Image obtained from (Tanner, 2009).

Nephrolithiasis, which is the development of kidney stones, affects 5-15% of the population worldwide (Moe, 2006). Kidney stones can affect any part of the urinary tract, from the kidneys to the ureter. Passing kidney stones can be very painful, however kidney stones typically do not cause permanent damage (Mayo Clinic, 2012). Kidney stones tend to form when there are excessive amounts of relatively insoluble salts in the filtrate, or when insufficient fluid intake creates highly concentrated filtrate. This filtrate will eventually form a solid mass called a kidney stone (VanMeter, 2013).

In most texts I read all three of these terms were used to refer to a kidney (urinary) stone or the formation of a kidney stone.

Definitions obtained from (VanMeter, 2013)

Nonobstructing stones initially produce no symptoms or signs apart from hematuria (blood in urine). Stone passage produces renal colic that usually begins as a mild discomfort and progresses to a plateau of severity for about an hour. If the stone obstructs the uretero-pelvic junction, pain will localize; as the stone moves down the ureter, pain moves with it (Coe, 2005). Other symptoms include pain when urinating, red or brown urine, cloudy urine, persistent urge to urinate, more frequent urination, and nausea or vomiting. Often kidney stones do not display symptoms until they begin to move within the kidneys or ureter. Pain will often shift or alter in intensity as the stone moves through the urinary tract (Mayo Clinic, 2012).

Often kidney stones will pass on their own, and therefore do not require immediate medical attention. Stone size influences the rate of spontaneous stone passage. For example, up to 98% of small stones (less than 5 mm diameter) may pass spontaneously through urination within four weeks of the onset of symptoms, however for larger stones (5-7mm) this rate decreases to about 50%, and stones larger than 7mm typically always require surgical intervention (Miller, 2007). However, when severe symptoms occur a doctor should be seen right away. These symptoms could indicate a blockage that is preventing urine from passing and a fever or chills could indicate the presence of an infection.

There is no single cause of kidney stones; different types have different causes. In fact, many kidney stones are the results of a different underlying disease or condition (Moe, 2011). Kidney stones form when urine contains more crystal-forming substances, like calcium or oxalate, than the fluid can dilute (Mayo Clinic, 2012).

Image obtained from (Miller, 2007).

Calcium stones are by far the most common nephroliths, accounting for more than 75%
of stones. Uric acid stones represent about 5–10%,
trailed by struvite, then cystine stones (Moe, 2006). Calcium kidney stones form when calcium levels in the urine are high owing to hypercalcemia, they form even more readily when the pH of the urine is alkaline (VanMeter, 2013). Calcium stones are most commonly formed from calcium oxalate, but can also be formed by calcium phosphate or carbonate. Oxalate occurs naturally in foods like spinach, fruits, and nuts, and it is produced by the liver (Mayo Clinic, 2012). A vegetarian diet is high in oxalates, leading to increased risk of calcium stone formation. Uric acid stones develop in people with hyperuricemia (could be due to high-purine diet or gout) and develop more readily when urine pH is acidic (VanMeter, 2013). Uric acid stones are particularly associated with metabolic disorders like obesity. Struvite kidney stones generally form in response to an infection like a UTI. These can form rapidly with few initial symptoms. Cystine kidney stones are very rare, only about 1% of kidney stones. They form in people with a rare hereditary disorder that allows the amino acid cystine to leak from the kidneys into the urine to form crystals (Coe, 2006). Other types of kidney stones can occur, however they are extremely rare.

Kidney stones affect all geographical, cultural, and racial groups. The lifetime risk of developing a kidney stone is 12- 16%, however the recurrence rates approach 50%, meaning the once you develop a kidney stone you are far more likely to develop a second one (Teichman, 2004). Kidney stones are far more common in men (about 80% of all stones occur in men), and they are more common in people over 40 years of age (Coe, 2005). Dehydration is also a major risk factor; inadequate intake or the rapid loss of fluids leaves urine too concentrated, there is not enough fluid to dissolve crystal-forming substances, and thus stones will form (Mayo Clinic, 2012). The risk factors for developing a kidney stone does vary depending on the type of kidney stone.

Certain dietary factors, metabolic disorders, and digestive surgeries will all increase calcium or oxalate concentration in urine which will increase the risk of calcium kidney stones. High doses of calcium, excess vitamin D, and hyperparathyroidism all can lead to hypercalcemia, which will increase the concentration of calcium excreted in urine (Coe, 2005). Increased sodium or oxalate consumption has also been found to increase the risk of stone formation. Gastric bypass surgery or Irritable Bowel Syndrome can affect your absorption of calcium and water, thus increasing the concentration of stone-forming solutes in the urine (Mayo Clinic, 2012). Certain genetic disorders do play a role in increases the occurrence of calcium stones, however most disorders are extremely rare. For example, Dent disease is a rare X-linked disorder that causes stone formation due to a genetic mutation altering chloride ion channels, and causing hypercalcemia. Bartter syndrome (5 variations) is another genetic disorder that causes defects in calcium resorption and leads to hypercalciuria (Coe, 2005).

Gout, a high purine diet, or cancer chemotherapy all increase uric acid concentration in urine, making stone development a greater risk (VanMeter, 2013). High protein diets are essentially high-protein diets, when purines are broken down in the body they form uric acid. Urine pH is also a major factor in the formation of uric acid stones, which requires an acidic pH. Urine pH falls with increasing body weight, probably due to insulin resistance. Therefore, a low urine pH and uric acid stones are common in people with gout, diabetes mellitus, obesity, and other metabolic syndromes (Coe, 2005)

Unlike the other types of kidney stones, struvite stones occur more commonly in women. The formation is associated with bacterial urinary infections like a urinary tract infection (Mayo Clinic, 2012). Any history of urinary infections would increase the risk of struvite kidney stones.

Cystine kidney stones are the result of a rare genetic disorder: cystinuria. Cystinuria is characterized by genetic mutations in renal epithelial cell transporters resulting in the reduced reabsorption and increased urine excretion of certain amino acids, including cystine. This leads to cystine supersaturation in the urine due to overexcretion thus causing the formation of cystine kidney stones (Coe, 2005).