CoeTie4At the end of it all, the science, the medical visits, the surgeries, what we really want is to prevent new stones. That is the main goal. Modern surgery is a blessing for those with stones. But no surgery is far better than even the most skilled and effective surgery.

Prevention of stones is orderly and occurs only over time.

Here is how to do it.

This article is designed to go with my other one which tells how to organize your medical visits so as to achieve these steps. 

What is the Science of the Five Steps?

Stones are made of crystals.

Supersaturation drives crystal formation and growth – this is a physical law that must always apply.

Supersaturation measurements are widely available from commercial vendors.

Because people who are actively forming stones are forming crystals their supersaturations are too high – crystals are forming – with respect to those crystals.

Lower the relevant supersaturations and you must lower formation and growth of those crystals in their stones.

With respect to the most common stones, calcium oxalate and calcium phosphate, and uric acid, supersaturation in urine depends mainly on volume, calcium, oxalate, citrate, and pH. You can lower supersaturation by altering any or all of these in a given person and so far as crystals are concerned the effects are much the same. 

1. Know the Stone Crystals

Stones are made of crystals: No crystals no stones. Prevention is prevention of crystals.

Analyze Stones

The proper way to know the crystals is analysis of stones and their fragments. Stone analysis is not expensive. If imperfect, it is the best we have, so use the service liberally. Stone crystals can change, and therefore prevention can need to change direction. There is no reason to discard a stone without analysis just because we think we know the answer.

Uric acid stones are remarkably easy to treat by raising urine pH and require little more discussion.

Cystine stones arise from hereditary kidney transport disorders and require special management.

Struvite stones arise from infection and require special combined surgical medical management.

Drug stones, ammonium acid urate stones, and rare stones – eg. 2,8 dihydroxyadenine stones require special management.

The vast proportion of kidney stones are calcium oxalate and calcium phosphates and uric acid, and this article refers mainly to them.

Guess if You Have To

Red or orange stones probably contain uric acid. Likewise, stones that do not show up on simple abdominal flat plate x rays are probably uric acid. These are easy to prevent, and recurrences are unnecessary.

Allow me to elaborate on this. Pure uric acid stones are almost all due to an excessively acid urine pH, and will stop if you raise that pH. Potassium citrate tablets, 10 mEq size, 2 twice daily is almost always enough. Sometimes it takes 2 tabs 3 times a day. Crystal light lemonade has in one liter about the same amount of alkali as two of the tablets. I could say that there is little excuse for another uric acid stone.

If stones contain uric acid and other crystals, those other crystals need to be dealt with on their own. They may not respond to higher urine pH, and could be worsened.

Yellow stones are probably cystine, and due to cystinuria, a complex disease with its own special treatments. Because almost all kidney stone panels include a cystine screening test, cystinuria is almost never missed. A positive test, however, can reflect cystine trait and the stones can be something else. So it is the negative test that is fully informative.

Small black stones are probably calcium oxalate, and large very homogeneous hard stones are probably brushite. But one cannot be sure.

Big stones that fill up the interior of the kidney are usually cystinestruvite – from infection, or calcium phosphates from alkaline urine and hypercalciuria.

But guessing is not a good way to achieve prevention. Find out whenever possible what crystals you are trying to prevent. Any stone fragment can be analysed. Never pass up an chance to be sure.

2. Obtain Proper Blood and 24 Hour Urine Measurements

I prefer two 24 hour urine kidney stone risk panels as a minimum along with at least one set of fasting blood measurements.

Screen for Systemic Diseases

Here is a table of systemic causes any physician can follow using the blood and 24 hour urine testing. This is not something a patient can do anything about except see that it is accomplished.

Revised Table for Evaluation for Systemic Causes of Stones

The bowel diseases that cause enteric hyperoxaluria – small bowel resection, malabsorption, are usually obvious, as are ileostomy and bariatric surgery.

Medullary sponge kidney and nephrocalcinosis are complicating features physicians need to deal with. Medullary sponge kidneys actually form tiny micro crystals in their dilated ducts. Whether these grow to become clinically important is not clear.

Nephrocalcinosis simply means many crystals are present on x ray images. During ureteroscopy these crystal deposits can be sorted out into real stones and plugs within the terminal ducts of the kidneys. Pain without obstruction is widely described in both of these conditions which complicates management.

Measure Urine Supersaturations of the Stone Crystals

Standard 24 hour urine kidney stone risk panels give supersaturations along with the urine chemistries that control those supersaturations. These are the keys to prevention. Supersaturations control crystallization and can be measured reliably in people. If crystals are being formed the supersaturation is too high and we need to lower it.

Read Your 24 Hour Urine Reports

Your physician will take care of you but a prepared and educated patient can make that care vastly more effective and reliable.

You can understand your 24 hour urine tests and follow along with your physician during your visits and when treatment has been introduced and your urine chemistries change as a result. The details of interest are different for calcium stones and uric acid stones, so I have put them in two separate articles. Do not be put off by all the numbers. Follow the articles with your test panel in hand and you will find things are not so difficult.

Stone prevention is long term and involves changes in diet and behavior and, often, medication use. If you can read your own report you will have a first hand sense of why your treatments are good for prevention and whether your treatments have achieved what they were designed to achieve.

3. Lower By Half the Supersaturations for the Crystals in Stones

There is no one way to reduce supersaturations. Every patient will have a characteristic pattern of abnormalities and supersaturation can be lowered by changing any number of those abnormalities present. Below is my general strategy, but it may not apply to you. If your urine volume is already very high, for example, to raise it would be silly. So consider my ‘strategy’ a general set of rules, easily modified to fit the individual situation.

Raise Urine Volume as High as is Practical

Above 2.5 liters daily is ideal. The site is very rich in advice for fluid treatments. How to drink more. How to get variety. How to avoid low flow periods. Being without cost or risk, fluids are always my first choice.

Reverse Urine Abnormalities Raising Supersaturations for the Crystals in Stones

urine calcium oxalate volume and citrate vs risk of stones from Curhan plotted with identical risk axesIdentify the factors in the 24 hour urine beside volume that are raising supersaturations for the crystals in stones, and act so as to reverse them toward normal. Common ones are high urine calcium, high urine oxalate from diet, low urine citrate, and low urine pH – for uric acid stones. High pH is a risk factor for calcium phosphate stones but one cannot lower urine pH under most circumstances.

Bang For the Buck

A vulgar phrase, if you think about it. Here are the relative risks of becoming a stone former in the three cohorts of nurses (red) and physicians (males, blue) Dr. Gary Curhan followed. You might say relative to what. For each risk factor it is different: Calcium – less than 100 mg/day; Oxalate – less than 20 mg/day; Citrate – less than 300 mg/day; Volume, less than 1 liter.

The average relative risk is at the end of the crosshatched bars. The ends of the solid bars are the 95th percentiles. When the solid bars are above one risk is certainly present, so you can see the safe ranges for calcium, oxalate, citrate, and volume. Because the plots all have the same risk ranges you can compare these four risk factors. Calcium has the widest  effect range. Oxalate is next and increases risk at even 25 mg/day. Citrate causes risk only when below 400 mg/day, and volumes above 2 – 2.24 liters lower all three cohorts into a low risk range.

Although urine volume confers relative risk equivalent to high urine calcium and oxalate only when below 1.25 liters daily (see graph at left), one always wants to raise it as much as is possible because such treatment is without risk or cost. Above 2.25 liters daily is ideal. The site is very rich in advice for fluid treatments. How to drink more. How to get variety. How to avoid low flow periods.

Obtain New 24 Hour Urines to be Sure Supersaturations Have Fallen

There is no point to changing diets or medications without proper follow up to determine if what was done had the desired effects. Six weeks is a good time for the first follow up measurement. Continue measurements until the supersaturation goals have been achieved.

4. Obtain more 24 Hour Urines if New Stones Continue

Crystals follow physical laws and supersaturation is what drives them to form and grow. Continued stones with reduced supersaturations means either supersaturations need to be lower, the 24 hour samples are not being taken on representative days, or the days themselves have periods of low urine flow or other breaks in treatment.

Crystals do not sleep nor do they make mistakes. Any chances they get, they use.

Physicians are trained to ferret out the details of a patient’s history that matter here. It is my main clinical expertise. 

Patients are not trained but they are the ones sitting up close at the 50 yard line. So they know more than anyone else. They just may not know what is important for stone prevention.

5. Follow Up Every Year Thereafter Even If Free of New Stones

OH, you might say, those urine measurements cost money.

They do, hundreds of dollars for each one.

The merest surgery can cost near to or even above ten thousand dollars when you consider the total of medical, operating room, anesthesia, and pre and postoperative imaging costs, and the inevitable emergency room visits that provoke the surgery in the first place. This is not to mention lost time from work.

And, did I speak about pain, misery, infections?

It it time for blunt talk. Lab measurements are the compass and altimeter. Flying blind is silly.

A Good Way to Get All This Done

You cannot do the five steps alone, your physician is crucial. He or she cannot do them either; you are crucial. In case you missed it, here is my view on how a patient and physician can best partner for stone prevention

That’s It

This site is far from complete but it already has a lot of what one needs to carry out these five critical steps. Do them and new stones will cease altogether or at least greatly reduce in frequency. If it does not work, one or more of the steps need correcting. After nearly 45 years preventing stones, I have become bold enough to say this, and mean it.

Good Luck, Fred Coe


  1. Cindy Prince

    Hello, Dr. Poe, and thank you for your time.
    Is lithotripsy not reliable for Calcium Oxalate stones? I had an ER visit 5 years ago for a kidney stone; had ‘several stones’ in my left kidney. F/U with Urology for a 24 hr urine, nothing else. I have had ~ 2 episodes of pain/year since that time (always relieved with hydration) until 4 months ago, when I had 3 episodes in Oct, unrelieved with hydration, but 1 Vicodin relieved pain each time. Finally in Jan this year, I had another ED visit. 4 days later passed a 5mm black stone; F/U with Urology last week : he stated I had several stones in the Left, largest being 15 mm, and would need percutaneous nephrostolithotomy, Neph tube x1 week. Right kidney has multiple stones, largest being ~ 7mm. For that side he would do outpatient Ureteroscopy with stent x1 week. He gave me an oxalate food list, and did a 24 hour urine, which I do not have the results of at this time. He stated Lithotripsy doesn’t work well. ? I am a bit overwhelmed at the thought of TWO surgeries in the near future. Do the stones have to be removed? Only because of their large size? Any thoughts would be helpful. Thank you. I am 64 years old, semi-retired RN. No other health issues, except Glaucoma.

    • Fredric Coe, MD

      Hi Cindy, SWL works fine for such stones but has a special place – usually one stone and not too big. Ureteroscopy is replacing shock wave because it can assure a stone free kidney. If you have multiple stones your physician is doing the right thing. Prevention is crucial and the article you are commenting from is a good one. Try to follow it and see if it does not take you where you need to go. As for need for removal, it depends on size and other specific factors to the individual. Regards, Fred Coe

  2. Joe A

    Dr Coe, I have a 30 year history of stone formation. Presented at age 20, then not again until age 31 when Lithotripsy was performed and now in the past 2 years I’ve had surgery to remove 19 bilateral stones up to 4 mm……18 months later (today) I have 18 NEW stones bilaterally even with sodium restrictions of 1200 mg/day and 66-120 oz lemon water as day in that time frame.
    At this point I am looking for an expert level referal in the Phoenix AZ area (possibly Mayo AZ Kidney Center).

    Any Suggestions? Thank you, Joe.

    • Fredric Coe, MD

      Hi Joe, I do have suggestions. Anyone with 18 new stones is in trouble and things are confused. Sort things out and prevention is practical – especially with lots of stones. The article has five steps, you do not mention the kinds of stones, or your 24 hour urine results. Somehow stones are being promoted and you need to know what they are and what is in the urine. This is always productive of prevention. Always. Regards, Fred Coe

  3. Rachel

    I am a 33 yr old female. I had an ultrasound after suffering chronic UTIs and it revealed I have kidney stones. CT scan confirmed I have 3 stones in one kidney and one in the other kidney, all measuring approx 3 mm. 24-hr urine testing revealed the following abnormalities: very high urine oxalate-114, citrate -491, pH 6.9, uric acid 1.07. The rest was in normal range: SS CaOx 5.5, calcium 85, SS CaP 0.61, SS uric acid .12. My blood work came back normal. My urologist explained the kidney stones are occurring due to my history of Crohns disease. It is strange to me since I have never had any GI surgeries, my Crohns is in remission, and the CT scan showed no current inflammation in the intestines. The only medications I am taking are 400 mg+ Calcium Magnesium Citrate and probiotics daily. He advised I consider undergoing shockwave lithotripsy and add B vitamins and potassium citrate and avoid high oxalate foods. He wanted me to also start allopurinol which I have not yet started. My blood uric acid levels are normal. What do you suggest in this case? I am in no discomfort from the kidney stones at this time and would prefer to pass them naturally. Is that advisable? Also, is high dose K citrate advisable given my situation? How about the allopurinol? Is it possible for me to lower my oxalate level to normal range with diet changes alone? My primary concern with all this is the potential for kidney damage.

    • Fredric Coe, MD

      Hi Rachel, given the extreme high level of urine oxalate, I am sure your physicians are concerned about primary hyperoxaluria. I would remove all sources of high urine oxalate and raise diet calcium intake to about 1000 mg from foods or if needed supplements taken with main meals and measure again. If this high level persists, you will benefit from evaluation at a major kidney stone diagnostic center. If the level falls, you will have an approach to treatment. Usually high urine oxalate from Crohns is after bowel resection as you correctly have surmised. I do notice the very high urine uric acid suggesting a very high intake of animal or plant DNA/RNA – protein sources have lots of cell nuclei – and that also can raise urine oxalate but not usually to these levels. The correct answer here is very important. Regards, Fred Coe

      • Rachel

        Thank you Dr Coe for your response and for your wonderful website. I feel like my urologist is either not aware or just not concerned about the potential concerns of my high urine oxalate and uric acid levels. He has not even mentioned primary/secondary hyperoxaluria. I am seriously concerned and I have radically changed my diet in response. I would very much like to get to the bottom of WHY my levels are so out of the normal range but I don’t know where to go. Would you advise I seek out a different urologist? Or is this something that I need to go to a pathologist? Geneticist? Nephrologist? And lastly, would you advise I take potassium citrate given my numbers?

        • Fredric Coe, MD

          Hi Rachel, The high urine oxalate needs to be understood and your own physician is the natural first source. If he/she cannot figure it out, perhaps a referral to a convenient nephrologist would help. More cumbersome but likelier to resolve matters, is there a university medical school nearby? Usually they have people who can deal with this level of complexity. Obviously high calcium and low oxalate diet with retesting is workable, and perhaps the urine oxalate will fall. But I am far away and high urine oxalate levels are worrisome so someone there needs to take care of this. Regards, Fred Coe

  4. Bromley

    Oxalate reducing enzyme website:


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