What are kidney stones?
Kidney stones, or renal calculi, are solid masses made of crystals. Kidney stones usually originate in your kidneys. However, they can develop anywhere along your urinary tract, which consists of these parts:
Kidney stones are one of the most painful medical conditions. The causes of kidney stones vary according to the type of stone.
Not all kidney stones are made up of the same crystals. The different types of kidney stones include:
Calcium stones are the most common. They’re often made of calcium oxalate (though they can consist of calcium phosphate or maleate). Eating fewer oxalate-rich foods can reduce your risk of developing this type of stone. High-oxalate foods include:
- potato chips
However, even though some kidney stones are made of calcium, getting enough calcium in your diet can prevent stones from forming.
This type of stone develops when urine is too acidic. A diet rich in purines can increase urine’s acidic level. Purine is a colorless substance in animal proteins, such as fish, shellfish, and meats.
This type of stone is found mostly in women with urinary tract infections (UTIs). These stones can be large and cause urinary obstruction. They result from a kidney infection. Treating an underlying infection can prevent the development of struvite stones.
Cystine stones are rare. They occur in both men and women who have the genetic disorder cystinuria. With this type of stone, cystine — an acid that occurs naturally in the body — leaks from the kidneys into the urine.
The greatest risk factor for kidney stones is making less than 1 liter of urine per day. This is why kidney stones are common in premature infants who have kidney problems. However, kidney stones are most likely to occur in people between the ages of 20 and 50.
Different factors can increase your risk of developing a stone. In the United States, white people are more likely to have kidney stones than black people.
Sex also plays a role. More men than women develop kidney stones, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
A history of kidney stones can increase your risk. So does a family history of kidney stones.
Other risk factors include:
Kidney stones are known to cause severe pain. Symptoms of kidney stones may not occur until the stone begins to move down the ureters. This severe pain is called renal colic. You may have pain on one side of your back or abdomen.
In men, pain may radiate to the groin area. The pain of renal colic comes and goes, but can be intense. People with renal colic tend to be restless.
Other symptoms of kidney stones can include:
- blood in the urine (red, pink, or brown urine)
- discolored or foul-smelling urine
- frequent need to urinate
- urinating small amounts of urine
In the case of a small kidney stone, you may not have any pain or symptoms as the stone passes through your urinary tract.
Stones don’t always stay in the kidney. Sometimes they pass from the kidney into the ureters. Ureters are small and delicate, and the stones may be too large to pass smoothly down the ureter to the bladder.
Passage of stones down the ureter can cause spasms and irritation of the ureters. This causes blood to appear in the urine.
Diagnosis of kidney stones requires a complete health history assessment and a physical exam. Other tests include:
- blood tests for calcium, phosphorus, uric acid, and electrolytes
- blood urea nitrogen (BUN) and creatinine to assess kidney functioning
- urinalysis to check for crystals, bacteria, blood, and white cells
- examination of passed stones to determine their type
The following tests can rule out obstruction:
- abdominal X-rays
- intravenous pyelogram (IVP)
- retrograde pyelogram
- ultrasound of the kidney (the preferred test)
- MRI scan of the abdomen and kidneys
- abdominal CT scan
The contrast dye used in the CT scan and the IVP can affect kidney function. However, in people with normal kidney function, this isn’t a concern.
There are some medications that can increase the potential for kidney damage in conjunction with the dye. Make sure your radiologist knows about any medications you’re taking.
Treatment is tailored according to the type of stone. Urine can be strained and stones collected for evaluation.
Drinking six to eight glasses of water a day increases urine flow. People who are dehydrated or have severe nausea and vomiting may need intravenous fluids.
Other treatment options include:
Pain relief may require narcotic medications. The presence of infection requires treatment with antibiotics. Other medications include:
- allopurinol (Zyloprim) for uric acid stones
- thiazide diuretics to prevent calcium stones from forming
- sodium bicarbonate or sodium citrate to make the urine less acidic
- phosphorus solutions to prevent calcium stones from forming
- ibuprofen (Advil) for pain
- acetaminophen (Tylenol) for pain
- naproxen sodium (Aleve) for pain
Extracorporeal shock wave lithotripsy uses sound waves to break up large stones so they can more easily pass down the ureters into your bladder. This procedure can be uncomfortable and may require light anesthesia. It can cause bruising on the abdomen and back and bleeding around the kidney and nearby organs.
Tunnel surgery (percutaneous nephrolithotomy)
A surgeon removes the stones through a small incision in your back. A person may need this procedure when:
- the stone causes obstruction and infection or is damaging the kidneys
- the stone has grown too large to pass
- pain can’t be managed
When a stone is stuck in the ureter or bladder, your doctor may use an instrument called a ureteroscope to remove it.
A small wire with a camera attached is inserted into the urethra and passed into the bladder. The doctor then uses a small cage to snag the stone and remove it. The stone is then sent to the laboratory for analysis.
Proper hydration is a key preventive measure. The Mayo Clinic recommends drinking enough water to pass about 2.6 quarts of urine each day. Increasing the amount of urine you pass helps flush the kidneys.
You can substitute ginger ale, lemon-lime soda, and fruit juice for water to help you increase your fluid intake. If the stones are related to low citrate levels, citrate juices could help prevent the formation of stones.
Eating oxalate-rich foods in moderation and reducing your intake of salt and animal proteins can also lower your risk of kidney stones.
Your doctor may prescribe medications to help prevent the formation of calcium and uric acid stones. If you’ve had a kidney stone or you’re at risk for a kidney stone, speak with your doctor and discuss the best methods of prevention.