Kidney stones (also known as renal calculi) are hard, mineral deposits that form in one or both kidneys; the stones are made up of compounds found in urine. Kidney stones vary in size, shape, and color. To be cleared from the body (or "passed"), the stones need to travel through ducts (ureters) that carry urine from the kidneys to the bladder to be excreted. Depending on their size, kidney stones can take days to weeks to pass out of the body.
Kidney stones can cause abdominal and back pain (renal colic). Renal colic can lead to nausea and vomiting. The site of pain can change as the stone moves through the urinary tract. Some small stones pass through the kidney and urinary tract with little discomfort, while larger ones can obstruct the flow of urine and impair kidney function. Kidney stones can also result in blood in the urine (hematuria) or infections in the kidney or urinary tract. Unusually larger stones or stones that are difficult to pass usually need to be medically removed.
Kidney stones can be classified by their composition. Up to 75 percent of all kidney stones are composed primarily of calcium. Stones can also be made up of uric acid (a normal waste product), cystine (a protein building block), or struvite (a phosphate mineral). Stones form when there is more of the concentrated substance in the urine than can be dissolved. This imbalance can occur when there is an increased amount of the substance in the urine, a reduced amount of liquid urine, or a combination of both.
Kidney stone disease is one of the most common urological conditions in the United States, and its incidence has increased over the past few decades secondary to dietary, climate, and behavioral influences. Some predisposing factors that have contributed to the rise in stone disease include increased salt consumption, increased consumption of animal protein, higher outdoor temperatures, and reduced fluid intake. Kidney stones are also associated with systemic diseases such as obesity, diabetes, and cardiac disease. Though up to 75 percent of all kidney stones are composed of calcium intake, increased dietary calcium intake has been associated with reduced risk of kidney stone. Supplemental calcium intake, on the other hand, has been associated with increased risk of stone formation.
It is estimated that about 10% of men and 7% women have a life time risk of developing a symptomatic kidney stone. People are most likely to develop kidney stones between the ages of 40 and 60, though kidney stones can appear at any age. It is very common for people who have one kidney stone to develop additional stones, usually within ten year of the first stone.
A CT scan is usually the preferred imaging study for diagnosing the presence of kidney stones. Once diagnosed, treatment is based on the type of stone and size. If the stone cannot be extracted or collected, urine studies can sometimes reveal composition of the kidney stone. Nephrologists can assist in tailoring a treatment plan to prevent future development of kidney stones based on stone composition. Urologists can assist with removal of large or obstructing stones.
If you are concerned that you have a history of recurrent kidney stones and would like to schedule a consultation to learn more about prevention, please call 817-233-6923.