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How to Test For Oxalate: 24 Hour Urine Test For Kidney Stones

Although collecting your urine for 24 hours isn’t the most glamorous task, the information you get from this test is invaluable. Plus, it is a whole lot better than needles in my opinion! A 24-hour urine test will test for oxalate and many other minerals and factors that impact your risk for kidney stones.

Learn more about this test for oxalate and other kidney stone urine risk factors.

Why To Test For Oxalate

Testing for oxalate is important for people who have had kidney stones. A 24 hour urine test will test for oxalate, and other important urine risk factors for kidney stones like urine volume, calcium and citrate levels.

Your doctor may also test for oxalate and kidney stone risk if have Crohn’s disease or have had bariatric surgery or other type of intestinal surgery. All of these conditions can change how your body absorbs oxalate and put you at higher risk of kidney stones.

Risks of High Oxalate Levels

The biggest risk of high oxalate is kidney stones. High levels of urine oxalate increase your risk for the most common type of kidney stone, calcium oxalate.

Some animal studies have shown that oxalate crystals can cause faster progression of Autosomal Dominant Polycystic Kidney Disease. (1)

Rare Complications of High Oxalate Levels

In extreme situations, high oxalate can cause kidney damage. However, these complications usually only happen with a history of Roux-en-y gastric bypass surgery, excessive vitamin C supplementation, or a rare genetic condition called primary hyperoxaluria. (2) (3)

Some cases of kidney damage have been reported with extraordinarily high oxalate intakes. But, in all cases, oxalate foods were being consumed in very high concentrations such as in supplements or smoothies. (4) (5)

If kidney damage is severe, this can cause kidney failure. If oxalate levels remain high in kidney failure, oxalate can build up in the blood. This is a condition called oxalosis. Oxalosis can cause arthritis, bone disease, anemia, skin ulcers and heart and eye problems.

Risks of Low Oxalate Levels

Oxalate itself doesn’t have a function for humans. Therefore, there are no risks of low oxalate levels.

3 Ways to Test For Oxalate

There are a few ways your doctor can test for oxalate. Let’s walk through the 3 common oxalate tests.

24 Hour Urine Oxalate Test

The most common way to test for oxalate is with a 24-hour urine oxalate test. This test measures the amount of oxalate in your urine for an entire day.

A 24-hour urine oxalate test is the best way to know if you need to limit how much oxalate you eat. If your urine oxalate is not high, oxalate is likely not the cause of your kidney stones and you do not need to limit high oxalate foods.

To complete a 24-hour urine test, you need to collect your urine for a 24-hour period. Your doctor will give you exact instructions about when to start and stop your urine collection. You may need to add a preservative to the collection. Different labs have different collection protocols, so be sure to follow your instructions carefully.

There is not an official definition of a “high” level for oxalate on a 24-hour urine test. But, an oxalate level over 40mg of oxalate per day should be addressed. Keep reading to learn how to lower oxalate levels.

A 24-hour urine test will give you the most complete picture of the cause of kidney stones. Oxalate is only one possible cause. See below for other important things a 24-hour urine test will measure.

If you’ve never had a 24-hour urine test for oxalate, ask your doctor today! Stand up for your health. You deserve the BEST kidney stone care.
Click here for talking points to ask your doctor for a 24-hour urine test!

Or, click here to have the talking points sent straight to your inbox!
Infographic of the 3 ways to test for oxalate. A 24 hour urine test (provides the most information about how to prevent kidney stones), a kidney stone analysis (tests the composition of the compounds your stone is made of. Gives some direction for treatment) and a blood oxalate test (rarely used. only provides information about oxalate, not other kidney stone risk factors.)

Kidney Stone Composition Analysis

You can test for oxalate by analyzing your kidney stone itself. It is important to know what kind of kidney stone you have, because medical and nutrition treatment is different for different kinds of kidney stones.

To get your kidney stone analyzed, you usually simply need to give your stone to your doctor. If you pass a kidney stone at home, try to catch it with a screen or fine mesh colander. If it passes at the hospital or doctor’s office, make sure your medical team sends it to be analyzed. If you have surgery to remove a kidney stone, confirm your doctor will analyze the stone fragments.

Chances are, your kidney stone is made from many different compounds. It is rare, for example, for a kidney stone to be 100% calcium oxalate.

Blood Oxalate Test

A blood oxalate test is less common. This test doesn’t check other kidney stone risks, so it doesn’t give a comprehensive picture of why kidney stones are forming.

This test is most commonly ordered for the rare genetic condition, primary hyperoxaluria. It could also be used for people who have had bowel surgery or are being evaluated for a kidney transplant.

A normal blood oxalate level is <2.0 mcmol/L. (6)

How Much Is An Oxalate Test?

The cost of your oxalate test depends on your insurance coverage. I recommend checking with your insurance before you schedule an oxalate tests to make sure it is affordable. Alternatively, you can work with the finance department at your doctor’s office to help you determine coverage.

In most cases, the oxalate test will be covered by your insurance if you have a history of kidney stones or hyperoxaluria.

Beyond Oxalate: Other Important Pieces Of A 24-Hour Urine Test

A 24-hour urine test will measure much more than oxalate. Oxalate is only a (relatively small!) piece of the puzzle when it comes to kidney stone prevention.

Urine Volume

Goal: At least 2 1/2 liters

Urine volume is perhaps the most important thing you can change to reduce kidney stones. The higher your urine volume, the less concentrated the minerals in your urine are. This equates to a lower risk of kidney stones!

For kidney stone prevention, a urine volume of at least 2 1/2 liters per day is recommended. (7)

Urine Calcium (Ca)

Goal: Less than 200mg (women) or less than 250mg (men)

High urine calcium (or, hypercalciuria) is the most common cause of kidney stones. If urine calcium is high, your doctor will probably check to make sure you do not have hyperparathyroidism, sarcoidosis or other causes of hypercalciuria.

Counterintuitively, people who have high urine calcium do not need to limit how much calcium they eat. Instead, it is important to eat enough calcium from food for kidney stone prevention. (7) (8)

To lower urine calcium, your doctor may prescribe a thiazide diuretic. Limiting sodium to 2,300mg per day and avoiding too much added sugar and protein can also reduce urine calcium levels. (8)

Urine Citrate

Goal: At least 550mg (women) or 450mg (men)

Low urine citrate levels cause kidney stones. Citrate makes it harder for kidney stones to form. (9)

If you have low urine citrate, your doctor may prescribe potassium citrate. You can also increase urine citrate levels by eating plenty of fruits and vegetables and avoiding large amounts of protein. (9)

Citrate supplements, such as Litholyte* and Moonstone* are also available. Ask your doctor if these supplements are right for you. In some cases, these supplements could increase urine pH too much.

Urine pH

Goal: 5.8 – 6.2

Urine pH is a measure of acid levels in your urine. Low urine pH means there is too much acid. High urine pH means there is not enough acid.

Most people have a urine pH that is too low (or, they have too much acid in their urine). Low urine pH is a risk factor for uric acid kidney stones, and (to a lesser extent) calcium oxalate kidney stones. (7)

To increase urine pH, make sure to eat plenty of fruits and vegetables. Aim for at least 5 servings each day. Too much protein can lower urine pH, so avoid too much animal protein.

Urine Sodium (Na)

Goal: 100mEq (translates to eating 2,300mg of sodium)

The amount of sodium in a 24-hour urine test is almost an exact measurement of the amount of sodium you eat. Because eating too much salt puts you at risk of kidney stones, this is a great way to check in and see how much salt you are eating. For many people, this can be eye opening!

Sodium on 24-hour urine tests is usually given in milliequivalents (mEq). Use this equation to figure out how many milligrams of sodium you are eating:

Sodium intake (milligrams) = 24-hour urine sodium (mEq) x 23

Remember, most people should eat no more than 2,300mg of sodium per day for kidney stone prevention.

Urine Urea Nitrogen (UUN)

Goal: Varies

Urine urea nitrogen is an estimate of how much protein you eat. This is important because too much protein can lower urine pH and citrate. Excess protein can also increase urine calcium and possibly oxalate. (7)

To use UUN to see how much protein you are eating, use this equation:

Protein intake (grams) = [(Body weight in kilograms x 0.031) + UUN in grams] x 6.25

Supersaturation Calculations

Goals: Calcium Oxalate <4, Calcium Phosphate <1, Uric Acid <1

You may have a value for the “supersaturation” for calcium oxalate (SSCaOx), calcium phosphate (SSCaP) and uric acid (SSUA) on your 24-hour urine test results. Think of these as a “risk score” for the chance of forming that kind of kidney stone.

Supersaturation is determined by all the things in the 24-hour urine test that impact risk for that particular kind of kidney stone.

Where Does Oxalate Come From?

Oxalate that shows up on oxalate tests comes from two primary sources: what your body makes (aka the liver), and what you eat.

Oxalate From Your Liver

Your liver can make oxalate from certain compounds including some sugars, ascorbic acid (aka vitamin C!) and some proteins. (10)

The oxalate your liver makes accounts for a large amount of the oxalate in your body! Up to 50% of the oxalate in your urine can come from oxalate liver production. (10)

Oxalate From Your Food

Oxalate also comes from the food you eat. However, dietary oxalate only accounts for 10-50% of the oxalate in your urine. (10) (11)

How to Lower Oxalate Test Levels

It may surprise you that the best way to lower urine oxalate levels is not necessarily to cut oxalate out of your diet.

Here are some things you can do to lower oxalate levels if your oxalate test is high.

Eat Enough Calcium

Counterintuitively, it is important for people with calcium oxalate kidney stones to eat enough calcium. Calcium binds to oxalate in the intestines, and reduces how much oxalate gets absorbed. (12)

Eating enough calcium tends to be the most effective way to lower oxalate.

Aim to eat 1,000-1,200mg of calcium per day. A goal of 3 servings of calcium-rich foods per day will meat this calcium goal. Dairy tends to be the best source of calcium. But, some dairy substitutes can also be good sources of calcium for kidney stones. (7)

Importantly, calcium supplements can add to kidney stone risk, whereas calcium in food reduces risk. (13)

Infographic of the 5 Steps to lower oxalate. 1) Eat enough calcium. 2) Limit added sugar. 3) Limit non-dairy animal protein. 4) Limit very high oxalate foods. 5) Avoid vitamin C supplements.

Avoid Too Much Protein & Added Sugar

Because your liver can make oxalate from some proteins and sugars, it is a good idea to make sure you eat the right amount of these nutrients. (10)

Most people should aim for a total protein intake of 0.8-1.0 grams per kilogram body weight per day. However, protein needs vary widely. Ask your dietitian how much protein is right for you.

The American Heart Association recommends no more than 25 grams of added sugar per day for women, and 36g for men.

Importantly, fruit does not contain added sugar. For most people, fruit should not be limited because fruit tends to help stop kidney stones. (14)

Oxalate Foods

If your urine oxalate is high, you should stay away from a few foods that are very high in oxalate. Here are foods that are very high in oxalate:

  • Spinach & chard
  • Almonds
  • Beets
  • Rhubarb
  • Raspberries
  • Navy Beans

Get my full oxalate list here!

Remember, the 24-hour urine oxalate test determines the right amount of oxalate for you. (7) If oxalate is still high despite getting in enough calcium, you may need to limit oxalate further. For most people, consuming enough calcium is enough to bring down oxalate levels to a safe range.

Work with your dietitian to figure out how much oxalate is right for you!

Avoid Vitamin C Supplements

Your liver is very good at making oxalate from vitamin C. Avoid any supplement, cough drop, vitamin or supplemented food that has vitamin C in it. (7) (10)

Look out for “ascorbic acid” – this is just a fancy word for vitamin C.

How Often Should I Re-Test For Oxalate?

Most people with kidney stones will need more than one 24-hour urine oxalate test. How often you need to re-test depends on many factors. If most things on the test look good, you may just need to re-test every 1-2 years.

However, if you make changes to your medications or diet, it makes sense to test more often. Oxalate tests and 24-hour urine tests will change almost immediately after medication or diet changes are made. However, I recommend re-testing after 2-3 months to make sure your diet is sustainable.

More Help With Kidney Stone Prevention & Oxalate

I know that this kidney stone stuff can be complicated and overwhelming. If you’d like more help learning with kidney stone prevention, check out these resources I’ve put together to help you stop those stones for good!

Online Course: Kidney Stone Nutrition School

My signature 6-week online course is a deep dive into your oxalate test and 24 hour urine results. You will have a crystal clear picture of where to focus your kidney stone prevention efforts. At the end of the course, you’ll know exactly what you should eat, and how your food can help stop those stones.

The course includes recorded lessons (so you can listen whenever it works for you!) along with worksheets, recipes and example meal plans to help you apply what you learn right away!

If you join during a live launch, you’ll also have small group calls with me and other students! This is an invaluable time to ask questions and learn from me and your fellow students!

Kidney Stone Diet Guide

My Kidney Stone Diet Guide is a deeper dive into your 24-hour urine test. It includes step by step instructions to help you identify your kidney stone risk factors, and how to target them with the food on your plate!

Kidney Stone eCookbooks

Image of the winter and summer edition of Stop Kidney Stones From Your Kitchen

For many people, getting in enough calcium to lower oxalate on a 24-hour urine test can be a struggle. So, I created two eCookbooks that are filled with recipes that sneak in that calcium. Recipes are also low in sodium, added sugar, protein and oxalate to check all your possible kidney stone nutrition boxes!

Oxalate & Kidney Stone Articles

As always, you can read up on everything kidney stones and nutrition right here on my site! Check out my personal favorite articles:

Happy Eating!


30 thoughts on “How to Test For Oxalate: 24 Hour Urine Test For Kidney Stones”

  1. Please tell me if eggs are non animal protein? They are not animal flesh and bones but they certainly NOT vegetables! Thank you. I do hope eggs are not verboten because a cheese and vegetable omelette is such an enjoyable non meat entree.

    1. Melanie Betz MS, RD, CSR, FAND

      Hi Carol! Eggs definitely count as “non-dairy animal protein”, but do function somewhere in the middle in terms of plant vs. animal protein. Please remember that meat is ABSOLUTELY NOT “off limits” (unless you want to follow a vegetarian diet). This post goes into this in more detail!

  2. I have incontenance and this makes it impossible to get an accurate result on the 24 hour urine test; the actual amount of volume is 1.2 liters max., sometimes only 1 liter, because the rest of it is absorbed in pads I use while sleeping. Do you have any advice for getting an accurate result? Thanks very much.

    1. Melanie Betz MS, RD, CSR, FAND

      This is a tough one! I’d probably say just collect wheat you can. Your doctor might ask you to weigh the pads to help us get an idea of how much liquid you are missing collecting.

  3. Hi Melanie, and thanks for all this great information. I have a question about my sodium level found during a 24 hr urine test recently. My test results list a ‘normal range’ of sodium as 26.4-243.8 mEq/24 hrs. My result was 28 mEq. You say the amount of sodium in a 24-hour urine test is almost an exact measurement of the amount of sodium you eat and to use a factor of 23 to figure this out. So, I come up with 644 mg of sodium. I also have seen where you have said we should get 1500mg sodium per day minimum. 644 does seem like a very low number but again, the test results indicate it is within, although at the low end, the ‘normal range’. To further muddy the waters, I had annual blood work done within a few weeks of the 24 hr urine test and had a sodium level result of 142mg and the ‘normal range’ on this test is indicated to be 136mg – 145mg. I focused on eating my normal diet at both testing times. I had a calcium oxylate stone removed recently and all other results were in the normal range except urine output, which I am working on dutifully. Do you have any thoughts on this sodium issue?

    1. Melanie Betz MS, RD, CSR, FAND

      Hi Fran! Yes – you calculated your sodium intake correctly and that is quite low. I would a) make sure that was a completely collection and b) think back to if you were eating normally during the time of that test. I would also probably do another one and make sure you get similar results. If so, you do have room to eat a bit more sodium. The amount of sodium in your blood is NOT AT ALL reflective of your sodium intake – so that doesn’t really matter.

    2. Hi Melanie: Thank you for such valuable information. I have been trying my best to find out as much as I can on having higher than usual oxalate level and hiw to orevent the inevitable kidney stones. I was wondering if Tropicana Light orange juice is acceptable. I have been feeling worse after drinking it but not knowing if there is any correlation to the other bad symptoms I feel. thank you so much and yiu are really needed for all of the patients out there guessing on how to navigate this new health concern that kind of came out of nowhere. CH

      1. Melanie Betz MS, RD, CSR, FAND

        Hello! I don’t recommend any fruit juice for people with kidney stones as it tends to increase stone risk. Ultimately, you really need a 24 hour urine test to know WHY you are causing stones – then work with a dietitian to understand exactly which targeted changes you can make to prevent kidney stones for you!

  4. We use freeze-dried acerola cherry powder, amla/gooseberry & camu camu berry for our daily Vitamin C. Does the liver convert these to oxalates?
    We do not take any ascorbic acid Vitamin C.

    1. Melanie Betz MS, RD, CSR, FAND

      Technically any vitamin C could be converted to oxalate. However, it is really only supplemental form we get concerned about.

  5. Hi. My urine calcium was the only high value on my 24 hour test, it was 347. My blood calcium is normal, not sure if that’s relevant here… The nephrologist said keep my calcium intake the same. I do not eat much calcium at all, as i eat no dairy of any kind. I I maybe get some Calcium from veggies and also what’s supplemented in alternative milks, but definitely not a lot nor the daily rec of 1000-1200mg.

    According to my research from you, high urine calcium doesn’t mean stop calcium intake, it means eat MORE calcium? Did i misunderstand?

    Where is the urine calcium coming from then? Leaching from my bones?

    He also said my salt was high even tho the test showed “normal” at 144 mmol. I have been actively reducing that now. He said the urine sodium relates to the calcium?

    1. Melanie Betz MS, RD, CSR, FAND

      Hi Car! All great questions. It sounds like your nephrologist is operating some outdated guidelines in terms of calcium. Here is an article that dives into calcium and stones more. You did not misunderstand. The calcium is likely coming from your bone mass. A 24-hour urine sodium of 144mmol/day equates to consuming 3,312mg sodium/day – about 1,000mg more than what is recommended for people with high urine calcium (or, for general health purposes!). I’m not sure why the “normal” range is so high – MANY urine test companies do this. There are many things we can do nutritionally to help you get that urine calcium down (this is the most common cause of stones). For more help from me, my kidney stone diet guide walks you through this. Or, Kidney Stone Nutrition School is my most comprehensive way for people to learn exactly what and HOW they can make targeted changes for kidney stone prevention.

      1. Thank you! I will keep looking into your recommendations.

        I really don’t eat dairy but i know you said supplemented food can be stone forming, so I’m worried about upping my dairy that way..

        And i have had no added sodium and very little processed food, so Im actually surprised that the sodium was that high! Can something else actually produce higher sodium?

  6. I’m reading your blog with great interest and will be asking my Dr. about the 24-hr urine test. As an ethical vegan on a low acid diet due to reflux but also trying to increase my iron level due to lab-result deficiency, my food world is getting ever more challenging! As I look over the Oxalate food list I don’t see lentils on your helpful table pdf. They’re a mainstay, so I’m wondering about their content/rating. Many, many thanks!

  7. Hi There,

    Is Ascorbic acid which mimics Vitamin C need to be avoided, I have passed a stone they examined it was calcium oxalate and I still have a very small one in addition to a food chemical intolerance so I can’t tolerate Vitamin C but was told Ascorbic acid is not the same as Vitamin C by the dietician but she knew nothing about oxalates !

    1. Melanie Betz MS, RD, CSR, CSG

      Vitamin C is ascorbic acid – same thing! For stones, we don’t want to totally avoid vitamin C. For SOME people with oxalate stones, we want to avoid large doses of supplemental vitamin C!

  8. Be aware that asking your doctor for a 24-hour urine test does not necessarily provide you with a comprehensive report.

    It’s been almost 2 years since I had a large stone removed. After the surgery, my urologist ordered a 24-hour urine test, which the lab called a Stone Risk Profile. It contained almost 20 different measurements. I assume that’s what Melanie means when she uses the term “24-hour urine test.”

    I recently asked my GP to order another one of those tests so I can see if the dietary changes I’ve made have reduced my urine oxalate level. This time, the ONLY results I got was Raw calcium, Timed-urine calcium, Raw creatinine, and Timed-urine creatinine. Now I’ve scheduled an appointment with the urologist, hoping that he will order the correct test…. the one that will tell me the oxalate content of my urine, the pH, and all the other stuff.

  9. Maricor de Guzman

    I tested for 24 hour urine test and my calcium level is 8.77 (high). What do I do? Eat less chicken, pork, beef and less 0% milk?

    1. Melanie Betz MS, RD, CSR, CSG

      How much sodium you eat is the biggest nutrition factor that can influence urine calcium levels. You actually definitely DO NOT want to be on a low calcium diet. I help people fully understand everything they can do to reduce calcium in Kidney Stone Nutrition School! I’ve love to help you.

    1. Melanie Betz MS, RD, CSR, CSG

      Good question! And yes. As long as the patient doesn’t have a reason for a fluid restriction, such as liver failure or congestive heart failure.

    1. Melanie Betz MS, RD, CSR, CSG

      Hi Ferree! This test is actually used for ALL stone types. You would follow similar advice, based on those results, to prevent calcium phosphate stones as well.

  10. Hi, hoping this question can help me and someone else at the same time. What does it mean if your 24 hour Urine pH is always slightly elevated on a litholink test?

    1. Melanie Betz MS, RD, CSR, CSG

      Chances are if your urine pH is just slightly high, it isn’t a big deal. BUT, this really depends on many factors on your urine test. In general, there isn’t a lot nutrition can do to move a very HIGH urine pH. However, there is a lot we can do to increase urine pH. If you have chronically high pH, I’d recommend focusing on the other urine risk factors that urine test shows to ultimately reduce your risk of kidney stones.

  11. Not mentioned here is that what you eat starting 8 hours prior to taking the 24-hour urine test can significantly change the results. You must eat the foods that you would normally eat that are highest in oxalate. If you have a spinach salad 3 days a week, make sure you have one just before or during the test. Same for beets, almonds, chocolate, soy, and peanuts. Eating a low oxalate diet during the test will give you results showing that a low oxalate diet does not cause a problem for you. You need results showing that your normal diet does not cause problems for you.

    1. Melanie Betz MS, RD, CSR, CSG

      Yep! Most doctors will want you to eat your “normal” diet during the test to get a good picture of what is usually going on. Always double check with your doctor!

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