Kidney Stones - Complications

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• Too much uric acid in the urine for a long period of time (the most important cause of uric acid stones)
• Lower-than-normal amounts of urine produced
• Hyperuricosuria, a metabolic disorder that leads to high levels of uric acid in the urine

Note: Hyperuricosuria can also trigger calcium stones. Therefore, patients with hyperuricosuria may have a combination of calcium and uric acid stones.

A number of conditions and other factors may contribute to, or cause, uric acid stones:

• Gout: Uric acid and other kidney stones develop in up to 25% of patients with primary gout, a painful form of arthritis that occurs when uric acid in the blood forms crystals in one or more joints.
• Diabetes: People with type 2 diabetes have highly acidic urine that can lead to kidney stones, particularly uric acid stones.
• Insulin resistance: People with insulin resistance have an increased risk for uric acid stones. The reason is unknown, but it may be related to the transport of certain salts through the kidneys. This transport changes in patients with insulin resistance.
• Kidney abnormalities: Kidney problems that reduce the production of ammonia, particularly in people with diabetes or insulin resistance, may lead to the formation of uric acid stones.
• Genetic factors: Inherited factors can increase a person's risk for uric acid stones.
• Hypocitraturia: Hypocitraturia is a low amount of citrate in the urine.
• Diet: Eating too much animal protein increases the risk of forming uric acid stones.

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Other risk factors include:

• Certain medications (chemotherapy drugs, diuretics, and salicylates)
• Binge drinking
• Not eating for long periods of time (fasting)
• Lead poisoning
• Treatment of blood cancers (leukemia, multiple myeloma, and lymphomas)
• Some rare types of anemia (low levels of red blood cells in the blood)
• Chronic diarrhea

Causes of Struvite Stones

Struvite stones are almost always caused by urinary tract infections. Bacteria produce certain enzymes, which raise the concentration of ammonia in the urine. Ammonia makes up the crystals that form struvite stones. The stone-promoting bacteria are usually Proteus, but may also include Pseudomonas, Klebsiella, Providencia, Serratia, and Staphylococcus. Women are twice as likely to have struvite stones as men.

Causes of Other Stones

Other stones, including cystine and xanthine stones, are usually due to genetic abnormalities.

Causes of Cystine Stones. Cystine stones develop from genetic defects that cause the abnormal transport of amino acids in the kidney and gastrointestinal system, leading to a build-up of cystine. Researchers have identified two genes responsible for this condition: SLC3A1 and CLC7A9.

Causes of Xanthine Stones. In some cases, xanthine stones may develop in patients being treated with allopurinol for gout.

Review Date: 06/08/2010
Reviewed By: Reviewed by: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).