CoeTie4There is no doubt about what I say to patients: ” Analyse every kidney stone. Bring in any stones you have tucked in a dresser drawer and get them analysed. Bring me all the analyses that have been performed on your kidney stones.”

But what do I say to me, and what do I do as time goes on and more stones form or are passed? Do I analyse every kidney stone?

Do you?

The problem of keeping track

Whenever I get a new patient, the stone analyses are at the top of my mind. How can I do anything rational about prevention if I don’t know what the stone crystals are? If there are no analyses at the first visit, like you I do everything I can to track them down; and, I usually succeed. But as time goes on with a patient, and more stones come along – many of them old ones, I hope – there is a tendency to let them go. After all, there were two calcium oxalate stones documented 2 years ago, I say to myself; do I really need to send more of them off in order to prove the obvious, or to meet some standard of perfection?

The problem is, at least in the patients I have studied, things change, and not always for the better.

Evidence for stone conversion

You probably already know that calcium phosphate stones, brushite especially, are much more trouble than routine calcium oxalate stones. What I suspected, and have had an occasion to document Nephrology Dialysis Transplantation Volume 24, Issue 1Pp. 130-136. is that conversion from calcium oxalate to calcium phosphate stone formation is not so rare among our patients with sequential stone analyses during treatment. Out of 4767 patients, we found 445 who had two or more stone analyses, lacked any systemic disease as a cause of stones, had well preserved kidney function, and formed calcium stones without any admixed uric acid, struvite, or cystine: were, in short, idiopathic calcium stone formers with at least two stone analyses.

I would have thought, incidentally, this being a stone research center, we would have had many more stone analyses for this most common kind of patient, but we did not. If it were not for our research, and if we were not maintaining such complete research records as we do, I would never have known we did not have more.

The details of what we found

Of the 445, 62 had a first stone >50% calcium oxalate by analysis and a last stone at least 20% higher in calcium phosphate content. These were the patients who converted from calcium oxalate to calcium phosphate stone formers. As controls we selected from the 445 181 patients who met rather stringent criteria: First stone >90% calcium oxalate and increase of stone calcium phosphate was <20%. In actual fact, the median stone calcium phosphate percentage of those who converted were 12% at the start and 75% at the end, whereas those who did not convert began with a median calcium phosphate percentage of 2% and ended up at about the same. Given only the most rigorously selected patients, 62/(62+181) or 25.5% converted.

In an altogether unrelated study of VA hospital stone analyses, Mandel et al found that successive recurrences of stone had increasing calcium phosphate percentages. They specifically echo our idea, actually antedate our presentation of that idea in print, that stone analyses should be continuous because conversion is not at all uncommon.

Why is increase of stone calcium phosphate important?

I have already pointed out that calcium phosphate stones are more serious a problem than calcium oxalate stones: they are larger on average, often more numerous, and involve the kidney epithelial cells. Brushite stones are very hard and do not fragment well with shock wave therapy. So conversion is not a good clinical outcome.

An altogether different problem is that treatment may not be the same for idiopathic calcium phosphate and calcium oxalate patients. We treat idiopathic calcium stone formers like you do: fluids, reduced diet oxalate, reduced diet sodium, thiazide diuretic agents to lower urine calcium when it is high, and potassium citrate, and use these modalities in various combinations depending on the situation. All of these treatments are reasonable, and the two drugs each have some RCT support.

But potassium citrate has never been tried in calcium phosphate stone formers per se. Some calcium phosphate stone formers no doubt have been in the three RCT for potassium citrate, but we do not know which ones they were, and whether perhaps they did poorly with the drug – had more stones, or perhaps stone growth.

There are reasons to believe calcium stone formation might increase or decrease. Potassium citrate can raise urine citrate and thereby reduce calcium phosphate formation. This is true because citrate binds calcium in a soluble complex leaving less to combine with phosphate, and also because citrate can inhibit the formation and growth of calcium phosphate crystals. But citrate is an alkali and can raise urine pH, and therefore raise urine calcium phosphate supersaturation. So we do not know if it is a good or bad treatment for patients producing calcium phosphate stones. Lacking a trial the matter is moot and wisdom dictates caution.

There are other kinds of stone conversion

It is not just increasing stone phosphate content that has taken me by surprise. Although I have not written a paper about them, I have patients who started as idiopathic calcium oxalate stone formers and began making mixed calcium oxalate – uric acid stones over time. They needed treatment to raise their urine pH. Some had become diabetic; some became obese; some just got old and lost some kidney function. But how many patients have done this I do not know. Occasionally struvite begins forming in calcium stone formers. Eventually the infection becomes obvious: stones become large and gnarled; the urine is obviously infected. But perhaps a more timely analysis would have hastened diagnosis.

What I have begun to do

My message to myself, which I am sharing with you, is that stone analyses are really important over time, and being not too expensive (I have no financial relationships with this vendor, it just so happened to offer me a convenient web site for a reference) is probably worthwhile for most stones that are removed from patients or passed.

I am changing my ways. I send every stone for analysis. I suppose some money will be wasted, but maybe in the long run a lot more will be saved. Even a single extra stone attack can be very expensive.

Should we do research about this topic?

At first thought research would seem practical, and likely to help me decide if my new way is right – or wrong. But the matter is both mundane and not so easily transformed into an experiment. To do what Mandel did, analyse successive stones and determine phosphate content is to do what has already been done. What we did has also been done except for the specific search for new uric acid or struvite appearing over time.

This leads me, at least, to say no. We have a decent clue as to what happens to patients, and the belaboring of the matter may not be worthwhile. Others may say I am wrong in this, and even wrong to do too many stone analyses.

Fred Coe MD

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  1. kp

    My son is 0 years old and last week his urine was cloudy dark. The urine test showed a lot of blood without any infection and ultrasound showed a kidney stone (4mm x 0-4 mm).
    He did not have any pain, He is healthy and active boy with a 3-year- medical treatment for several complicated surgeries on his intestine when he was under age 4 years old.
    we are waiting for hie doctor appointment for any necessary treatment. I gave him a lot of water and try to give him some herbal medicine and force him to do some jumping rope. I wish the stone can be broken and pass without any severe pain.

    • Fredric Coe, MD

      Hi KP, I presume his age is 10. Intestinal surgeries can lead to stones – super complex issue in children. He needs complex evaluation and thoughtful treatment. He is best off having at least some evaluation in a university based pediatric department with special skills in the GI and urological matters you have mentioned. Perhaps his personal physicians are themselves so specialized that they can do it all. That would be ideal. But to me evaluation and treatment would be very challenging. Urine oxalate may be high, urine pH too low, urine calcium too high – etc. And depending on the surgery there may be more to consider. Be sure the stone is analysed and keep copies of the report. I have not as yeet written about the bowel disease stone problem, so I cannot point to an article for you. Regards, Fred Coe

  2. Natalie

    I have been reading all this material, and am wondering what “lifestyle” actually means. I have been under extreme stress recently, and am wondering if this could have caused my stones. The last time I had a stone was 10 years ago, and I was taking care of my husband during his declining health, and going thru a very stressful time.

    • jharris

      Hi Natalie,

      I am sorry to hear about your stress levels and your husband’s health. Lifestyle does include eating well, exercise and how you manage your stress because we all have it. Many manage it by making unhealthy eating choices, not drinking, drinking too much alcohol, etc. So is your lifestyle a healthy one? In what ways do you cope with stress? Perhaps you were not taking care of yourself bc you were so busy taking care of him. You must take care of you so that these horrible stones don’t come back. Need me, write

  3. Natalie

    I have a stone – 5 mm and several smaller ones in my left kidney, and several small ones in my right kidney. What will they look like – what shall I look for as I strain my urine to catch when they pass? I have something that looks like fine salt – can feel them between my fingers.

  4. mandi

    I am 22 years old and currently 17 weeks pregnant. I just had my first stone removed via lithro. it was 9mm. The results of the send out were:
    1st Constituent 50% Calcium phosphate (brushite)
    2nd Constituent 40% Calcium oxalate dihydrate
    3rd Constituent 10% Calcium phosphate (apatite)

    I havent been able to really find any answers on prevention of future stones like these. Is there medications that can be prescribed to help prevent future stones like this?

  5. Sheila

    What does a “large & gnarled” kidney stone looks like?

    • Fredric Coe, MD

      Hi Sheila, I guess if I am to be graphic I had better be able to say it in words. This visual applies mostly to struvite stones and form in layers. I think of rugged, twisted; large means they fill up a large fraction of the renal pelvis even into the calyces to make a staghorn pattern. But gnarled is not just twisted it is like ginger. Does that help?? Regards, Fred

    • Fredric Coe, MD

      Dear Sheila, I think my original answer to your question was lost. It looks like ginger root. Large means it fills up much of the renal pelvis and even extends into the calyces to produce a staghorn appearance. Regards, Fred

  6. Christina Hansen

    I’m amazed and impressed by the amount of information here and your willingness to advise people. It’s wonderful to know that there are healers out there (not just physicians). Thank you, both for the info in these pages and for your dedication to helping people!

  7. Keckert

    Hi, I just passed my first kidney stone and have an appointment with a urologist in Scottsdale, AZ to analyze it. I have been told I have another one that is larger waiting to drop. I am a 56 year old woman and a raw foodist. I live on green juices, green smoothies and salads to control my RA. I eat bananas, strawberries, blueberries, spinach, walnuts, almonds, seeds and coconut water every single day. I eat other fruits and veggies but these are my main go to foods throughout the day. Green juice of celery, cucumber, spinach, kale, chard no fruit. Could this diet be the culprit to my kidney stones? Most of my foods are high oxalates and that concerns me until I get my stone analyzed. Thank you!


    I just wanted to say I used to have a stone about every two years and after I went on bp meds with a diuretic my stones went away. And came back when I lost weight and cut back on the bp meds. I don’t drink much of anything . Just a little water. Just never thirsty. Only with food. I’m going to try the diet and drink more water. MAYBE I should go back on the bp meds.

  9. Claire

    Hi, would you be interested if I sold you my kidney stone for research?

    • Fredric Coe, MD

      Hi Claire, I am afraid we do not need more stones! Also we would never purchase specific items for research. We do reimburse all research subjects in our NIH funded studies and offer a modest honorarium for their time and trouble, but moneys must never be enticement for scientific work. Thank you, anyway; Regards, Fred Coe

  10. Robin

    Hello. I’m 42yrs old (female) and passed a kidney stone for the first time 8 months ago. I passed another stone two weeks later, and then another 3 months later. A few weeks after the third one I had a bad reaction to valtrex (prescribed for cold sore) and it caused impaired kidney function for a few days. Imaging done at that time showed many small stones in both kidneys. I’m pretty sure I either passed another stone last night or its on its way. The only stone I was able to catch was that first one but no one wanted it. My primary care dr said to give it to the kidney specialist but I lost my medical insurance and wasn’t able to keep that appt. The stone has since been lost.
    I’m curious what may have changed to cause me to suddenly have kidney stones. Is this typical as we age?
    Thanks in advance.


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