CoeTie4Hard unwanted objects made in the kidneys, stones can cause pain, bleeding, and urinary tract obstruction. Because stone surgery often infects the urinary system, and bacteria easily infect stones retained in the kidneys, infection follow stones like a shadow.

Stones surprise patients by their smallness, for all the trouble they cause, or by their largeness to think they passed through the urinary tract.

But small or large, many or few, stones provoke little love. Most who form them desire no more. Yet, left to themselves, stones recur. Over half of first time stone formers form another stone within 5 – 10 years. Once recurrent, stones form – on average – every 2 – 4  years.

So stone patients must pursue prevention and not imagine their disease will stop of itself.

Prevention consists in the search for causes and the administration of treatment. This site exists to guide both.

Crystals Make Stones Hard

Urine proteins molecules stick to tiny crystals and to each other as if designed to dispose of unwanted things. One can see in many morning urines tiny harmless crystal aggregates passed unknowingly and without harm.

In those predisposed, such protein crystal composites grow so large and numerous they can produce brief attacks of pain and bleeding but, being still too small to see on radiographs, escape detection. Such ‘crystal attacks’ are common in children with genetic hypercalciuria. Uric acid crystals can make a visible orange sludge or gravel.

When protein crystal composites grow grow big enough to obstruct the urinary tract and cause pain and we call them stones.

Very rarely urine organic molecules themselves make ‘soft’ stones that cause mild pain on passing.

Perhaps the true cause of stones hides in the chemistry of urine organic molecules, but for the moment these molecules are irrelevant to patients and their physicians. We do not know which ones most matter and about what is wrong with them that they permit stones we know essentially nothing.

So to prevent stones we work to prevent crystals. We search for causes of crystal formation, and act against them.

Stones are Crystal Artefacts

In human urine, calcium frequently crystallizes with oxalate and phosphate to produce the common calcium oxalate or calcium phosphate stones.

Other less common crystals form their own stones: Uric acid, a byproduct of nucleic acid metabolism; cystine, an amino acid that the genetic kidney tubule disease called cystinuria may liberate into urine in great excess; struvite, a crystal created by bacteria breakdown of urea, a normal urine constituent. Many drugs form crystals.

Because crystals can form independent of one another, many stones contain mixtures of them.

Like volcanic lava, an insect caught in amber, or the vague fossil tracings of some long lost species traced out in an otherwise indifferent rock, the crystals of a stone tell about a particular person with shocking precision and undeniable truth.

To find calcium oxalate crystals means such crystals were indeed once formed by that patient, and the same for all other crystals. Each crystal is a proof of past formation.

But unlike artefacts of a vanished age the proof in stones matters immediately, for in the person who made the stone those very same causes that once made its crystals may well yet operate and pose risk for more.

You might think such artefacts would attract the most intense interest and study. But no; stones are often discarded.

Stones Inform and Guide Prevention

Being as they are the artifacts and physical proof of past crystal formation, the crystals in stones guide all treatment. We can prevent stones only by preventing crystals. In any one patients the stones tell us what crystals we need to prevent. Otherwise than attend to the evidence written in stones we act in ignorance.

Stones are analysed by special laboratories

Specialized laboratories analyse stones at a moderate price.

One company has posted its prices. If you send the stone and pre-pay it is $40.00 with 2 photographs of the stone. Your doctor can get it for $35.00. This is only one of many companies that sell the service.

The report from any stone analysis laboratory is usually a single page that lists each type of crystal found in the stone and a rough approximation of the percentage of the stone each crystal accounts for.

The stones are powdered for the analysis. So a batch of stones will be cheap per stone but powdering of the batch will mix everything together; you get only an average. I would batch stones passed at one time. Analyse individually stones passed at different times because things change.

General measures can help prevent recurrence in people who have formed only one calcium stone

Although people believe that high fluid intake will reduce stone formation, a detailed review of the literature found only one reliable trial to support that belief.

This figure from that one trial shows that formation of a new stone was delayed by high water intake in patients who had formed a single stone. After just one stone nearly 30% of people who did not increase their urine volume (Group 2, average 1 liter daily) had formed at least one more by 5 years whereas only 10% of those with a higher fluid intake (Group 2, 2.6 liters daily) did so.

As expected urine supersaturation fell with higher volume – 2.6 vs. 9.9 and 0.48 vs. 1.58, treated vs. controls, CaOx and CaP SS respectively. A fall of supersaturation would reduce the free energy of crystal formation and that could explain the fall in new stone formation.

But it is hard to do everything with just fluids. The day is long and various. We sleep by night. People forget. Crystals never sleep. Crystals never forget. In a trial, with prompting from nurses, people will maintain a high urine flow, but how about the usual situation? You want fluids. But you also want whatever treatment aims most precisely at the crystals you form. That means you need to know what those crystals are. And to find out what the crystals are the stones must be analysed.

Crystal specific treatment is far better than general measures for patients with more than one calcium stone

The patients in the water trial had formed only one stone each, so far as could be told, and only 25% of those who did not raise their urine volumes (Group 2) had another stone in five years. Among people who have formed at least several stones, 60% in the control groups of trials that tested specific treatments formed at least one more stone within 3 years. By contrast only 15 – 20% of those receiving specific treatments formed another stone during the same interval. These control patients all raised their urine volumes. None had average volumes so low as the 1 liter/day in the control group for this trial.

High water intake may well be ideal for those who have formed only one stone, but the large numbers of patients who have formed more than one stone will predictably form more stones at much higher rates and benefit greatly from treatments that focus on their specific stone crystal.

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28 Responses to “WHAT KIDNEY STONES ARE”

  1. Michael Connell

    Hello Dr. Coe,
    I am a PA in a urology practice. I have a patient , a woman , 47yo. Most recent CT scan shows numerous stones in both kidneys. And yet her 24 hour urine results while not quite perfect are as follows: urine vol = 2.76L ; SS CaOx =1.25; urine Ca = 70 ; Oxalate = 25; citrate = 758; SS CaP = 0.18; pH = 5.975; SS UA = 0.44; UA = 0.565; urine Na = 175; P24 = 0.960. Her stones are CaOx monohydrate. What am I not seeing ?

    Michael Connell

    • Fredric Coe, MD

      Hi Michael, Her present urine would not have produced stones. I suspect in her history you will find periods in which urine chemistries would have been most abnormal. Regards, Fred

  2. jagat

    hi,, Dr.
    which madison is better for kidney stones,
    i have booths kidny stone(less Than 5.5mm)
    & i take more madison also .

  3. Liege Jung


    I have a history of calculi in both kidneys, first diagnosed at age 19, lithotripsy on the right kidney at age 21 after evaluation of a calcium oxalate stone that passed, a few infections treated in the next few years and no more trouble for over a decade. No trouble meant I more or less forgot about diet and fluid intake and now at age 38 my last tomography shows numerous stones in both kidneys, all small and dense – the largest in the upper third of the left kidney is 5 x 4 mm 1200 UH, all others are smaller than 4mm.

    My urologist says nothing can be done except drink a lot of water and new exams every year to control. I am looking for another specialist and came to your very informative website. I was surprised to learn a higher calcium intake is recommended. I haven`t noticed other stones passing so I am not sure if it is possible to evaluate their formation. What are other recommendations?

    Thank you!

  4. Edward Quinton

    I have produced a stone first on the right kidney early this year that is soft in nature, and so big it won’t pass. through the tube. I’m a 60 year old male with prior history of stones. Nor any prior family history. It formed and then shut the tube off. Two days later my kidney shut down and by then I had gone septic from infection. Then three months later the left side did the same thing. Back to the hospital for treatment for blood infection for a week of antibiotics. Both times I went to surgery for a stint to open up the tube and allow urine to flow so they could treat the blood infection and then once the Infection is cleared up then they go back in and laser the stone, bust it up , and put in a second stint for a week or so to allow kidney to function normal then pull it. This are very soft, crumbley material. I have been drinking water with a large amount of lemon juice in it for about 8 years now and wondered if it could be related to what is going on

    • Fredric Coe, MD

      Hi Edward, Of highest importance, what is the stone material made of? I would worry it is struvite or uric acid. You need urgent means to prevent more, as sepsis is horribly dangerous. Regards, Fred Coe

  5. Theresa

    Hi Dr. Coe,
    I am a chronic former of calcium oxalate stones. In late 2015, I had shockwave therapy twice to breakup a 10mm stone in the UPJ left kidney. Just recently, I had laser lithotripsy to remove a 5mm stone near the bladder, a 1cm stone in the UPJ, and a 1.2cm staghorn stone at the bottom of my right kidney (along w/multiple stones of smaller sizes). My CT scans shows I have multiple stones of 4mm or less in my left kidney. Between these procedures, I’ve passed multiple smaller stones. What causes people like myself to develop so many stones so frequently and what can be done to stop the formation? I’m on a low oxalate diet, try to consume water to make 2L of urine per day (very hard to do), and take potassium citrate (540 mg).
    Thank you..

  6. Rob Portkins

    Dr. Coe
    I was diagnosed with stones on Tuesday. I am on blood thinner (Effient) Started bleeding in urine last night.
    Hopefullt the stone is moving
    just now a black piece came out into strainer but it seems a little soft so I am thinking it is coagulated blood.
    How do I know if tht was stone?
    I have been 9 months on thinner and am supposed to go 1 year.
    Should I get off or will bleeding stop?


    • Fredric Coe, MD

      Hi Rob, blood thinners and stones and bleeding is a complicated situation. If you think you passed a stone, get it analysed to find out. If you are bleeding clots can feel just like stones – so are you sure there are stones and that they are the cause of bleeding. This is one for your urologist who needs to ascertain the cause of the bleeding. Right now that is the problem. I am afraid that I cannot add much from here. Regards, Fred Coe

      • Rob

        Hello Dr Coe
        The 5 mm stone has moved to the “sphincter” just before the bladder
        the pain is tolerable. I went off the blood thinners but am back on. How long can/should I wait for it to pass and any tips how to get it that last 1/4 inch into the bladder?
        I do not look forward to laser etc.. NYTimes did an article that says big chance of a problem
        thanks in advance

        • Fredric Coe, MD

          Hi Rob, You can wait so long as the kidney is not obstructed. This is a situation in which your personal surgeon is the only person who can make an intelligent decision. Boston, as I said in my personal email to you, is filled with excellent physicians, so I am very confident. Regards, Fred Coe

  7. Marion (female)36

    Dear Dr. Coe,
    It’s been a month after my sugery,
    as per result sent to US it says that my stone type is
    100% Carbonate Dahllite Apatite
    I have read your article but couldn’t find exact answer.
    Looking forward.


  8. Nihal

    Dear Dr. Coe.

    Are most kidney stones somehow attached to the wall of the kidney? If so is it quite a strong bond?

    In my mind, I would think they must be attached, since if the stones are unattached and floating, most stones would come out through the ureter, while they are still small (i.e. they wouldn’t sit there and grow bigger).

    Also what are the densities of the stones compared to the density of urine? I would imagine that the stone density is higher than that of urine. Does that mean that if a stone has formed in a location that is lower than the opening to the ureter, such a stone would never come out on its own, and would just sink to the bottom of the kidney? (this would only be true if stones are not attached to the wall of the kidney)


    • Fredric Coe, MD

      Hi Nihil, Here is a video on how stones form. Crystal densities are higher than water. The urinary tract contracts, so gravity plays little role. Regards, Fred Coe

      • Nihal

        Dear Dr. Coe,

        That was a very informative video. Thanks!.. I still have a couple of questions.

        So from the video, I learned that the stones are attached to the kidney wall (I saw the mark left on the kidney wall left by the surgeon after stone removal in the video). I would think that that implies a considerable force is needed (a force equivalent to the force needed to break the stone) to dislodge the stone. But we know that people pass stones on their own all the time. So how do stones dislodge on their own? Is excessive movement such as running enough to dislodge a stone from the kidney wall?

        Also you said above “the urinary tract contracts”. Does that mean that the kidney contracts every so often to squeeze the urine out of the kidney?


        • Fredric Coe, MD

          Hi Nihal, The tissues separate the stone from its base – the cells are alive. The urinary tract is the renal pelvis and ureter, not the kidney. Regards, Fred Coe

  9. sanjeev mehta

    Please gibe me details of clinical significance of stone analysis, especially Calcium oxalate stones. Also suggest where I can get full details. Thanks
    Sanjeev Mehta

  10. Trish McClain

    Dr. Coe

    People are wanting to know what can you do about cystine stones? Some stoners are making a lot of them and having lots of procedures. They are tired of being sick.



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