IMG_2303Jeff, a reader of this site, suggested this topic and I realized it was one that I should have written long ago.

You can make sense of all those numbers in the 24 hour kidney stone reports.

You can use those numbers to understand how things stand with you.

Reading the numbers can help you achieve your best possible chance at stone prevention – which is the only reason all those lab tests were done in the first place.

This article deals with calcium stones. A second one will cover uric acid stones.

Be Sure You Have Been Screened For Systemic Diseases

Your physician does this part. But even for systemic diseases stone risk is gauged in the urine so you can read along and assess how prevention is going.

Units of 24 hour Urine Measurements


Because excretions of stone risk factors are in amount per 24 hours, we need the time of the collection. You provide the beginning and end times for the collection, in minutes and hours, and the laboratory corrects all excretion values to amounts in 24 hours.

For example, you start a urine collection at 7 am and complete it at 5 am the next morning. The measured total time is 22 hours. If the volume is 1.5 liters, the volume ‘corrected’ to 24 hours is 1.5 liters x 24 /22 (1.09) or 1.636 liters/24 hours.

It is obvious that the less ‘correcting’ the better, because the ‘correction’ assumes that every hour is the same as every other hour, which is not likely. So you want to collect as close to 24 hours as possible. If your time is below 22 or above 26 hours throw it away – no cost – and do another.

I am sure this is an unnecessary comment but sometimes people forget that a urine collection begins by emptying the bladder, writing down the time, and discarding the urine. Here and there people add it, making the real collection from whenever the bladder had last been emptied.

Volume per 24 Hours

Urine volume is measured in liters (L) or milliliters (ml). A milliliter is 1/1,000 of a liter, so there are 1,000 ml in a liter. One liter is 1.06 quarts. The laboratory measures the total volume of urine if you send or bring it. Often you will read the volume yourself, off of a collection container.

Because excretion rates like calcium, oxalate, citrate, and uric acid are calculated by multiplying their concentrations by the 24 hour volume, mistakes in timing, collection, or measurement of volume will make the results less valid. You provide the collection times, assure all the urine has been collected, and even may measure the volume, so quality is under your control.

Excretion Rates

Urine creatinine, calcium, oxalate, phosphate, and citrate excretions, are in milligrams (mg) or grams (gm) per 24 hours. A mg is 1/1,000 of a gram. An ounce contains 28.3 gm.

Urine sodium is measured in millimoles (mmol) or milliequivalents (mEq)/24 hours. Atoms, like sodium, each have a weight made up mainly of their constituent protons and neutrons. One mmol of sodium is 23 mg.

Some atoms like calcium have two charged sites which can bind to other molecules or atoms. They are often measured in milliequivalents (mEq) which is the weight times the number of sites. Sodium has only one, so mmol and mEq are the same.

Molecules like creatinine and oxalate have weights made up of their constituent atoms.

Conversion of Units

Some laboratories report in mmol or mEq. You can convert your lab report if it differs from mine. I will be using L for urine volume, mg for urine creatinine, calcium, oxalate, and citrate, and mmol for urine sodium. Here are the conversions:

Creatinine; 113 mg/mmol

Calcium: 40 mg/mmol; 20 mg/mEq

Sodium: 23 mg/mmol or mEq

Oxalate (oxalic acid): 88 mg/mmol; 44 mg/mEq

Citrate (citric acid): 189 mg/mmol

Direct Measurements

Acidity or alkalinity are measured in pH – no units. It is a logarithm to the base 10 so a change from 6 to 5 means a 10 fold increase in acidity, from 6 to 7 a ten fold increase in alkalinity.

Supersaturations are calculated from urine concentrations. The one we use here is the ratio of the concentration dissolved in urine of each of the three important stone forming salts, calcium oxalate, calcium phosphate, and uric acid divided by their individual solubilities at body temperature. Values below 1 mean crystals will dissolve. Values at one mean crystals will neither grow nor shrink nor form. Values above 1 mean crystals can form and grow. Being a ratio it has no units.

Is The 24 Hour Urine Valid?

Urine creatinine

Like all 24 hour excretion rates, that for creatinine is calculated from the concentration, measured volume, and collection time.

Because muscle cells make almost all the creatinine lost in urine any two urines you collect will have about the same amount of creatinine in them. A more than 20% variation between two urines suggests an error in one collection. If there are many collections, most creatinine excretions will line up pretty well, and an outlier – too high or low by more than 20% of the average for all the collections will stand out.

When a urine stands out as different from prior collections, I say it is best to repeat it. If there are two, use the one that seems more correct.

‘More correct’ is judged by expected amounts of urine creatinine. For men, one expects about 18 – 24 mg/kg body weight; for women, 16 – 22. A urine far out of those ranges is suspect. In people who have a high body fat percentage the ratio can be as low as 12 mg/kg/day, and people who have little body fat and a high muscle mass can be as high as 30 mg/kg/day.

Conditions of Collection

Did you eat and drink as usual, or show off? Had you ‘improved things’ since a recent stone so your collections reflect new habits and not those that led to the stones? Every collection is a one day frame out of a movie that is running 365 frames a year, so if these few days do not reliably represent your average life, their results will inevitably mislead you and your physicians and falsify what you came to do.

Reading the Results

Urine Volume

Curhan and colleagues have linked new onset of stones to urine volume in three large cohorts reviewed in our other articles. Take a look now. The graph is on page 2 of the article. Risk is on the vertical axis, and urine volume is on the horizontal axis. When red shows above the line at 1 it is above normal.

Risk is low above 2.25 liters/24 hours. But the day is long and the 24 hour urine is an average, so for insurance it is best to overshoot so the low times are still not too low. I would say 2.5 – 3 liters liters/24 hours is ideal.

Urine Calcium

Stone risk increases with urine calcium excretion above 200 mg/day in men and women – take a look. The calcium risk is at the upper left corner of the graph.

If you have above 200 mg/24 hours you have ‘hypercalciuria’, a high enough calcium to pose risk of stones – and also bone disease. There are many causes of hypercalciuriaThe commonest is simply a genetic tendency, called idiopathic hypercalciuria. ‘Idiopathic’ means your physician has ruled out any of the other causes of hypercalciuria.

You lower urine calcium in idiopathic hypercalciuria with reduced diet sodium, avoidance of sugar loads, and medications if needed. You compare treated to untreated excretion to see how well the treatment worked.

Urine Sodium

Urine sodium is essentially the diet sodium intake. Because urine losses can lag intake when intake varies sharply, urine sodium is a good estimate of the average over 3 – 4 days. If you tried to lower your diet sodium to 100 mmol/24 hours, 2,300 mg intake, and you find 200 mmol/24 hours, you can be sure that your average intake is on average twice what you desired.

Suppose your urine calcium is 250 mg/24 hours, urine sodium 200 mmol/24 hours – twice the upper limit of diet sodium in the US and above the optimal value of 65 mmol (about 1,500 mg/24 hours). You would want to lower your diet sodium. Suppose your urine sodium was already 65 mmol/24 hours and urine calcium was 250 mg/24 hours; you would want to take other steps like thiazide diuretics or potassium citrate.

What if your urine calcium is 450 mg and your urine sodium is 200 mmol? Sounds like a bigger problem, but it is not. When urine calcium is higher the slope dependency of urine calcium on urine sodium is steeper, so the same reduction of sodium could bring urine calcium quite a way down.

If you lowered diet sodium and there is no change, do not assume the test is wrong. Check the creatinine values – do they match? If so, you have not lowered your average sodium intake. Sodium is an atom and you are not a cyclotron; you cannot make sodium or destroy it.

Sugar Loads

Given to people with idiopathic hypercalciuria they cause a rapid rise in urine calcium and supersaturation. The 24 hour urine will tend to underestimate this because of averaging throughout the day.

Thiazide Diuretics and Potassium Citrate

These drugs come after diet changes have not proven sufficient and are added to the diet changes.

Urine Oxalate

Stone risk increases with increasing urine oxalate and if the risk ratio is not as high as for calcium risk appears at very low levels of excretion – above 25 mg/day. In general, high urine oxalate comes from high oxalate diets, low calcium diets, or the combination of high oxalate and low calcium together. Therefore treatment is dietary. Excellent food lists are in this site – linked from the oxalate diet article. Rarely, urine oxalate is raised from a hereditary overproduction state – primary hyperoxaluria. Likewise, bowel diseases can raise urine oxalate. These are complex conditions and diet alone is rarely enough.

If urine oxalate is high and you have corrected both your diet oxalate intake and added significant diet calcium, you may have some form of genetic or acquired oxalate overproduction or an otherwise inapparent intestinal absorption problem.

Urine Citrate

Citrate is a powerful force against calcium stones. It binds calcium in a soluble complex. It interferes with calcium crystal formation and growth. Low urine citrate is a risk factor for new stone onset – bottom left panel of the graph. Above 400 mg daily there is no extra risk of stones in men or women, so ‘hypocitraturia’ means a urine citrate below 400 mg daily.

If you begin taking, as an example, four 10 mEq potassium citrate pills a day – 40 mEq, that extra 40 mEq of potassium should appear in the urine. If it is not there, the pills may not be delivering the medication into the blood from the bowel. The urine pH should rise because citrate imposes an alkali load. If it does not and the urine potassium does rise, you may need more of the medication.

Urine ammonia – I will cover this in the second half of this two part article – is a major way the body removes acid, so when you take citrate ammonia excretion should fall. If it does not fall, and urine potassium rises perhaps your pills are potassium chloride – the pharmacist switched from what was prescribed.

Strangely, the urine citrate itself does not rise in everyone even when potassium and pH rise and ammonia falls.

Urine pH

A low value – below 5.5 poses a risk of uric acid stones. A high value, above 6.2 raises calcium phosphate supersaturation and risk of calcium phosphate stones. Potassium citrate can raise urine pH; there are no medications to lower urine pH except methionine and ammonium chloride and these are not usable for stone prevention because they will increase urine calcium and pose a risk of bone mineral loss.

Urine Supersaturations

Get Them

If there are no supersaturations, ask that your samples be processed by a vendor that provides them. Supersaturation is the driving force for crystal formation and growth, and invaluable for monitoring stone prevention.

Relate Them To Your Stone Crystals

There will be three supersaturations: Calcium oxalate, calcium phosphate, and uric acid. Inspect the ones related to your stone crystals. For calcium oxalate both calcium oxalate and calcium phosphate supersaturations matter. If calcium phosphate, that one matters most. If pure uric acid, it is uric acid supersaturation.

Reduce Them

One should not compare values in a stone former to values in normal people, who often have urine supersaturations as high or higher than those of stone formers. Active stone formation means supersaturation is too high for you whatever the value may be and needs to be lower. You reduce your supersaturations by increasing urine volume and reducing excretions of calcium and oxalate, or raising excretion of citrate without undue increase of urine pH. That is why we make these measurements.

Compare Then to Now

Compare you now to you before your most recent fluid and diet intakes or medications: If they have fallen, things are going well; if they have risen things are not going well. If stones are still forming, supersaturations need to be lower. If there have been no more stones and supersaturations are stable, stand pat. If supersaturations are below 1 and stones are still forming, the urine samples do not properly represent your real life.

A Good Schedule

When? I like two 24 hour urines before treatment – it gives a sense of averages. After treatment has begun – diet changes, fluid goals, lifestyle, it is important to get another. The timing is up to patients: You know when something has changed, or ought to have changed, and need to be sure it has indeed changed in the right direction. It goes on like that until treatment is reaching its goals – lowering supersaturation by at least half – after which once a year is a good idea.


308 Responses to “HOW TO READ YOUR KIDNEY STONE LAB REPORT – Calcium stones”

  1. Brett Besag

    Hi Dr. Coe,
    Thank you for your website, it has changed my life! I am 5’7”, 135lb, semi-athletic, 55-year old male, who has had nine confirmed kidney stones in my life, the first at the age of 19. Four stones have required surgeries, one via SWL and three (including two in May) via lithotripsy. My stone in 2018 and one of the two in May were analyzed as Calcium Oxalate Dihydrate (Weddellite) 15%, Calcium Oxalate Monohydrate (Whewellite) 70%, Carbonate Apatite (Dahllite) 15%, and two previous stones 10+ years ago were also Calcium Oxalate.

    In 2018, I increased my water intake to 4-liters/day mixed with 1/2 cup of lemon juice, but was probably ingesting ~3,000mg sodium, < 500mg of calcium/day, and eating a lot of spinach, etc. Not surprisingly, I still ended up with two large stones 3 years later. In May, I discovered your site and have been following a 700-1,000mg sodium, 950-1,100mg calcium and 125-200mg oxalate per day diet since May. As a result of this new diet my chronic hypertension is almost completely gone (reducing Enalapril from 40mg to 2.5mg / day).

    I completed my first ever 24-hour analysis last week, with blood work done the next day. My results are below. In consultation with my GP and urologist, I am switching my HBP medication from Enalapril to two 12.5mg Hydrochlorothiazide/day, in the hopes that the HCL will both control my hypertension and lower my urine calcium. I will do a 2nd 24-hour collection in January.

    My questions for you are: Should I be concerned re: my urine pH and SS CaP? Do I need to reduce my oxalate intake? Do you believe I have reduced my sodium too much, since my urine sodium is so low? Am I semi-unique in that my urine sodium is <36 but my urine calcium is still 290? I definitely am an outlier on your urine calcium vs urine sodium chart! 🙁

    Thank you again for providing such valuable data and insight to all of us!

    Urine Volume: 3.65
    SS CaOx: 3.73
    Urine Calcium: 290
    Urine Oxalate: 31
    Urine Citrate: 579
    SS CaP: 1.74
    24 hour Urine pH: 6.962
    SS Uric Acid: 0.04
    Urine Uric Acid: 0.456
    Na 24: <36
    K 24: 103
    Mg 24: 129
    P 24: 0.847
    Nh4 24: 23
    Ci 24: <55
    Sul 24: 39
    UUN 24: 9.01
    PCR: 1.1

    Normalized Values:
    Cr 24: 1420
    Cr 24/Kg: 22.8
    Ca 24/Kg: 4.7
    Ca 24/Cr 24: 204

    Metabolic blood test results:
    Sodium: 139
    Potassium: 3.9
    Calcium: 9.0
    Creatinine: 0.95
    Bun/Creatinine: 14.7

    • Fredric L Coe, MD

      Hi Brett, What a great outcome! Lowering diet sodium really does lower BP and the switch to a thiazide is smart in that it will lower urine calcium and replace the pril. With such a low diet sodium and high a water intake, adding thiazide might lower serum sodium, so your physician better check at one week and one month to be sure. I might start with a lower dose of the thiazide, perhaps 12.5 daily – and follow home BP – more predictive than office measurements. I do not think you have lowered diet sodium too much – over 3 liters of urine, lower limit of sodium is partly low intake and partly dilution so we do not really know your total daily sodium loss. But if it were 40 mEq/day, in 3.65 liters of urine, its concentration would be too low to measure Regards, Fred Coe

      • Brett Besag

        Ty Dr. Coe! Yes, sorry for the duplicate entry, I wasn’t sure if my original went through. To keep my BP under control, it’s looking like I will be on 25mg of Hydrochlorothiazide, twice a day (my BP was too high on 12.5mg x2). As for follow-up blood work, that is definitely happening. I am excited that I’ll be down to one medication that will hopefully take care of both my hypertension and hypercalciuria.

        Is there anything else I should be doing, for instance, should I be concerned re: my urine pH and SS CaP, or since I don’t have a history of Calcium-Phosphate stones, I should be ok in that regard? Thank you again!

        • Fredric L Coe, MD

          Hi Brett, You want SS CaP below 1, but the pill may achieve that. Chlorthalidone 12.5 mg/d does lower urine pH – we published that – so if the OHCTZ does not achieve a low SS CaP perhaps the CTD will. Low diet sodium is important so use 24 hour urine testing to know what it is. Fred

      • Brett Besag

        Hi Dr. Coe. I’m having some difficulties with some HCTZ side-effects, the worse being that my tinnitus seems to be worse. I’ve moved up my next 24-urine test to be middle of September (ie, 6 weeks after starting the HCTZ), to see if the HCTZ lowered my urine calcium, so I’ll stay on the HCTZ till after the results are in. My question for you is, with my urine calcium at 290, sodium < 36, and oxalate at 31, how likely is it for me to get more CO stones, if I end up not taking a thiazide (all thiazides seem to exacerbate tinnitus)? Maybe my tinnitus will subside with time, but hasn't so far. 🙁 Sorry for all the questions.

        • Fredric L Coe, MD

          Hi Brett, The best risk assay is the SS for CaOx and CaP; if you can get the former under 3 and the latter under 1 you are pretty safe. Without thiazide, your best BP drug is a sartan – I like Losartan. Be sure and follow home BP as these are most predictive of outcomes. Fred

          • Brett Besag

            Funny you mention a sartan! My GP and I have found the correct BP balance for me with the Losartan 50mg / 12.5 HCTZ pill. Hopefully it will help my urine calcium level.

            Currently & for the past 3 years, I drink 1/2 cup of lemon juice concentrate mixed with a ~gallon of water / day. I assume the lemon juice is improving my citrate, but is it also contributing to my urine Ph? Should I cut back on it a bit, or leave it well enough alone? Thanks as always!

            • Fredric L Coe, MD

              Hi Brett, As I do not really know the details of your medical situation, I should refrain from too much intervention that might be a disservice. For example the exact balance between citrate and pH response to a citrate load require one see the whole picture – that is your physician. Fred

              • Brett Besag

                I understand. My last last question, if you are willing… How is it possible that my urinary sodium is so low (<36) while my urine calcium is still so high (290)? I am concerned that my Intermittent Fasting, in which I ingest ~500mg of calcium twice/day, but only separated by ~4.5 hours is causing (at least in part) my high urinary calcium. Do you believe that is possible? Would it be better to be ingesting ~350mg of calcium via three meals, each separated by ~4 hours?

                I've read NIH articles, etc, and I can't find any clear statement, other than non-cited declarations that ingesting too much calcium at one meal causes elevated urinary calcium levels, which I am not sure is true or not! 🙁

              • Fredric L Coe, MD

                Hi Brett, I have presumed you take your calcium as food. Supplements without food is not a good idea. If you must use supplements take them with your larger meals to assure a slower absorption. The problem I alluded to in a prior note is haunting us here. I do not know the details of your stone disease or your life in general, so as I am pushed to provide more detailed advice errors can easily occur. If you want me to provide detailed advice, I do telemedicine and can provide exactly what one would want, at the expense of considerable time and effort for us both. In a public forum, where I am rather ignorant of details, I fear misleading you. Regards, Fred

        • Fredric L Coe, MD

          Hi Brett, There is no basis for estimating. Thiazide lowered stones by about 50% vs. nothing in trials but there are no trials of thiazide vs. low sodium diet. Fred

  2. Cameron B Besag

    Hi Dr. Coe. I’ve had 9 stones in my life (from 18 to 55 years old). 4 have been tested, and all were Calcium Oxalate Dihydrate (Weddellite) 15%, Calcium Oxalate Monohydrate (Whewellite) 70%, Carbonate Apatite (Dahllite) 15%.

    3 years ago I increased my water intake to 4 liters / day, mixed with 1/2 cup of lemon juice concentrate, but continued a diet medium-high in sodium, low calcium, and high oxalate. In May, I ended up with 2 more 9mm stones (one of which was analyzed as listed above). I then found your site (thank you!) and significantly reduced my sodium intake to ~800-1,000mg / day, calcium ~= 1,000, and ceased eating the super high oxalate (I used to eat a LOT of spinach). I’ve been on this new diet for 3 months now.

    My first ever 24/hour urine test just came back from Litholink, and I seem to be a bit unlucky. My urine sodium is wonderfully low, my oxalate is almost ok, but my urine calcium is still relatively high, especially considering how low my sodium is. Considering I don’t get a TON of stones, are my current results good enough, or do I need to do more? For instance, my oxalate intake is ~175mg / day.

    Urine Volume: 3.65
    SS CaOx: 3.73
    Urine Calcium: 290
    Urine Oxalate: 31
    Urine Citrate: 579
    SS CaP: 1.74
    24 hour Urine pH: 6.962
    SS Uric Acid: 0.04
    Urine Uric Acid: 0.456
    Na 24: <36
    K 24: 103
    Mg 24: 129
    P 24: 0.847
    Nh4 24: 23
    Ci 24: <55
    Sul 24: 39
    UUN 24: 9.01
    PCR: 1.1

    Normalized Values:
    Cr 24: 1420
    Cr 24/Kg: 22.8
    Ca 24/Kg: 4.7
    Ca 24/Cr 24: 204

    I also had a CBC and Metabolic blood work done, though 1 day later.
    Blood sodium: 139
    Potassium: 3.9
    Creatinine: 0.95
    Bun/Creatinine: 14.7
    These values are consistent with the past 5+ years of annual blood work.

    Thoughts? TIA!!!!

    • Cameron B Besag

      I should have included my Serum Calcium: 9.0.

    • Fredric L Coe, MD

      Hi Cameron, I believe I already discussed these values for you with a first name Brett – I recognized the urine sodium and calcium. Fred

  3. Brenda Gaudette

    My urine sodium was 125 and My report said Treat with diet sodium 2300-3500 mg/day

    • Fredric L Coe, MD

      Hi Brenda, The tolerable upper limit for diet sodium – urine sodium is diet sodium on average – is 100 mEq which is 2300 mg/d. Thence the note. Fred

      • Brenda Gaudette

        So if I’m understanding you correctly I should be consuming no more than 2300 mg/ sodium daily?

        • Fredric L Coe, MD

          Hi Brenda, 2300 mg of sodium is the ‘tolerable upper limit’ of sodium for the US population, so yes. Fred

  4. Melinda

    I’ve had multiple stones mostly when I’ve been pregnant. I have 3 children. I do take potassium cit, citrate 10ml 2 times a day but honestly I always forget at night.
    Stone risk factor
    Vol: 1.27
    SS CaOx: 8.24
    Ca 24: 222
    Ox 24: 31
    Cit 24: 528
    SS CaP: 4.66
    Ph: 7.1
    SS UA: 0.10
    Ua 24: 0.779
    Dietary factors
    Na 24: 161
    K 24: 71
    Mg 24: 88
    P24: 0.896
    Nh4 24: 19
    Cl 24: 121
    Sul 24: 45
    UUN 24: 11.90
    PCR: 1.4
    Normalized values
    Cr 24: 1361
    Cr 24 kg: 22.7
    Ca 24 kg: 3.7
    Ca 24/ cr 24 163

    • Fredric L Coe, MD

      Hi Melinda, The fact that most catches my eye is the remarkably low urine volume. So low that stone prevention is impossible. How about more than double? Three liters a day would perhaps be all you need for prevention. The potassium citrate is raising your urine pH and risk for CaP stones, and even with it your citrate is not all that high – 525. Not sure if it is good or not for prevention – something your physician has to figure out. Regards, Fred Coe

  5. snair

    Hi Dr. Coe,
    Thank you for your time. Here’s my 48Hr Litholink report. I had CaOx stones, 49yr, 133lb, exercise 5 days a week. The Day2 collection volume was lower, likely due to it being a day I exercised. The Na 24 was higher on Day2 due to electrolyte consumption I am guessing.
    Since both ph and citrate are low, am I a good candidate for Potassium Citrate supplementation? I have since increased my water intake.

    Collection Day 1:
    Urine Volume – 2.68
    SS CaOx (liters/day) – 5.90
    Urine Calcium (mg/day) – 372
    Urine Oxalate (mg/day) – 35
    Urine Citrate (mg/day) – 291
    24 Hour Urine pH – 5.288
    SS CaP – 0.25
    SS Uric Acid – 1.22
    Urine Uric Acid (g/day) – 0.544

    Collection Day 2:
    Urine Volume – 2.15
    SS CaOx (liters/day) – 7.01
    Urine Calcium (mg/day) – 350
    Urine Oxalate (mg/day) – 34
    Urine Citrate (mg/day) – 360
    24 Hour Urine pH – 5.426
    SS CaP – 0.24
    SS Uric Acid – 1.24
    Urine Uric Acid (g/day) – 0.525

    Dietary Factors – Day1, Day2 values (comma separated)
    Na 24 – 94, 144
    K 24 – 35, 45
    Mg 24 – 196, 168
    P 24 – 0.971, 0.756
    Nh4 24 – 54, 42
    Cl 24 – 107, 161
    Sul 24 – 53, 47
    UUN 24 – 11.93, 9.91
    PCR – 1.5, 1.2

  6. Lea

    Hi Dr. Coe!
    I am currently going through the process to donate one of my kidneys. On my initial visit, a microscopic urinalysis showed a moderate value for Calcium Oxalate Crystals. It was recommended that I complete a 24-hour stone analysis. I am a 41 year old female and do not have a history of stones. It was thought I may have had one 6 years ago, but if I did I was able to pass without knowing it. Below are the results of the 24-hour stone analysis:
    Urine Volume: 1.84L
    SS CaOx: 6.99
    Urine Calcium: 175mg
    Urine Oxalate: 31mg
    Urine Citrate: 1037mg
    SS CaP: 1.13
    24 Hour Urine PH: 6.478
    SS Uric Acid: 0.16
    Urine Uric Acid: 0.377g

    The transplant team recommended I go over the results with my PC. My PC suggested that I discontinue the prenatal vitamins and other supplements, and be mindful of foods that are high in calcium and vitamin C. I made the changes (also increased my average water consumption to 2.5-3L perday) and repeated the 24-hour stone analysis 90-days after the initial test. Below are those results:
    Urine Volume: 1.82L
    SS CaOx: 8.01
    Urine Calcium: 381mg
    Urine Oxalate: 26mg
    Urine Citrate: 1306mg
    SS CaP: 1.29
    24 Hour Urine PH: 5.864
    SS Uric Acid: 0.76
    Urine Uric Acid: 0.527g

    Needless to say, my numbers did not go in the direction I was anticipating. The transplant team has now recommended that I meet with their kidney stone clinic, but am unable to get in until the end of October. Are you able to provide any recommendations?

    Any tips are greatly appreciated!


    • Fredric L Coe, MD

      Hi Lea, assuming your blood calcium is normal you have idiopathic – genetic – hypercalciuria. Urine calcium is very responsive to diet sodium, and I imagine that went up between the two collections. If I were asked, I would not encourage donation as your urine calcium is quite high, you made obvious crystals and will have only one kidney. Low calcium diet with IH is not good for bones, and bone disease is well described. Likewise, I noticed a very high urine citrate despite a rather low urine pH in the second collection – perhaps your nephrologists might want to ponder that in terms of other health risk factors such as blood lipids, blood pressure, and blood glucose to be sure there are not problems there – I am an outsider, so this is mere suggestions to the wise. Regards, Fred Coe

  7. Brent

    Good Day Dr Coe,
    My recent Litholink is very good except for 2 metrics. (My previous Litholink was in Dec 2020):
    Mg24 was 182 dropped to 51. Since 2016 the range has been 116 – 182 so this is puzzling.
    pH was 5.813 now is high at 6.877
    I currently take Pot Citrate 15MEQ 2 tabs twice daily and have been on this dosage for the past year. My pH has done this before. In 2019 under the care of a different doc it went up to 6.782 who over-reduced Pot. Citrate. Since we switched doctors I am confident our current doctor can tweak the Pot Citrate dosage, so am not too concerned about this.

    Regarding the drop in Mg24 – I have been taking a Mg supplement as Mg Threonate 3tbs/day each 144mg for the past 4 years – consistent with the prior Litholink. I am also on a thiazide – Indapamide – on a dosage that has been constant for the past 4 years. In fact I have had no Rx changes for the past 1 and 1/2 years.

    I would appreciate any thoughts you might have.

    In case other metrics might suggest a reason here they are:
    Vol 24 – 3.99
    SS CaOx – 0.81
    Ca 24 – 73
    Ox 24 – 28
    Cit 24 – 585
    SS CaP – 0.34
    pH 24 – 6.877
    SS UA – 0.04
    UA 24 – 0.541
    Na 24 – 223
    K 24 – 96
    Mg 24 – 51
    P 24 – 1.006
    Nh4 24 – 14
    Cl 24 – 205
    Sul 24 – 43
    UUN 24 – 11.94
    PCR – 0.9


    • Fredric L Coe, MD

      Hi Brent, thiazide causes magnesium wasting, and you are probably depleted – most magnesium is in cells not blood. Your supplement is too modest – try 400 mf OTC Mg oxide, 1 or 2 a day. Your diet sodium (223 mEq/d) is way too high, a reasonable upper limit is 100 mEq (2300 mg). The high sodium load worsens potassium and magnesium loss. Urine pH rises inevitably with alkali – nothing can be done about it. Your stone risk is low. Regards, Fred Coe

  8. Brenda Gaudette

    These are the results from my 24 hour urine collection.
    Urine Volume 2.35
    SS CaOx 6.79
    Urine Calcium 303
    Urine Oxalate 31
    Urine Citrate 540
    SS CaP 0.41
    24 Hour Urine ph 5.608
    SS Uric Acid 0.85
    Urine Uric Acid 0.503
    My stones are Calcium Oxalate
    Monohydrate 15%
    Dihydrate 80%
    Hydroxyapatite 5%
    I am currently drinking 3 liters of water per day, eating close to 1200 mg of Calcium rich foods, getting up to 1500 mg of sodium and eating under 25 mg of added sugar daily. Is there anything else I should be doing?

    • Fredric L Coe, MD

      Hi Brenda, You are pretty typical of a woman calcium oxalate stone former. Your urine calcium is high enough to pose risk of more stones, and you did not post your urine sodium – is it really 65 mE1 (1500 mg)? If not, get it to be. If that fails, thiazide would be the next step. Regards, Fred Coe

  9. Cynthia

    Dr. Coe,
    I recently had my first kidney stone (around 7mm), which I passed about 2 weeks after diagnosis. My brother and multiple family members also have a history of kidney stones. The urologist sent my stone for analysis, had me complete a 24 hour urine and referred me to renal clinic (I also have a history of vesicoureteral reflux as a child on the side where the stone was located). CT at the time I presented with kidney stone to the ER showed moderately severe hydronephrosis and the urology fellow on call mentioned that my renal parenchyma was low on that side but he didn’t seem super concerned about it (my mother has since told me that my left kidney was noted to be smaller than the right when I was worked up as a child). The results of stone analysis and 24 hour urine are below. I realize that I need to drink more water which I will start to focus on but wondering any other recs based on this profile. I won’t be seen in the renal clinic until early Sept. but would like to start making any recommended modifications. I also have a diagnosis of ulcerative colitis. I am in my mid 40s, around 5’1″ and around 105 pounds.

    COMPONENT 1 (CALCULUS): Calcium Oxalate Dihydrate (Weddellite) 30%
    Calcium Oxalate Monohydrate (Whewellite) 35%
    Carbonate Apatite (Dahllite) 35%

    24 hr Urine:
    CALCIUM, URINE 195 mg/day
    SODIUM URINE 141 mEq/day
    POTASSIUM, URINE 33 mEq/day
    PHOSPHORUS, URINE 689 mg/day
    MAGNESIUM, URINE 51 Low mg/day
    SULFATE URINE 10 mmol/day
    BRUSHITE 3.55 High
    SODIUM URATE 2.25 High
    URORISK OXALATE 19 mg/day
    URORISK URIC ACID 386 mg/day
    URINE CITRATE 630 mg/day
    Low urine volume
    Brushite (Ca phosphate)
    Monosodium urate

    • Fredric L Coe, MD

      Dear Cynthia, Your urine is very alkaline – pH 6.8 and you seem to have a high supersaturation with respect to brushite – your stone is 35% calcium phosphate. The low volume is an obvious problem that you can fix out of hand. Your urine calcium is hefty, just below overt increase in stone risk, and in part this is due to your high diet sodium (140 mEq in the urine is the diet intake) so you might want to moderate that to 1500 mg (65 mEq) daily. The stone formed in an injured kidney (smaller) and the urine from that kidney may be even more alkaline, moreover the drainage from that side may be abnormal fostering stones. That is about all I can do to help you without actually knowing your medical condition. Regards, Fred Coe

  10. Jay

    Thank you for your awesome site and resources. After suffering stones for a while, my Dr finally after bugging, sent me for a stone analysis and 24 urine collection. Here are my results.

    Stone type: Calcium Oxalate Dihydrate / Calcium Phosphate mixed

    I did 3 days of urine testing (way it’s done in my Province, 1 jug is no additive, 1 has HCL, 1 has NAOH) My volumes for the 3 days were 2.3L, 3.6L, 2.6L

    Creatinine 7.1 mmol/L
    Urate 1.5 mmol/L
    Creatinine 5.8 mmol/L (day 2 jug)
    Oxalate 115 umol/L
    Creatinine 4.4 mmol/L (day 3 jug)
    Magnesium 1.5 mmol/L
    Calcium 1.76 mmol/L

    I still have to go for blood work, but at least after a year of suffering, I have the ball rolling. I currently have 13 stones between both kidneys, ranging from 3mm to 13mm. I’m making them frequently, so I’m hoping these urine results can shed some light on what’s going on.
    Phosphate 6.95 mmol/L (THIS IS MARKED AS LOW VALUE)
    Citrate 1.25 mmol/L


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