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.
Types of kidney stones
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 kidney stone is more common in men than in women. They can occur in people with gout or those going through chemotherapy. 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.
Risk factors for kidney stones
The greatest risk factor for kidney stones is making less than one 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. Typically, Caucasians are more likely to have kidney stones than those of African descent.
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:
- a diet with high levels of protein, salt, or glucose
- hyperparathyroid condition
- gastric bypass surgery
- inflammatory bowel diseases that increase calcium absorption
- taking medications such as diuretics, antiseizure drugs, and calcium-based antacids
Recognizing the symptoms and signs of a kidney stone
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.
Why kidney stones can be a problem
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 as they pass. This causes blood to appear in the urine.
Sometimes stones block the flow of urine. This is called a urinary obstruction. Urinary obstructions can lead to kidney infection and kidney damage.
Testing for and diagnosing kidney stones
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 study)
- 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.