Prevention

Introduction

Most people who have formed even a single kidney stone probably have a genetic predisposition to making stones. Although the concept of prevention is proven and worthwhile, it s important to understand that certain people will always be more likely to make stones in the future, even if they follow all the correct advice strictly.

There is a lot of misinformation with regards to prevention of stone disease (also called stone prophylaxis). Many people waste a lot of time and money on unproven remedies and it is therefore appropriate to first list what has NOT been proven to prevent renal stone formation.

Remedies with NO Benefit

Many people are attracted to the idea of “natural remedies” as they sound safe and are promoted as healthy and side effect free. In fact, many of these substances do have side effects, can be costly and are of no clinical benefit. Just because a particular substance is promoted on a website does not mean it works.

There is no evidence that the following reduce kidney stone formation:

  • Vitamins.
  • Herbal remedies.
  • Naturopathic substances.
  • Exercise.

Medical Practitioners are always keen to recommend substances which are tested, proven and have a well-documented side effect profile.

Proven Strategies

The following strategies have been proven to reduce the likelihood of kidney stone formation:

  • Increasing oral fluid intake.
  • Dietary Modification.
  • Medical prophylaxis – long term medicines.

Of these three proven strategies, fluid intake is the most important.

Fluid Intake

There is good evidence that increasing urine output by drinking more fluid reduces the risk of forming kidney stones. Increasing urine output results in urine which is more dilute. In other words, there is a lower concentration of chemicals which can form stones in the urine.

It has been shown that people who maintain excellent hydration long-term can reduce the likelihood of stones forming by about 50%.

Type of fluid

It was previously thought that drinking water was best. However, more recent studies suggest that the type of fluid consumed does not matter as all fluids contain water and all fluids will increase urine output and reduce the concentration of chemicals which form stones in the urine.

There is evidence that alcohol (including beer), tea, coffee, juice and mild are all as effective as water. Patients were previously advised to avoid tea as it contains oxalate which is a common component of kidney stones, but despite this, tea seems to be very good at reducing kidney stone formation.

There was some evidence that sweet carbonated soft drinks may increase the risk of stone formation, but more recent evidence suggests this is not the case.

How much fluid should be drunk?

People who have formed a kidney stone in the past should consume enough fluids to ensure they produce at least 2500ml in a 24-hour period.

A specific volume to drink is not specified as many foods such as fruits and vegetables are full of fluids. Different individuals will also loose variable amounts of fluid in the sweat.

It is very difficult to estimate a urine output – hence it is recommended that patients measure their total urine output over a 24-hour period.

As a rough guide, the colour of the urine can also indicate if an individual in adequately hydrated. Stone prevention requires the urine to appear very dilute, in other words, the urine should be as clear as water or only slightly yellow.

The main disadvantage of increasing urine output is that people will have to visit the toilet more frequently. In order to minimize passing urine over night, the majority of the fluid intake should be consumed before 8 pm.

It is also worth noting that this advice to drink more fluids only applies to patients which have previously formed kidney stones. The vast majority of the population are not prone to stone disease and will not form calculi even if they are very dehydrated.

There is no evidence that drinking plenty of fluids has any general health benefits. Most people should simply drink when they are thirsty is the same way as humans have done for thousands of years and in the same way all other animals drink. It is an old wives’ tale that drinking more fluids is good for you.

Timing of drinking

Stone formers should drink plenty of fluids throughout the day. Fluids should not be consumed in the last couple of hours prior to bedtime or overnight to avoid having to void at night.

Dietary Modification

Changing the type of food intake may reduce the likelihood of stone formation but this seems less important than fluid intake. There is relatively little evidence that dietary modification works well, but some changes are worth making. People will not persist with dietary modification if they find this too difficult or restrictive. It is therefore advised to aim for a well balanced healthy diet without become too extreme about restrictions.

Increasing Calcium Intake

Even though the majority of kidney stones are composed of Calcium, there is good evidence that a diet rich in calcium is associated with a lower chance of making stones in the future. Interestingly, calcium supplements (as opposed to dietary calcium) may slightly increase the risk od renal stone formation. If calcium supplements are necessary, they should be taken with a meal as this may reduce the likelihood of stone formation

Dietary Calcium is found in:

  • Milk and milk products – milk, yoghurt, cheese and buttermilk.
  • Leafy green vegetables – broccoli, collards (cabbage family), bok choy, Chinese cabbage and spinach.
  • Soy and tofu – tofu (depending on type) or tempeh and calcium fortified soy drinks.

Reducing salt intake

A high salt diet is associated with an increased risk of stone formation. It is important to note that salt is present as an additive in many processed foods.
High salt intake causes increased concentration of Calcium in the urine which may cause stone formation.

Low Protein Diet

A reduction in animal protein (meat, fish, chicken and eggs) may be beneficial especially in those who produce Uric Acid or Calcium stones.

Low Oxalate Diet

This is controversial and the author would not recommend this. Many stones are composed of Calcium Oxalate. Oxalates are present in many types of healthy food groups and avoiding oxalate can have negative consequences. There is some evidence that reducing dietary oxalate can reduce the concentration of oxalate in urine. However, there is no conclusive evidence that this results in less stone formation.

The following foods contain oxalate:

  • Tea.
  • Chocolate.
  • Nuts.
  • Cocoa.
  • Strawberries.
  • Rhubarb.
  • Celery, Spinach and Beetroot.
  • Parsley.

High Fruit and Vegetable Diet

Apart from the general health benefits of fruits and vegetables, there is evidence that this increases the concentration of Citrate in urine and this helps to prevent the formation of renal calculi.

Medical Stone Prophylaxis

Medical Stone Prophylaxis is also known as Medical Stone Prevention. It is possible to reduce the likelihood of kidney stone formation with the use of medicines. Only medicines can actually change the chemical composition of urine significantly. Although drinking plenty of fluids and modifying dietary intake are both effective, for some patients this is insufficient and consideration is given to taking medicines.

Medical therapy for stone prophylaxis (prevention) is not used for the majority of patients as many people will only make a single stone or a few stones in their entire life and taking medicines is simply not worth it for such individuals. Medical stone prevention is suitable for:

  • Recurrent stone formers.
  • Patients who present with numerous stones.
  • Patients who continue to make stones despite fluid / dietary modification.
  • Patients who have required a few surgical interventions.
  • Patients who cannot tolerate recurrent stone.
    • Frequent travellers.
    • People living in remote areas.
    • Pilots.
    • Patients who tolerate anaesthetics poorly.

Not all patients are willing to have medical therapy to avoid future stones. This therapy requires a long-term commitment, as medications need to be taken indefinitely. There is little use staying on these medications for only a few months, as they are only effective when they are taken for years. Many individuals cannot be bothered and do not wish to take tablets for ever, which is perfectly understandable.

Medical stone prophylaxis requires a careful Extensive Metabolic Evaluation which includes at least two 24-hour urine collections, blood tests, stone analysis and imaging of the kidneys. Following these detailed investigations, patients are commenced on medications. The type of medication patients are given depends on the biochemical abnormalities detected in the urine and the composition of the kidney stones. The 24-hour urine tests then need to be repeated to make sure the medicines are doing their job properly by changing the chemical composition of the urine. This is all a big commitment and a nuisance for all but a small proportion of recurrent stone formers.

Choice of Medication

The exact medication used to prevent stone formation depends on a person’s urinary chemistry and the results of chemical analysis of the stone. This is a list of some of the medications used and the type of abnormalities they are designed to correct.

  • Thiazide Diuretics e.g. hydrochlorothiazide.
    This medication is used for patients who have an abnormally high level of urinary calcium (hypercalciuria) and evidence of calcium stone formation. It has been proven to effective in many clinical trials. Side effects are uncommon but can include fatigue and biochemical abnormalities. Patients taking this medication require blood tests a couple of times a year to make sure their potassium levels are not too high.
  • Potassium Citrate e.g. Urocit-K.
    This medication is used in patients who have been found to have a low urinary citrate level. Citrate is an inhibitor of stone formation and low levels of citrate have been shown to increase stone recurrence. This is largely used for patients who form calcium stones but is also proven in patients who make Uric Acid stones associated with an acidic urine. This medication is very good at making urine more alkaline (less acidic) which is useful for most Uric Acid and Cystine stones. Interestingly, Potassium Citrate has also been shown to be effective in patients where no specific biochemical abnormality has been detected on urinary testing. Side effects are uncommon and include nausea, vomiting and diarrhoea.
  • Allopurinol e.g. Zylopim.
    Allopurinol reduces blood and urinary levels of Uric Acid. Interestingly, most patients with Uric Acid stones do not have high urinary levels of Uric Acid and do not require Allopurinol. This medication should be used in patients who have either calcium or Uric Acid stones where there is proven hyperuricosuria (high levels of Uric Acid in the urine). Side effects are uncommon but some patients may be allergic to Allopurinol.
  • Thiol medications e.g. Tiopronin.
    This drug binds to Cystine in the urine and may be used in patients who form Cystine stones. These stones are very uncommon. Thiols are usually used in combination with Potassium Citrate which is the first line treatment for such calculi.
  • Acetohydroxamic Acid (AHA).
    This rarely used medication is used in patients with severe recurrent infection related kidney stones. Ideally these stones need to be completely removed surgically, but if this is not possible, the above medication may be used to slow down further infection stone recurrence.