What are stones and the difference between kidney stones and ureteral stones?
Stones formed in the kidney are called kidney stones. Ureteral stone is a kidney stone that has left the kidney and moved down into the ureter.
Kidney stones (calculi) are hardened mineral deposits that form in the kidney. They originate as microscopic particles or crystals and develop into stones over time. The medical term for this condition is nephrolithiasis, or renal stone disease.
The kidneys filter waste products from the blood and add them to the urine that the kidneys produce. When waste materials in the urine do not dissolve completely, crystals and kidney stones may form.
Stones may pass out of the kidney, become lodged in the tube that carries urine from the kidney to the bladder (ureter), and cause severe, excruciating pain that begins in the lower back and radiates to the groin. A lodged stone can block the flow of urine, causing pressure to build in the affected ureter and kidney. Increased pressure results in stretching and spasm, which cause the severe pain.
Kidney Stone Formation
Kidney stones form when there are too many chemicals to easily dissolve in the available urine. The most common causes of this are:
- a high level of urinary calcium (hypercalciuria),
- high urinary oxalate (hyperoxaluria),
- high urinary uric acid (hyperuricosuria),
- insufficient urinary citrate, or
- inadequate water flowing through the kidneys.
The kidneys must maintain an adequate amount of water in the urine to dissolve all the removed waste products. If dehydration occurs, high levels of substances that do not dissolve completely (e.g., calcium, oxalate, uric acid) may form crystals that slowly build up into kidney stones.
Urine normally contains chemicals—citrate, magnesium, pyrophosphate—that help prevent the formation of crystals and stones. Low levels of these inhibitors can contribute to the formation of kidney stones. Of these, citrate is the most important.
Kidney stones are most prevalent in patients between the ages of 30 and 45, with men affected three times more often than women. Overall incidence declines after age 50.
Small, smooth kidney stones may remain in the kidney or pass without causing pain (called “silent” stones). Stones that lodge in the tube that carries urine from the kidneys to the bladder (ureter) cause the urinary system to spasm and produce pain. The pain is unrelated to the size of the stone and often radiates from the lower back to the side or groin.
A “small” stone (usually 4 mm in diameter or less) has a 90% chance of spontaneous passage. Stones that are 8 mm in diameter or larger usually require medical intervention.
Other symptoms of kidney stones may include the following:
- Blood in the urine (hematuria)
- Increased frequency of urination (urinary urgency)
- Nausea and vomiting
- Pain during urination (stinging, burning)
- Tenderness in the abdomen and kidney region
- Urinary tract infection (UTI; fever, chills, loss of appetite)
Kidney stone complications include kidney damage and scarring, decreased kidney function, obstruction of the ureter, recurrent stones and infections, and renal colic (severe pain that radiates from the kidney region to the abdomen and groin).
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Kidney stone treatment depends on the size and type of stone, the underlying cause, the presence of any urinary infection, and whether the condition recurs. Stones 4 mm and smaller (less than 1/4 inch in diameter) pass without intervention in 90% of cases; those 5–7 mm do so in 50% of cases; and those larger than 7 mm rarely pass without a surgical procedure. Patients are advised to avoid becoming too sedentary, because physical activity, especially walking, can help move a stone.
Medications called alpha blockers have been shown to increase the spontaneous passage of kidney stones, especially smaller stones in the lower ureter near the bladder. These medications have the ability to relax the muscle tension inside the ureter. This relaxation serves to improve spontaneous stone passage rates by about 30%.
If possible, the kidney stone is allowed to pass naturally and is collected for analysis. The patient is instructed to strain their urine to obtain the stone(s) for analysis. It is important to analyze the chemical composition of kidney stones to help determine how to prevent recurrent stone formation. The urine may be strained using an aquarium net or another device. Each voiding should be strained until the physician instructs the patient otherwise.
Dietary changes may be required and fluid intake should be increased. Patients with stones must increase their urinary output. Generally, 2000 cc of urine per day (slightly more than 1/2 gallon) is recommended and patients should drink enough water to produce this amount of urine daily. In some cases (e.g., some cystine stone formers), even higher levels of fluid intake are required.