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. Luke

    Dr Coe, first off thank you for this incredible source of information, of which I will be diving deep into over the next few weeks.

    Quick question if I may.

    I was just in ER for a kidney stone, and have passed and collected the stone at home. I do not have insurance, but would like to get the stone analyzed. From your article I am correct in understanding this is the lab I can send the stone to be analyzed?

    Frustratingly I’ve searched for hours on Google trying to figure out how I can send the stone somewhere to analyzed, and I have had ZERO luck figuring that out. The closest I’ve come is on Amazon…..not sure if that’s legit or not.

    Are there specific tests or procedures I need to recommend to the linked lab above to ensure I get the most accurate composition as I want to do EVERYTHING in my power to prevent further stones and understand accurate composition will assist in that.

    Thank you so much for putting all this information together, truly grateful to have found this resource.

  2. Robert Scheffler

    I passed 1 large stone and 3 smaller stones. The large stone seems to be one or more smaller black stones encased in an outer shell that is smooth and brownish yellow in color. The smaller stones are smooth and the brownish in color. I do not have insurance or a doctor, is there anyplace I can get these stones analyzed??? Thanks in advance.

    • Fredric L Coe, MD

      Hi Robert, You do need a physician, and the stones analyzed. First, save the stones for when you get some insurance – just put them in a clean envelope in a drawer. Most medical schools do some free or reduced cost care and I would much advise you look around. Too many stones to let them just form. Fred

  3. Jeff Zoukis

    Dear Dr. Coe, I found your piece very interesting. Over my lifetime I have passed kidney stones and have lithotripsy on one of the original dorenier lithtrypsy machines in CA. Since my episode over 30 years ago I have had one serious Gall stones episode which passed naturally while in an emergency bed with morphine for pain. I am still wondering if there is a similar chemistry in the formation of both in the body. But recently even as of today I passed small mostly soft particles in my urine I can’t really call them stones as they are not hard. I typically retrieve them from my urinal and I have analyzed them earlier on when they were harder and they were lab tested as calcium oxalate stones. However on a regular basis when my diet is more in grain and nuts and often proteins high rich I seem to produce them more often. When I place them between my thumb and fore finger and rub the material fragments and sometimes seems sandy in part. I definitely feel them passing through my penis but it is not painful just noted. Probably 2- 5mm at most. Because they are mostly soft lately I wondered if you might suspect they form lower in my bladder. I would be pleased to hear your thoughts on this. I am on synthroid for my thyroid and atorvastatin and also thought could play some part. I also take Ibuprophen for my back pain for moderate scoliosis and question how these drugs may contribute. I try to consume citrus regularly in oranges mainly and some lemons to try to keep my acidity level higher having read that alkalinity is likely culprit. This is a wonderful world we live in where we can share so much information over the Internet with people like you and hopefully learn from both sides. Sincerely, Jeff Z.

  4. David

    I recently passed a kidney stone. Where can I get it tested to determine what kind of stone it is? Thank you, David

  5. Diane

    I passed a small fragment of a stone. The analysis said they were unable to identify the stones constituents.
    Is this common? What does this indicate?

    • Fredric L Coe

      Hi Diane, It says that perhaps the fragment contained no crystals, or that the lab was not able to get a spectrum off of the sample. It is not common and not ideal as you do not know what you are trying to prevent. It indicates your approach to prevention is a little more open minded than would be ideal. Here is a good prevention article, see if it helps you. Regards, Fred Coe

  6. Joe

    In have about 6 kidney stones (largest ~5mm) in my right kidney, one in my left they are believed to be calcium oxalate based on analysis of previous stones . I have not passed a stone in about 8 -9 years since last laser litho, yet most of these have all formed since. One stone remained in my kidney after surgery. I have had two laser litho’s and one ECSWL since about 1991. I have changed urologists because my previous urologist , while bent on doing further surgery had done nothing to advise on prevention or get to the root cause. My previous urologist mentioned Randalls Plaques but promptly forgot he said that 6 months later, thus triggering my change of providers. My new urologist had me on a 24 HR urinalysis and right away found I had low urine volume at 1.7 liter and also found that I am supersaturated with Brushite.

    My questions:

    1) Am I likely to be forming calcium phosphate stones given this new discovery?

    2) The stones apparently are ‘fixed” and not moving. Should I take a wait and see approach given the risks of surgery (I am 65 and have complicated medical conditions, Hemochromatosis, Mitral valve calcification)

    3) Would robotic per-cutaneous surgery be a less risky option? Go in and get them all?

    4) Are there any nerves inside the kidney itself? I have intermittent RLQ pain and yet no stones are moving.

    5) I have a small stone in my prostate is that a problem?

    6) While I am working to improve my water consumption, I understand that nothing will dissolve the stones. Is this correct?

    • Fredric L Coe

      Hi Joe, stones that do not obstruct or cause pain or bleeding, or become infected can be left alone or removed as an elective choice. I cannot predict your stone type based on the 24 hour urine SS, but if brushite SS is high and CaOx is not, it is quite possible. PERC is a big procedure, and ureteroscopic removal greatly preferable if your surgeon considers it viable for your specific case. Prostate stones are trivial. More water is always a good idea but prevention always requires more. Here is a good starting place to read in. Regards, Fred Coe

  7. Brian

    I have had recurring stones for some years now. As long as I can remember they have always been in the left kidney.
    Would this steer your advice for prevention in a different direction than what you’d advise for patients who get them in both sides?
    Is that normal? Or do they normally occur in either and/or both sides for reoccurring patients?
    Thank you for your time,

    • Fredric Coe, MD

      Hi Brian, Years ago I actually looked into this question. I decided it was just chance plus how crystals work. If you start forming them, they template each other so the chance of more rises with more crystals. But the other kidney remains at risk, so prevention is for both. Regards, Fred Coe

      • Tony Brine

        Many thanks for your many years of work In this area. Also thanks for your down to earth approach to some of these highly scientific issues. I believe you would be making a significant contribution at all different levels. I have been suffering with Uric acid stones for five years now ( I am 68 years old) and they are always occurring in my left kidney. I live in Western Australia and my doctors and specialist are pushing me to use allopurinol for the rest of my life. This seems to be a standard medical protocol over here. I have checked the side affects of this drug and feel somewhat uncomfortable about using it. I am not and have never been on any medication over a long term and have avoided painkillers and whatever drugs over my whole life. From my limited research pH levels seem to be the critical component and I like the idea of potassium citrate 40 mEq and potassium bicarbonate 20 mEq per day, in two doses as you proposed in your earlier article. I did discuss this with my doctor and he admitted he had no idea. Do you think I have anything to lose by trying this and getting a blood test before and then maybe after a month to see the affect on the Uric acid levels? Kind regards Tony.


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