Shedding Some Light on Kidney Stones

When most people hear of someone with a kidney stone, they often assume that every kidney stone is the same. While easy to assume, this is simply not true, and there are important distinctions to be made for different kinds of kidney stones. Each stone is formed from different kinds of materials, and therefore can be prevented with different diets or interventions. For example, with calcium oxalate stones, one might want to reduce oxalate in the diet. However, if the stone does not include oxalate, then this advice and change in diet would be unnecessary. In order to uncover what type of stone someone has, the type of stone can be determined by a doctor after it has been passed, or by identifying the chemicals in one’s blood or urine.

There are five more common kidney stones, starting with the most common; calcium oxalate.

Calcium oxalate stones are comprised of calcium oxalate, and there are two different forms of this type. Calcium oxalate monohydrate, and calcium oxalate dihydrate. Calcium oxalate monohydrate stones are harder and more resistant to fragmentation, and appear more often with higher levels of oxalate.

Calcium phosphate stones are the second most common stones, and is the bonding of calcium to phosphate instead of oxalate. There are also two different kinds of these stones, and they can form into either brushite or hydroxyapatite. Brushite is extra hard and resistant to shock treatments, while hydroxyapatite can actually plug the kidney tubules and injure kidney cells.

Uric acid kidney stones are about as common as calcium phosphate stones, but are different. Uric acid is a breakdown product of DNA and RNA, and forms when the urine is too acidic. The stones are red or orange, and can form rapidly. Uric acid does not have to bond with any other chemicals like calcium phosphate or oxalate, and therefore can form in seconds, but can also be passed quickly unless the stones are retained in the kidney. If so, they can grow to become quite large. However, since they are dependent on the acidity of the urine, they can be treated with alkali supplement. Occasionally though, uric acid stones might mix with calcium oxalate stones, which can be much more difficult to break up.

The second to last of the more common stones are struvite stones. These kidney stones are a combination of magnesium, ammonium, and phosphate, and cannot be made by the kidneys themselves. They are only able to exist because of the workings of bacteria. The soil bacteria from outside can find its way into our systems, bringing with it the ability to convert urea to ammonia, which then crystallizes with magnesium and phosphate, which are always found in urine. The stones can become large, and the bacteria can injure the kidneys, or enter the bloodstream and cause sepsis.

The last of these kidney stones are cystine stones, which are only formed in those with cystinuria; an inherited kidney disease. These stones come from cysteine, and grow to be extremely large, grow quickly, and can cause damage to the kidneys cells if not treated.

While these five are the main stones found in humans, there are a few kidney stones that are much more rare, and often are forms of mixed stones. As seen in the varying types of stones, there is much more to the condition than the broad terminology of a simple kidney stone.


1. Coe, F. Type of Kidney Stones – A Primer. Retrieved from URL:

2. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). (2013 November). Diet for Kidney Stone Prevention. Retrieved from URL: