Passing Kidney Stones

Kidney stones are actually crystals of different shapes, sizes and chemistry, made from salts excreted in urine. During certain favorable conditions, these urinary salts may come out of solution, and deposit anywhere along the urinary tract. Ordinarily, we would be unaware of these salts in the urine, but as they form crystals within the urinary tract, larger aggregates could result that may create new clinical problems. Those problems include obstruction of the ureter (drainage tract) or bleeding within the urinary tract.

Any urinary salt can potentially come out of solution, and form a kidney stone. However, the commonly found stones are made of calcium, either as calcium oxalate or calcium phosphate. Less commonly, stones may be made up of uric acid, struvite (often in deep-seated kidney infections) or cystine (in rare inherited diseases associated with poor handling of cystine metabolism).

When evaluating kidney stones, it is crucial to uncover what risk factors might trigger the formation of such stones. Commonly found risk factors include:
v Insufficient amounts of drinking water
v Urinary tract infections
v Excessive calcium excretion in urine
v Drug interactions
v History of gout
v Family history of kidney stones
v Excessive salt intake (excessive salt intake leads to excessive salt excretion, which in turn triggers excess calcium excretion in urine)
v Excessive meat intake (leads to excess uric acid synthesis)

When a kidney stone is diagnosed, it is important to retrieve the stone, and correctly analyze its chemical composition in order to determine the risks of recurrence, and how best to avoid this. Most stones will pass spontaneously with no help. If the stone is not passed, and there is a risk of kidney damage, it might be necessary to remove the stone surgically. Alternatively, ultrasonic shock waves may be directed at breaking up the larger stone fragments, or a special instrument inserted through a tiny incision made at the flank (percutaneous nephrolithotomy) or threaded carefully through the urethra (endoscopic urethrolithotomy).

For patients forming calcium oxalate stones, it is crucial to limit the dietary intake of oxalate-rich foods. Those include all soy products, nuts (peanuts & pecans), chocolate/cocoa products, wheat germ, beets, collards, okra, pokeweed, spinach, rhubarb, pursiane leaves, black pepper and teas (though green tea is OK). For those forming uric acid stones, restrict dietary protein to under 12 ounces of meat. For all who are at risk of passing stones of any type, drink more water. If you do not get up once or twice each night to urinate, you are probably not drinking nearly enough!

It is worth remembering that kidney stones are common, painful and treatable. You are not alone! In the United States, it is estimated that about 10% of people will suffer at least 1 kidney stone attack during their life. Most stones, at least 80%, contain calcium salts, usually as calcium oxalate or calcium phosphate.

For anyone to form a kidney stone, the urine has to be “supersaturated” with a chemical substance, which may eventually come out of (urine) solution as a “crystal” (solid). Urine flow can be visualized as a perpetual battle between agents that cause stone formation and those that inhibit it. Indeed, any large particle such as cell debris or a foreign body may act as the “trigger” for further crystal formation from supersaturated urine, a process referred to as “nucleation”. The “nucleus” creates the “scaffold” for more salts to come out of solution. Often, this process starts deep within the kidney tissue (interstitium) surrounding the thin limb of Henle’s loop. Once crystal “debris” forms within kidney tissue, the stage is set for more salts to come out of solution from the supersaturated urine, until the mass is large enough to erode into the urinary collecting tract as “Randall’s plaque”. Within the urinary tract, further stone growth continues until urinary flow is impeded, setting the stage for clinical symptoms and kidney damage.
Commonly, the original trigger for stone formation is chemically different from the salts that later aggregate to complete the stone mass; this process is called “heterogenous nucleation”, where the core of the stone is different from the salts deposited around that central core.

A patient has to increase his army of kidney stone “inhibitors” within the urinary tract, or decrease the supersaturation of the urine. To help guide treatment, it is helpful to analyze the character of the stone, as well as measure the amount of “stone inhibitors” in the urine. Few patients are prone to kidney stones either because of other diseases enabling very high calcium levels (such as sarcoidosis), or an excess of urinary acidity (as in renal tubular acidosis).

Again, the good news is this: you can prevent kidney stones! To prevent kidney stone formation, closely follow the guidelines below:
q Increase urine volume to 2.5 liters, which means drinking at least 3.3 liters of fluid (or even higher during hot weather or work outdoors). This is the single most important step to avoid forming new stones. All fluids count, but water is best; grapefruit juice should be avoided. Spread out the water as much as possible, and don’t forget to drink at night. If you are not waking up once or twice to urinate at night, you probably are not drinking enough!
q Reduce dietary oxalate intake, as this is a common component of calcium-containing stones. Those foods rich in oxalate include wheat germ, okra, pokeweed, soy foods, spinach, rhubarb, lime/lemon, orange peel, tea (green tea is OK), black pepper, figs, Swiss chard, nuts, sorrel, beets, cocoa, chocolate, blackberries, blueberries, lamb quarters.
q Reduce dietary salt intake: urinary excretion of sodium (in cooking salt) is excreted in parallel with calcium. The more sodium is ingested (and excreted), the more calcium is also excreted. Cut down salt intake to under 2 grams daily.
q Reduce urinary acid load: this generally comes from animal meat, but may also occur in various conditions such as chronic diarrhea and diabetes mellitus. Excess animal protein leads to excess uric acid formation. Limit dietary meat intake to under 12 ounces a day, which is enough for an adult.
q Increase urinary citrate: the most effective method is using oral Urocit-K given by mouth TID.
q Decrease urinary calcium: this is best achieved by cutting off calcium passage into the urine, not by reducing the much-needed calcium in the diet. Your bones do need calcium, but the challenge is to ensure extra calcium does not “leak” into the urine. This is best achieved with oral Chlorthalidone or other mild diuretic drug, but not Lasix.
q Avoid the temptation to restrict dietary calcium: we now know that paradoxically, limiting dietary calcium only increases oxalate absorbtion, and actually increases stone risk (Borhi et al, N England J Medicine 2002)!

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  • Date Posted:
    Sunday, February 1