Urinary Stones

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DIETARY ADVICE FOR PREVENTING CALCIUM KIDNEY STONES

DIETARY ADVICE FOR PREVENTING URIC ACID KIDNEY STONES

DIAGNOSIS AND MANAGEMENT OF KIDNEY STONES (AUA)

 

Background

 

Kidney stones are very common, occurring in up to 10% of the male population and 5% of females. Recurrences are common. While stones do not usually cause long term problems when treated appropriately, they can result in significant pain, inconvenience and time away from work. The management of stones is individualized and takes into account:

  1. LOCATION of stone
  2. SIZE of stone
  3. COMPOSITION of stone
  4. SYMPTOMS: pain, nausea, vomiting, fever, etc.
  5. OTHER: complicating factors (e.g. infection), occupation, etc.

 

Causes

 

There are many reasons why kidney stones form. Fundamentally, stones form when the concentrations of solutes in the urine exceeds the ability of the solutes to remain dissoved. Crystallization occurs and the crystals grow larger with time into stones. Specific stone types have different causes.

 

Diagnosis & Evaluation of Urinary Stones

 

Most stones will present with symptoms of 'renal colic' - a constellation of flank pain (the area to the side of the back bone between the ribs and pelvic bone), nausea, vomiting and blood in the urine. Sometimes, the blood in the urine may not be visible. The pain is due to obstructed drainage of the kidney and the resulting back pressure. The pain may be severe and incapacitating - most women who have children describe the pain as worse than childbirth. In some cases, however, the symptoms may be less obvious. Urinary frequency and urgency with small volumes of urine may occur. In some patients, stones may not produce any symptoms at all, especially if the drainage of the kidney is not obstructed.

 

If blood and urine testing is done, there may be blood in the urine (hematuria) and kidney function may be impaired. Imaging (radiology) tests are almost always required to confirm the diagnosis. The imaging test of choice in most patients is a CT KUB (Computerized Tomography Kidney Ureter Bladder) which images the entire urinary system. There is no intravenous contrast/dye required so there is no risk to kidney function. The amount of radiation from the scan is minimal and similar to a plain X-ray of the abdomen. The actual scan itself takes less than 60 seconds on our 64 and 128 slice CT scanners. In some cases, ultrasound, plain X-ray films or a combination are used.

 

There are a few important things to note about imaging for stones.

  1. CT KUB: this is the gold standard and virtually every type of stone will be detectable. It is very accurate with respect to size and location. There is, however, a low dose of radiation. More information on radiation safety can be found here. A CT KUB has about 3 mSv radiation exposure. This handout provides a good summary of risk.
  2. Ultrasound: there is no radiation, so it is very safe - even in pregnant women. However, ultrasound has several disadvantages: it tends to overestimate the size of stones, may miss small stones, may mistake normal structures for stones, is not good at locating stones in the distal ureter. Often the presenence of a stone is inferred by the findings on ultrasound rather than direct visualization of the stone itself.
  3. X-ray (KUB - Kidney Ureter Bladder): this can only detect stones which are large enough and block X-rays (are 'radiopaque'). It cannot visualize very small stones or those with little or no calcium (e.g. uric acid). It is, however, helpful in determining if a stone can easily be treated with ESWL since fluoroscopy (a special type of 'movie' X-ray) is used to direct sound waves to the stone during this type of procedure. It is very easy and quick to perform - an appointment is usually not necessary.

 

Types of Kidney Stones

 

There are multiple types of kidney stones. While the vast majority of stones are contain calcium, there are other compositions. It can be helpful to know what the composition of the stone is since specific treatments can be targeted at the different stone types. The most common types of stone are:

 

  1. Calcium oxalate (the monohydrate form is harder than the dihydrate form): this is by far the most common type of kidney stone
  2. Calcium phosphate
  3. Uric Acid
  4. Struvite - also known as 'Triple Phosphate' or Magnesium Ammonium Phosphate
  5. Cysteine (rare)

 

Treatment

 

Our group of Urologists has extensive experience in managing the full spectrum of stone disease ranging from prevention to surgery. Our group performs over 550 stone cases per year including shock wave lithotripsy (ESWL), nephroscopy, ureteroscopy, laser stone fragmentation and removal of bladder stones. We have the most advanced endoscopic equipment available including a full-time dedicated fluoroscopic urology table to allow coordination of real time X-ray imaging and surgery of the urinary tract. We have flexible scopes to access the kidney through the body's natural conduits and lasers to fragment stones. We work closely with the Stone Centre at Vancouver Hospital to provide comprehensive care of patients with urinary stones.

 

At Richmond Hospital, we are able to manage stones on an expedited basis. Patients who have acute pain related to stones can often have their surgery within 24 hours, sooner if the clinical situation demands.

 

The approach to managing stones is 2-pronged

 

  1. Manage any stones which are present (management will depend on if the stone is producing symptoms or not) - this may involve medications, surgery or a combination.
  2. Prevent stone growth and recurrence by identifying pre-disposing factors. General preventative measures are always useful. Sometimes medications will be used to prevent specific stone types in select circumstances.

 

When should you NOT wait to have an obstructing ureteral stone treated:

  1. Obstructing stone with any suspicion of infection. The combination of a stone obstructing the urinary system (usually one of the ureters) in the setting of infection can be lethal. This is a urologic emergency because it can kill. The reason is that the bacteria in the infected urine are under high pressure in the upper tracts and can directly enter the blood stream causing 'septic shock'. Septic shock from the urinary system (urosepsis) can cause blood pressure to fall, multiorgan failure and ultimately death. Never, ever wait to seek medical attention if you have a high fever and flank pain.
  2. Obstructing stone with renal failure. Most people with obstruction of one of the kidneys have nothing to worry about - unless it is left untreated for several weeks in which case permanent damage to the kidney can occur. There are instances where renal failure can results from obstructing stones. These include bilateral obstruction (both sides blocked) or pre-existing problems with kidney function such that obstruction of one side causes serious problems with global renal function because it was already compromised.
  3. Obstructing stone with little chance of passage. The larger and higher a stone is in the ureter, the less chance it has to pass. While it is completely reasonable to consider observing a small stone (few millimeters or so) for days to a few weeks because it may pass, watching a stone with virtually no chance of passage on its own (e.g. a 1 cm ureteral stone) is almost alwasy postponing the inevitable. Some people are capable of passing large stones of a cm or more, but over 95% of people would not. Ultimately, it's up to the patient but if that 1 cm stone hasn't passed in a few weeks it wouldn't be rational to risk irreversible kidney injury by waiting longer.

 

 

Prevention of Urinary Stones

 

Stones frequently reoccur. Up to 50% of patients experiencing a stone will have a recurrence within the next 10 years. Whenever possible, prevention of stones is always a better alternative than treatment. Fortunately, there are some basic dietary changes which can significantly reduce the chances of stone recurrence. Note that the majority of stones cannot be 'dissolved' - a notable exception being smaller uric acid stones.

 

There are many different types of stones and therefore the dietary modifications we use to prevent stones is different. Some dietary changes are applicable to prevention of virtually all stone types.

  1. Aim for a urinary volume of 2 L/day - any fluid except sugar soda is good
  2. Limit animal protein to < 200 g/day
  3. Limit salt to < 6 g/day
  4. Increase your intake of citrate (esp. lemon and lime juices but orange and grapefruit are good also)
  5. Do NOT reduce your diary/calcium intake - aim for 1200 mg per day

 

PRINTABLE PATIENT INFORMATION

DIETARY ADVICE FOR PREVENTING CALCIUM KIDNEY STONES

DIETARY ADVICE FOR PREVENTING URIC ACID KIDNEY STONES

 

As long as you eat a healthy diet, we can work with this and decrease the chances of stone recurrence. Note that what is good for one type of stone may not be good for another type. Also, unless you has specific abnormalities on either your blood or 24-urine collection, dietary modification may not be necessary (note that increasing fluids and having a balanced, healthy diet will be helpful for everyone).

 

We are often asked detailed questions on dietary modification. Note that you do NOT need to eliminate any food completely. If the printable information does not answer your questions, read on!

 

 

Evaluation for Metabolic Abnormalities

 

In certain circumstances, testing of the urine and blood for predisposing causes will be undertaken. The urine is checked to see if there are factors which might be promoting stone formation - usually a 24 hour collection is necessary.

 

  1. 24 hour urine. A complete specimen spanning 24 hours is used. This checks for stone promoters (e.g. sodium, calcium, uric acid, oxalate, low urine output) and for stone inhibitors (e.g. citrate); cystine in children
  2. Blood tests. Best done FASTING (no food). We usually check for Creatinine, complete blood count, electrolytes (including sodium, potassium, bicarbonate, chloride, calcium, phosphorus), uric acid and parathyroid hormone
  3. Specialized blood testing for HYPERCALCEMIA or HYPERPARATHYROIDISM
    1. We often refer to an endocrinologist or head and neck surgeon
    2. SESTA MIBI Scan (to check if one of the four parathyroid glands are overactive)
    3. Blood tests: ionized calcium, 25 OH Vitamin D levels, albumin, PTH, phosphorus, creatinine
    4. 24 hour urine for calcium
    5. Bone Mineral Density scan to check for osteoporosis

 

Common Scenarios:

  1. Secondary hyperparathyroidism: serum calcium is normal but PTH is high. Vitamin D levels may be low. The underlying cause is usually low Vitamin D stores. Treatment:
    1. Vitamin D 3000 IU daily for 3-4 months
    2. Repeat Calcium, Creatinine and PTH levels. If normal, continue with Vitamin D 1000 IU indefinitely

 

Medications for High Urinary Calcium

 

 

Medical Treatment of Uric Acid Stones

These stones primarily result from low urine pH (acidic urine). When the urine pH (a measure of acidity) drops from 6.5 to 5.0, the uric acid becomes 10 times less soluble. Crystals can form rapidly in this environment, especially in circumstances where dehydration is present. When the urine pH becomes more alkaline (higher pH), uric acid crystals can dissolve - uric acid stones are one of the few that are actually soluble. However, high uric acid levels are still a problem because salt can crystalize with uric acid (forming monosodium urate) and predisopose to calcium stone formation. 

 

Because obese patients are far more likely to have acidic urine, uric acid stones are most common in these patients. Diabetes (more common in obese patients) also increases the acidity of urine - therefore obese diabetics are at markedly increased risk.

 

REDUCING URINE PH AND URINARY ACID LOAD IS THE MAINSTAY OF TREATMENT

 

 

Treatment of Cysteine stones

Cysteine stones are rare. They result from a congenital metabolic abnormality. Recurrences are frequent and the stones are very often difficult to treat. Prevention is important, primarily with medication. Diet modification is an adjunct.

  1. Thiola
  2. Alkanalizing agent (to a urine pH of about 7) K citrate 10-20 meq/day
  3. Captopril (up to 50 mg twice daily to bind cysteine starting from a low dose to start)
  4. Fluid output >2.5 L/day
  5. Low sodium (ideally less than 2 gram/day) - more important than in other patients.
  6. Limit protein in methonine-rich foods (very difficult to do since it is in virtually everything - animal protein, eggs, dairy which can compromise calcium intake)

Frequent imaging with ultrasound every months to pick up stones early is improtant.

 

Types of Stone Surgery Available Through the MVU Group

Extracorporeal Shock Wave Lithotripsy (ESWL)

Percutaneous Nephrolithotomy

Ureteroscopy and Nephroscopy/Renoscopy - Flexible and Semirigid

Laser Stone Fragmentation

 

On the Web

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UrologyHealth.org The patient information site of the American Urological Association.