Kidney Stones – causes and diagnosis
What causes kidney stones?
Kidney stones can form when substances in the urine—such as calcium, oxalate, and phosphorus—become highly concentrated. Certain foods may promote stone formation in people who are susceptible, but scientists do not believe that eating any specific food causes stones to form in people who are not susceptible. People who do not drink enough fluids may also be at higher risk, as their urine is more concentrated.
People who are at increased risk of kidney stones are those with
- hypercalciuria, a condition that runs in families in which urine contains unusually large amounts of calcium; this is the most common condition found in those who form calcium stones
- a family history of kidney stones
- cystic kidney diseases, which are disorders that cause fluid-filled sacs to form on the kidneys
- hyperparathyroidism, a condition in which the parathyroid glands, which are four pea-sized glands located in the neck, release too much hormone, causing extra calcium in the blood
- renal tubular acidosis, a disease that occurs when the kidneys fail to excrete acids into the urine, which causes a person’s blood to remain too acidic
- cystinuria, a condition in which urine contains high levels of the amino acid cystine
- hyperoxaluria, a condition in which urine contains unusually large amounts of oxalate
- hyperuricosuria, a disorder of uric acid metabolism
- gout, a disorder that causes painful swelling of the joints
- blockage of the urinary tract
- chronic inflammation of the bowel
- a history of gastrointestinal (GI) tract surgery
Others at increased risk of kidney stones are people taking certain medications including
- diuretics—medications that help the kidneys remove fluid from the body
- calcium-based antacids
- the protease inhibitor indinavir (Crixivan), a medication used to treat HIV infection
- the anti-seizure medication topiramate (Topamax)
What are the types of kidney stones?
Four major types of kidney stones can form:
- Calcium stones are the most common type of kidney stone and occur in two major forms: calcium oxalate and calcium phosphate. Calcium oxalate stones are more common. Calcium oxalate stone formation may be caused by high calcium and high oxalate excretion. Calcium phosphate stones are caused by the combination of high urine calcium and alkaline urine, meaning the urine has a high pH.
- Uric acid stones form when the urine is persistently acidic. A diet rich in purines—substances found in animal protein such as meats, fish, and shellfish—may increase uric acid in urine. If uric acid becomes concentrated in the urine, it can settle and form a stone by itself or along with calcium.
- Struvite stones result from kidney infections. Eliminating infected stones from the urinary tract and staying infection-free can prevent more struvite stones.
- Cystine stones result from a genetic disorder that causes cystine to leak through the kidneys and into the urine, forming crystals that tend to accumulate into stones.
What are the symptoms of kidney stones?
People with kidney stones may have pain while urinating, see blood in the urine, or feel a sharp pain in the back or lower abdomen. The pain may last for a short or long time. People may experience nausea and vomiting with the pain. However, people who have small stones that pass easily through the urinary tract may not have symptoms at all.
How are kidney stones diagnosed?
To diagnose kidney stones, the health care provider will perform a physical exam and take a medical history. The medical history may include questions about family history of kidney stones, diet, GI problems, and other diseases and disorders. The health care provider may perform urine, blood, and imaging tests, such as an x ray or computerized tomography (CT) scan to complete the diagnosis.
- Urinalysis. Urinalysis is testing of a urine sample. The urine sample is collected in a special container in a health care provider’s office or commercial facility and can be tested in the same location or sent to a lab for analysis. Urinalysis can show whether the person has an infection or the urine contains substances that form stones.
- 24 hour urine collections. You may be asked to provide 2 (24hr) urine samples to check the urine for substances such as calcium, urate, cysteine etc to aid the clinician in trying to identify potential causes for stone formation.
- Blood test. A blood test involves may be performed. The blood test can show biochemical problems that can lead to kidney stones.
- Abdominal x ray. An abdominal x ray is a picture created using radiation and recorded on film or on a computer. The amount of radiation used is small. An x ray is performed at a hospital or outpatient center by an x-ray technician, and the images are interpreted by a radiologist—a doctor who specializes in medical imaging. Anesthesia is not needed. The person will lie on a table or stand during the x ray. The x-ray machine is positioned over the abdominal area. The person will hold his or her breath as the picture is taken so that the picture will not be blurry. The person may be asked to change position for additional pictures. The x rays can show the location of stones in the kidney or urinary tract.
- CT scans. CT scans use a combination of x rays and computer technology to create three-dimensional (3-D) images. A CT scan may include the injection of a special dye, called contrast medium. CT scans require the person to lie on a table that slides into a tunnel-shaped device where the x rays are taken. The procedure is performed in an outpatient center or hospital by an x-ray technician, and the images are interpreted by a radiologist. Anesthesia is not needed. CT scans can show stone locations and conditions that may have caused the stone to form.
Information reproduced from NIDDK website.
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