The National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC) reports that kidney stones are solid masses that form in the kidney out of substances that are normally present in urine. Small stones pass from the kidney to the bladder and out through the urethra without too much pain. Larger stones can cause an immense amount of pain. There are several different types of kidney stones.
Calcium Stones
Merck Manuals, an online medical library, reports that approximately 80 percent of all kidney stones are made of calcium, an essential nutrient. The NKUDIC adds that the calcium not absorbed by the bones and muscles is normally excreted from the kidneys into the urine. Most of the time the extra calcium travels from the kidneys, through the ureter (the tube that carries urine to the bladder), to the bladder and out through the urethra with no problem. However, sometimes the calcium precipitates out of the urine, and forms a stone that remains in the kidney. The stone may attract other waste products as well; the most common combination is calcium oxalate. According to the Mayo Clinic, people get oxalate from some fruits and vegetables, and also from nuts and chocolate. Certain factors can contribute to calcium kidney stones, such as intestinal bypass surgery and ingesting high levels of vitamin D.
Struvite Stones
According to the Mayo Clinic, struvite stones are kidney stones that develop as a result of an infection, such as a urinary tract infection. This type of kidney stone can grow quite quickly and become very large. Merck Manuals notes that struvite stones are made of a combination of magnesium, phosphate and ammonium. Another name for these stones are "infection stones," because they only form in response to an infection.
Uric Acid Stones
The Mayo Clinic reports that stones made of uric acid develop in people who are dehydrated, and who do not drink enough fluids. Uric acid stones also form in people whose diet is very high in protein, and in people who have gout, which is caused by elevated uric acid in the blood. The NKUDIC adds that people with recurring uric acid kidney stones may benefit from reducing the amount of meat they eat.
Cystine Stones
This type of kidney stone is very rare, according to the Mayo Clinic. Cystine kidney stones only affect people with a genetic disorder, called cystinuria, which induces the kidneys to release very high amounts of amino acids into the urine.
