What causes kidney stones?

Kidney stones form when the urine has too many crystal-forming chemicals and/or not enough substances that protect against crystal formation. If the crystals do not rapidly pass through the urinary tract, they can grow and form stones. When the volume is too low, stone forming materials become concentrated helping to promote stone growth.

What did I do to cause my stones?

Genetics, diet, fluid intake, work environment, geographical location and certain medical conditions are all factors which may influence the formation of stones.

What exactly are kidney stones?

Kidney stones are hard objects made of a solid crystalline material imbedded in proteins usually present in urine. Most stones form on the interior surfaces of the kidney at the site where the final urine leaves the kidney tissue and enters the hollow collecting system that will take it down to the bladder. Because they form on the kidney surface, stones are often without symptoms and are found by x-ray undertaken to determine unexplained blood in the urine. Though anchored to the kidney, these hard objects can cause local injury and bleeding that doctors detect with routine urinalysis.

When a stone breaks loose from the place where it is formed, it falls into the urine collecting system and may attempt to pass through the bladder. Small stones, less than 5.0 mm in size, usually pass through. Those above 6.0 mm usually do not. Either way, a stone that attempts to pass can produce extreme pain, bleeding, and obstruction of the kidney from which it is passing. The pain is what most often signals stone disease to a patient.

The kind of material of which the stone is made determines an important part of the diagnosis and treatment. Therefore, all stones should be collected and analyzed whenever possible.

Curious about the different types of kidney stones?

Calcium Oxalate Stones
The most common kidney stone is made of calcium oxalate. Calcium is a main constituent of bone and is always present in blood and urine. Oxalate is a by-product of metabolism and is also present in many foods. When they combine in the kidneys, calcium and oxalate produce a very insoluble salt that easily forms a solid stone. Once they form, these stones can never dissolve and must be passed or broken up by a surgeon using modern technologies.

Calcium Phosphate Stones
Less common are calcium phosphate stones. Calcium phosphate crystals are the stiffener that makes bone rigid. Large amounts of phosphate from food are eliminated in the urine of normal people every day. The usual cause of calcium phosphate stones is a disease that increases urine calcium and also makes the urine abnormally alkaline. When the urine is not alkaline, high urine calcium concentrations produce mainly calcium oxalate stones, but when the urine is alkaline, calcium is bound by urine phosphorus, and calcium phosphate stones are produced. Minor amounts of calcium phosphate are usual in calcium oxalate stones and have no clinical significance. When the bulk of the stone (more than half) is calcium phosphate, special treatment is often needed.

Uric Acid Stones
Also less common but very important are stones made of uric acid. These can either be pure uric acid or a mixture of uric acid with calcium oxalate. Uric acid is a breakdown product of DNA and RNA and crystallizes into stones whenever the urine is chronically acid in character. Uric acid stones can dissolve if the urine can be made to be less acid. Causes of abnormally acidic urine include heredity, gout, renal disease, and intestinal disease, as well as dietary extremes.

Struvite Stones
Stones composed of struvite (magnesium, ammonium, and phosphate) are always produced by infection. Some bacteria that infect the kidneys and urinary tract can break down urea, a universal constituent of urine, to ammonia. The ammonia makes the urine in the vicinity of the bacteria extremely alkaline, and the normal amounts of magnesium and phosphorus present in all urine form crystals with dissolved ammonia and make this large type of stone. Unlike calcium oxalate and most calcium phosphate stones, struvite stones can rapidly grow so large as to fill the entire interior of the kidney drainage system. There are two types of struvite stone-forming patients, and they require completely different treatments.

Cystine Stones
This uncommon stone is made of the amino acid cystine and occurs only in patients who have an inherited disease called cystinuria. Urine can dissolve no more than 300 mg of cystine in a liter, and normal people lose less than 100 mg daily in their urine. Cystine is present in blood and filtered from blood by the kidney in very large amounts. People with cystinuria lack the renal mechanisms to reclaim the filtered cystine back into the blood. This valuable nutrient is lost in the urine and makes large and potentially dangerous stones, often beginning in infancy or childhood.

Unusual Stones
Certain antiviral drugs, as well as triamterene (a diuretic) are well known to cause kidney stone formation. Hydroxyadenine stones form in people who have a very rare inherited enzyme deficiency that causes over production of the material.