or ultrasound to help determine the position of the stone as well as to monitor the status of the stone during treatment.
Complications that may occur with ESWL include blood in the urine, bruising on the back or abdomen, bleeding around the kidney and other adjacent organs, and discomfort as the stone fragments pass through the urinary tract. In addition, if the stone doesn’t shatter completely, you may need a second round of ESWL or ureteroscopic stone removal. After treatment, it may take months for all the stone fragments to pass.
Percutaneous nephrolithotomy. When ESWL isn’t effective, or the stone is very large, your surgeon may remove your kidney stone through a small incision in your back using an instrument called a nephroscope.
Ureteroscopic stone removal. This procedure may be used to remove a stone lodged in a ureter. The stone is snared with a small instrument (ureteroscope) that’s passed into the ureter through your bladder. Ultrasound or laser energy also can be directed through the scope to shatter the stone. These methods work especially well on stones in the lower part of the ureter.
Parathyroid surgery. Some calcium stones are caused by overactive parathyroid glands, which are located on the four corners of your thyroid gland, just below your Adam’s apple. When these glands produce too much parathyroid hormone, your body’s level of calcium can become too high, resulting in excessive excretion of calcium in your urine. Most often, this is the result of a small benign tumor in one of your four parathyroid glands. A doctor can surgically remove the tumor.
In many cases, you can prevent kidney stones by making a few lifestyle changes. For people with a history of kidney stones, doctors usually recommend passing at least 2.5 quarts (2.3 liters) of urine a day. To do this, you’ll need to drink about 14 cups (3.3 liters) of fluids every day — and even more if you live in a hot, dry climate. Water is best. Include a glass of lemonade every day, too. Make your own with real lemons, or use a liquid or frozen concentrate, but avoid powdered lemonade mixes.
In addition, if you tend to form calcium oxalate stones, your doctor may recommend restricting foods rich in oxalates. These include rhubarb, star fruit, beets, beet greens, collards, okra, refried beans, spinach, Swiss chard, sweet potatoes, sesame seeds, almonds and soy products. What’s more, studies show that an overall diet low in salt and very low in animal protein can greatly reduce your chance of developing kidney stones.
Medications can control the level of acidity or alkalinity in your urine and may be helpful in people who form certain kinds of stones. The type of medication your doctor prescribes will depend on the kind of kidney stones you have:
Calcium stones. To help prevent calcium stones from forming, your doctor may prescribe a thiazide diuretic or a phosphate-containing preparation. If you have calcium stones because of a condition known as renal tubular acidosis, your doctor may suggest taking sodium bicarbonate or potassium bicarbonate.
Uric acid stones. Your doctor may prescribe allopurinol (Zyloprim, Aloprim) to reduce uric acid levels in your blood and urine and a medicine to keep your urine alkaline. In some cases, allopurinol and an alkalinizing agent may dissolve the uric acid stones.
Cystine stones. Cystine stones are the hardest stones and the most difficult to treat. Your doctor may prescribe certain medications to alkalinize the urine or to bind the cystine in the urine in addition to recommending an extremely high urine output.