Kidney Stone Classification
Urine has numerous waste products dissolved in it. At times, when the amount of liquid in the urine is less compared to the waste products, there is formation of crystals. These crystals tend to attract other elements which coalesce together to form a kidney stone. These kidney stones may either get flushed out of the body along with the urine or continue to increase in size until they are large enough to obstruct the normal flow of urine and produce symptoms like pain.
Every year, more than half a million people in America, visit the emergency room for kidney stones. Men have a 19% likelihood of developing a kidney stone in their lifetime while in women, this stands at around 9%.
Classification of kidney Stones
Let us look at the different types of kidney stones.
Most of the stones found in the kidneys are composed of calcium compounds, especially calcium oxalate and calcium phosphate. The frequency of prevalence of calcium stones is 70% to 80%. Some of the important causes behind the formation of calcium stones are:
- Hypercalciuria: This is the condition where there is increased amount of calcium in the urine. It may be because of increased intake of sodium and protein in the diet, increased amount of calcium in the blood (hypercalcemia), or because of chronic metabolic acidosis.
- Decreased Urinary Output: This is seen in warm weather conditions where there is increased water loss from the body. It is also seen in cases of chronic dehydration.
- Hyperuricosuria: This is seen in patients of gout or in people who consume a high protein diet.
- Hyperoxaluria: This can be genetic or in people who consume a low calcium high oxalate diet.
- Conditions with Low Urinary Citrate like chronic metabolic acidosis, renal tubular acidosis and inflammatory bowel disease.
- Idiopathic: In 25% cases, calcium stones form without any obvious reason.
Calcium oxalate stones are usually irregular in shape, like a mulberry. The irregular projections can cause bleeding due to damage to the kidney tissue. Because of the presence of blood on their surface, these stones appear dark in color. Calcium phosphate stones are smooth and round and appear dirty white to yellow in color.
Uric Acid Stones
These account for 10% to 15% of all kidney stones. They are seen when the pH of the urine is low i.e. it is acidic in nature, in patients suffering from chronic metabolic acidosis, in people with gout or those consuming a high protein diet, in obese people and those suffering from metabolic syndrome. Pure uric acid stones are radiolucent in nature. These stones are small and hexagonal in shape and yellow to reddish brown in color.
These are also called as infection stones as they are commonly associated with urinary tract infections. They are attributed to urea splitting bacteria encountered in UTIs. Women are more frequently affected. The frequency of these stones is around 10% to 15%. When these stones become too big, they are also called as stag-horn calculi.
These stones account for less than 1% of all kidney stones. They are caused due to high amount of cystine present in the urine. These stones are seen in people who suffer from autosomal recessive disorders of cystine, ornithine, arginine and lysine. They are also seen in people with renal tubular defect. These stones are radio-opaque because of the high sulfur content in them. They are hexagonal in shape and appear pink or yellow in color.
“Nephrolithiasis: Treatment, causes and prevention,” by Hall PM. Published in the Cleveland Clinical Journal of Medicine in 2009, accessed on May 20, 2014. Retrieved from: http://www.precisionnutrition.com/all-about-kidney-stones