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Stone Disease - Frequently Asked Questions

Overview | Diagnosis | Treatment | FAQ

Can I pass the stone?

The ureter moves stones along by rhythmic contractions that begin as the ureter leaves the kidney and continue to the level of the bladder. These contractions occur every 12 seconds or so. Stones usually get hung up in one of three places: at the UPJ (ureteral pelvic junction - where the ureter meets the renal pelvis); about two-thirds of the way down the ureter, where it crosses the iliac vessels; and at the UVJ (ureteral vesicle [another name for bladder] junction – where the ureter penetrates the muscular wall of the bladder).

The odds of passing a stone are 90% for a stone less than 4mm, 50% for a stone 4-6mm, and 20% or less for a stone larger than 6mm.

The time it takes to pass a stone varies; it can take days, weeks, or even months. Reasons for intervening include pain unrelieved by medication, urinary tract infection complicated by an obstructing stone, a solitary kidney, or a high-grade obstruction (almost complete or complete obstruction).

If a stone gets stuck during its journey down the ureter, it can cause an incomplete or complete obstruction. If urine can still sneak by, it’s called an incomplete obstruction. On the other hand, if the passage of urine is completely blocked, it’s called a complete obstruction. A complete obstruction can cause residual renal damage if it’s not relieved in a timely manner (within a few weeks or so). The longer the obstruction persists, the greater the risk of permanent renal damage.

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How can I prevent kidney stones?

Recurrent stone formation can be prevented 80% of the time. Although medication is occasionally required, natural remedies are sufficient in most situations. A book by John S. Rodman, Cynthia Seidman, and Rory Jones called No More Kidney Stones (NY: John Wiley & Sons, Inc., 1996) is a good resource for preventive strategies. The following three factors are an integral part of every successful stone prevention program:

Risk factors: The first step is to identify any known risk factors. Click here for the list.

Tests: The second step is to decide whether more extensive testing is required. Everybody should have a routine urinalysis (microscopic evaluation of the urine). Additional work up is indicated for people with a current or past history of multiple stones, unusual stones (e.g., cysteine), or stones that are continuing to grow in size deserve further work-up. For more detailed information on diagnosis, click here. This work-up consists of the following:

1. Questions regarding a family and personal history of stones

2. Underlying medical conditions (for instance, a history of Chron’s disease, intestinal bypass surgery, constipation, medications, etc.)

3. Dietary habits

4. Occupation

5. Leisure activity

6. Stone analysis

7. X-ray studies

8. Selected blood studies

9. Metabolic tests on two twenty-four hour urine collections

Treatment Plan: The third step is to formulate a tailored treatment plan, click here for more details. Every treatment plan should include dietary and lifestyle modifications that minimize risk factors picked up on history and testing. Medication may also be required in some situations, depending on the test results.

Dietary and Lifestyle Modifications:

CALCIUM STONE PREVENTION

As a general rule, the following items are troublemakers for calcium-containing stone formers:

• Inadequate fluid intake: The most important way to prevent stones is to keep the water flowing. Daily urine output should be at least 2 quarts daily. The amount of water required to achieve this goal varies from one individual to another. If you are sedentary, it may simply require drinking eight 8 OZ. glasses of water daily. However, excessive sweating, constant exposure to dry air (a humidity of 40-45% minimizes fluid loss), and excess intestinal fluid loss increase the amount of fluid you need to drink to maintain 2 quarts of urine output daily.
  • Tips: Every time you pass a water fountain, take a drink. Drink a glass of water when you brush your teeth, one to two glasses with each meal, one or more glasses between meals, and before bedtime. At least half of the fluid should be water. Avoid tea, colas, excessive milk consumption, and drinks that are loaded with sugar (usually in the form of high fructose corn syrup). If you work in a job that makes it difficult to drink adequate fluid during work hours, drink extra water before and after work.
  • Weekend warriors also require additional fluid intake to match their activity. Vacations require special attention as well. Avoid excessive sun exposure, binge eating, and excess alcohol consumption (yes, you can still have fun _).
• Excessive Oxalate: Oxalate is a waste product of metabolism. Stomach acid frees oxalate from food. Calcium binds oxalate in the upper intestine. Unbound oxalate is absorbed in the large intestine and excreted by the kidneys. Elevated urinary oxalate forms stones 15 times more readily than calcium alone! Sources that increase urinary oxalate excretion include each of the following:

  1. Diet is the chief source of oxalate. Therefore, people with oxalate containing stones should avoid consuming excess amounts of the following oxalate-containing foods: Cranberry, spinach, rhubarb, raspberries, tea, colas, cocoa, chocolate, wheat bran, peanuts. Canned foods can be a hidden source of excess oxalate: tomato sauce contains oxalate equivalent to 10 tomatoes! Click here for a list of foods that contain high, moderate, low, and nil amounts of oxalate.

  2. Excess vitamin C (above 1 gram daily).

  3. Excess dietary protein (see list below).

  4. Bowel disease. Problems also occur when insufficient calcium is available to bind oxalate in the small intestine. For instance certain types of bowel disease (e.g., gastric bypass, rapid intestinal transit, or problems with insufficient bile and/or pancreatic secretions that help digest fat) cause fat malabsorption. Fat gobbles up calcium and creates a “soap” similar to the soapy film that occurs when you wash your hands in hard water. Consequently, calcium is unavailable to bind oxalate. Therefore, excess oxalate is absorbed (because it’s unbound) in the large intestine and excreted in the urine. This scenario often leads to calcium oxalate stone formation.

  5. Severe calcium restriction (400mg or less daily) can have a similar effect because insufficient calcium is available to bind oxalate. With rare exception (e.g., people who test results show excess intestinal absorption of calcium), a daily consumption of 800 mg of calcium-containing foods is safe.

• Excessive Calcium: Although much maligned, as stated above, moderate calcium consumption (800 mg or less daily) isn’t harmful in most cases. Scientific studies have also shown that calcium stone formers with an increased risk for developing osteoporosis can safely take 1000mg of calcium with food.
• Excessive Salt: Dietary salt is mainly excreted in the urine. Salt induces excess calcium excretion in stone formers. Excess salt also interferes with thiazide medication (water pills) used to treat certain types of calcium stone disease.
  • Tips: Remove the saltshaker from the table; don’t add salt to cooking– use spices instead for flavoring; say no to junk and processed food –read labels for sodium content; drain canned vegetables and rinse with water. Commercially softened water is also high in sodium (salt).
• Supplements: Vitamin D increases calcium absorption and vitamin C above 1 gram daily may increase oxalate. Furthermore, health foods may contain excess oxalate – read labels.
• Excessive protein: Excessive protein intake can increase calcium stone formation because it:

  1. Makes the urine more acidic. Acidic urine decreases the excretion of citrate - a natural stone-inhibiting substance made by the kidney and excreted in the urine. Citrate retards calcium, oxalate, and phosphate crystal formation.

  2. Increases oxalate formation and urinary calcium excretion. Two breakdown products of protein metabolism increase the risk of calcium stone formation: glycine is metabolized to oxalate, and methionine drives more calcium into the urine.

  3. Increases the risk of uric acid stones (see below). Uric acid stones can attract calcium crystals to form uric acid-calcium oxalate or urate-calcium oxalate stones.

Therefore, stone formers should limit their protein intake. The following is a general guideline of daily protein requirements for stone formers:

• 95-114 pounds – 35–42 grams
• 115-134 pounds – 42-49 grams
• 135-154 pounds – 49-56 grams
• 155-174 pounds – 56-63 grams
• 175-194 pounds - 63-70 grams
• 195-214 pounds - 70-77 grams
• 215-234 pounds – 77-84 grams
• 235-255 pounds – 84-91 grams

• Restrict meat protein by making your portions no bigger than a deck of playing cards. If you can’t resist, and end up eating excess protein; drink an extra glass of water or two to compensate. Also avoid eating a high protein meal late at night. Urinary output at night is much less than during the daytime, so nighttime urine is more concentrated and acidic. A burst of excess protein late in the evening compounds the problem and increases the risk of stone formation.

• Excessive calories: Calorie rich food increases the burden on the kidneys and produces acidic urine.
• Fad diets: In addition to being high in protein, many fad diets cause a rapid breakdown of muscle and fat. One of the waste products generated by rapid weight loss is an organic acid called ketone. Excessive ketone formation lowers blood pH. The kidneys compensate by excreting excess acid, thereby creating acidic urine. The end result is higher oxalate and lower citrate excretion.
• Insufficient fiber: Fiber binds oxalate; therefore insufficient fiber intake increases the risk of calcium oxalate stones. Eat 25-30 grams daily (read labels).
• Excessive sugar: Excessive refined sugar consumption increases calcium loss from bone. The excess calcium ends up in the urine and increases the risk of stone disease.
• Excessive alcohol: Alcohol is a diuretic –it increases urine output. Therefore, unless water intake matches fluid loss, alcohol consumption causes dehydration. Alcohol also prevents the kidneys from effectively excreting uric acid.

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How can I prevent Uric Acid Stones?

As a general rule, the following items are troublemakers for uric acid stone formers:

• Low urine pH: Urine pH ranges from 5 to 8. A pH of 7 is neutral. Acidic urine ranges between 5 to 7 - lower numbers are more acidic. Alkaline urine ranges from 7 to 8 – higher numbers are more alkaline. At a pH of 5.75, half of the breakdown products of purine metabolism are soluble (dissolvable) in the urine as a urate salt, and half are insoluble as uric acid.

As the pH drops, the concentration of uric acid increases (and so does the risk of uric acid stones). On the other hand, the solubility of uric acid increases 11 fold as the urinary pH increases from 5 to 7. In other words, with less acidity more uric acid is converted to the soluble urate form. However, if the pH increases too much, it can cause another problem. High urate concentrations act like a magnet for calcium oxalate crystals, which can lead to calcium oxalateurate stone formation.

Normally after eating a meal, the urine becomes temporarily alkaline. In uric acid stone formers, though, this “alkaline rebound” doesn’t occur. Therefore, the urine remains acidic. In order to compensate, uric acid stone formers can raise their urine pH by:

• Increasing fluid intake.
• Dietary changes (see discussion above and below
• Medications such as urocit K and polycitra K

• Excess purine and protein intake: Foods that are high in purine increase uric acid production. Foods that are high in purine include each of the following:

1. Organ meets (beef, turkey, poultry, veal, pork)
2. Sea food (anchovies, salmon, herring, smelt, trout, shellfish)
3. Legumes (peas, beans)
4. Mushrooms.

Excessive protein intake also increases urine acidity. Follow the suggestions for limiting protein consumption listed above.

• Low urine volume: Concentrated urine is acidic. Follow the suggestions listed above for increasing fluid intake.
  
  
• Gout: Elevated blood levels of uric acid can precipitate gout. However, only 25% of gout sufferers form uric acid stones, and vice versa. Uric acid stone formers with elevated blood levels of uric acid are often treated with allopurinol (11-300mg daily), which blocks an enzyme that blocks uric acid formation.
  
  
• Special considerations: Laxative abuse induces loss of bicarbonate and potassium in the stool, which creates an acidic urine (and the formation of a special type of stone called ammonium urate stone).

Excessive intestinal fluid and bicarbonate (an alkaline solution) loss causes dehydration and metabolic acidosis. The end result is concentrated acidic urine. This includes people with intestinal diseases such as Chron’s disease, fast bowel transit disease, bowel resection, and ileostomies. In this situation, drinking sufficient fluid – enough to make at least 2 quarts of urine daily – and taking medications that alkalinize the urine (e.g. urocit-K®) reduces the risk of uric acid stone formation.

• Medications: Thiazide diuretics are often used to prevent calcium stone. A side effect of these medications is increased uric acid production. Medication that alkalinize the urine (urocit K®) can prevent this problem. Chronic ingestion of salicylates (aspirin-containing medications) also increases urinary uric acid excretion.

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