Know Your Numbers
Why Do You Need a 24-Hour Urine Test for Kidney Stones?
By Jill Harris, LPN, CHC
Kidney stone prevention nurse since 1998
Updated
Jill’s answer
A 24-hour urine collection is the only way to find out why you are making kidney stones. It shows whether your urine volume is too low, your calcium or oxalate too high, your citrate too low, and more. Ask your doctor to order one after your first stone, and don’t wait for a second.
- Help with your results: schedule a urine analysis consult
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Why Does the 24-Hour Urine Test Matter?
The test tells your doctor how saturated your urine is with stone-forming crystals, and the more saturated it is, the more likely you are to form new stones. Your results will show diet issues and other medical conditions that could be the culprit, and they’re often things you’d never expect.
Too many people make a stone, get scared and start cutting out foods left and right without ever knowing the real problem. They stop eating regular meals, throw out perfectly fine foods, add things they don’t need (like lemons) to everything, and follow advice from anybody with a pulse and a Facebook account. That’s how people end up eating five foods while still making stones.
Different urine problems need different solutions. What helps one person may not help you, and that is exactly why this test matters so much.
It lets us stop guessing.
Jill Harris, LPN, CHC
When Should You Ask for One?
Ask after your first stone. Many doctors don’t order a collection at first and say, “Let’s just wait for the second episode before testing.” I do not agree with this approach! Why wait for a second stone, and maybe another surgery, if we can prevent it? If your doctor says you don’t need it yet, push back.
What to say to your doctor
Be direct. You can say: “I do not want to keep going through this. The urine collection will help show me why I am making stones, and I want that information so I can make the right diet changes.”
That is not being difficult. That is being smart.
Jill Harris, LPN, CHC
For more help asking, read how to ask your doctor for the test.
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What Tests Should Your Doctor Order?
Ideally, the 24-hour urine collection measures:
The 24-hour urine collection 18 values
- Volume
- Calcium
- Creatinine
- Citrate
- Phosphorus
- pH
- Sodium
- Urea nitrogen
- Oxalate
- Chloride
- Ammonium
- Magnesium
- Potassium
- Uric acid
- Sulfate
- Qualitative cystine screen
- Urine collection time
- Supersaturation calculations
Your doctor should also order a fasting blood draw with the collection, though it’s often left off: potassium, chloride, CO2, creatinine, calcium, phosphorus, magnesium and uric acid. If the blood draw isn’t ordered, don’t let that stop you. The urine collection is the most important thing, and you can get the blood test later.
This is the gold standard. Not every lab reports exactly these values, but it should be pretty darn close.
Yes, I like Litholink. I worked there for many years; it was Dr. Coe’s lab, and he sold it to LabCorp. We make no nickels from talking about it. But your doctor doesn’t have to use Litholink. Many doctors are contracted with a specific lab and have no choice. Just get the darn thing ordered, wherever it comes from.
How Do You Do the Collection?
Flush your first morning urine, write down the time, collect everything after that, and then collect the final urine at that same time the next morning.
This is where people often get mixed up. Your collection doesn’t start with a middle-of-the-night bathroom trip. It starts when you wake up and begin your day. That first morning urine was made overnight, before the collection began, so it gets flushed, but the time you urinate is your official start time. The final urine the next morning is saved because it was made during the 24 hours you’re measuring. Once you understand that, the jug may still annoy you, but at least it won’t confuse you.
- Follow your own lab’s instructions.Different labs have different containers, preservatives, timing rules, and ways they want the sample stored or returned. Don’t ask other patients online how to do yours; I see this all the time in Facebook groups, including mine, and their answer may be wrong for your lab. That can throw off your test or get your collection rejected, and then you’ve done all that work to hear, “Sorry, start over.” Read the instructions that came with your kit before you start and follow them exactly. If anything is unclear, call the lab.
- Keep it cool.Most kits explain how to store the urine, and many recommend keeping the container cool.
- Use the hat.If your kit includes a smaller collection device, called a “hat” by us nurses, use it and pour the urine into the larger container. It makes the whole thing much easier.
- Don’t miss a sample.Forgetting even one bathroom trip can throw the whole picture off. Pick a day you can realistically manage. If bathroom breaks are hard to come by at work, plan ahead or choose a better day.
What Should You Eat and Drink During the Collection?
Eat and drink the way you normally do. Choose a normal day for you: not a vacation, not a holiday, not the day you suddenly decide to become the healthiest person in America. Don’t drink extra water or eat perfectly for a day or two to make the numbers look better.
Pretty numbers are not the goal. Honest numbers are.
Jill Harris, LPN, CHC
If it’s your first collection, eat and drink the way you did before you knew you were making stones. You want to see how that old way of eating changed your urine chemistry. Don’t worry; you won’t make a new stone in a single day. They take time to form. If you do change how you eat for the collection, tell your doctor, so they understand why your results look so good.
For follow-up collections, eat and drink the way you do on your treatment plan, and be honest. If you haven’t lowered your sodium to where it needs to be yet, do the collection that way.
If your doctor orders a 48-hour collection
Let those two days reflect real life too. If you can, make one look like a workday and the other like a day off, because many of us eat and drink very differently depending on the day.
What Happens After You Get Your Results?
Your results tell us where to start. Maybe your biggest problem is low urine volume, and hydration comes first. Maybe your urine calcium is high, and sodium is playing a big role. Maybe oxalate is high, and we need to look at what you eat every day. Maybe your calcium intake is too low, and that’s making things worse. Either way, we’re no longer guessing from internet fear or random food lists.
Make sure you understand what your results mean. If your doctor recommends a medication, ask why, and ask whether you can keep working on diet changes first to see if you can avoid it. Sometimes medication is necessary to keep stones away, but you should know what it does and how it affects your condition.
Why Follow-Up Collections Matter
Follow-up collections show whether your treatment plan is working, so please do them. Doctors don’t always remind you. I can’t tell you how many patients come to me with no follow-ups who keep making stones.
The goal is no more stones.
Jill Harris, LPN, CHC
Do a follow-up collection after you’ve made your changes, to see if your changes are having the desired effect, and then do one every year. Your doctor most likely won’t remind you.
Help Understanding Your Results
If your results are sitting in your portal and you’re thinking, what the heck does this mean, you’re not alone. They’re very complicated to read. I have been helping people understand urine collection results since 1998, and I can help you understand your numbers and what to ask next, so you have a better visit with your doctor.
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The 24-Hour Urine Test in All Access: once you know your numbers, the weekly meal plans, my video course and the group calls with me help you work on the goals your results point to.
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Podcast Episodes on the 24-Hour Urine Test
43 episodes of the Kidney Stone Diet Podcast, each with a full transcript. Pick the question closest to yours.
Getting the test and reading your results 15 episodes
- 3 things you need to know before a 24 hour urine collectionEp. 201 · Most searched
- The one thing kidney stone doctors get wrongEp. 304 ·
- What do these lab results mean?Ep. 300 ·
- What does a urine test show for kidney stones?Ep. 278 ·
- Don’t skip this if you want to prevent kidney stonesEp. 266 ·
- “Is my doctor lying to me?”Ep. 242 ·
- Here’s what nobody talks about when preventing kidney stonesEp. 233 ·
- When do I need to see a nephrologist for kidney stones?Ep. 203 ·
- Do I need annual urine collections?Ep. 148 ·
- What is the best prevention for kidney stones?Ep. 110 ·
- How to eat when you have too much oxalate in your urineEp. 69 ·
- Why do I have kidney stones when my urine test results found low to no oxalate?Ep. 40 ·
- Should I get a blood test if I’m a kidney stone former?Ep. 29 ·
- Why am I urinating less?Ep. 16 ·
- Why you need a 24-hour urine collectionEp. 9 ·
High urine calcium, citrate and pH 8 episodes
- The TRUTH about potassium citrate and your kidney stonesEp. 218 · Most searched
- You have no idea this is causing your kidney stonesEp. 305 ·
- The Kidney Stone TRUTH about Apple Cider VinegarEp. 299 ·
- The SECRET about Potassium CitrateEp. 296 ·
- The hidden reason you keep making stonesEp. 293 ·
- Urine pH and kidney stonesEp. 139 ·
- High urine calcium and kidney stonesEp. 94 ·
- Does potassium citrate prevent future kidney stones?Ep. 6 ·
Stone types and conditions that raise your risk 10 episodes
- MSK (Medullary Sponge Kidney) and Kidney StonesEp. 112 · Most searched
- Should you have your kidney stone analyzed?Ep. 180 ·
- Does menopause cause kidney stones?Ep. 147 ·
- Bariatric Patients and SupplementsEp. 130 ·
- How fast do kidney stones form?Ep. 118 ·
- Diabetes, low carb, and uric acid stonesEp. 105 ·
- I have one kidney. How do I prevent kidney stones?Ep. 59 ·
- How can diabetics avoid kidney stones?Ep. 43 ·
- Does weight loss surgery increase kidney stone risk?Ep. 34 ·
- What can I eat?! I produce uric acid and calcium oxalate kidney stones!Ep. 14 ·
Medications, supplements and remedies 10 episodes
- Does Ozempic cause kidney stones?Ep. 206 · Most searched
- Most people don’t know this about collagenEp. 267 ·
- Can too much vitamin C lead to kidney stones?Ep. 245 ·
- Can I do the Kidney Stone Diet if I’m on medication?Ep. 202 ·
- Does biotin cause kidney stones?Ep. 162 ·
- Is fish oil good for kidney stones?Ep. 156 ·
- 5 natural remedies to fight kidney stonesEp. 151 ·
- Does Glucosamine cause kidney stones?Ep. 106 ·
- Which vitamins are hard on kidneys?Ep. 76 ·
- Are supplements safe for kidney stone formers?Ep. 10 ·
Go Deeper
- How to Eat During a 24-Hour Urine CollectionWhat your eating and drinking should look like on collection day.
- 24-Hour Urine Analysis ConsultWork with me to understand your results before your doctor’s visit.
- How to Ask Your Doctor for the TestWhat to say to get a collection ordered.
- What Is the Kidney Stone Diet?The guidelines to follow for your follow-up collections.
- 24-Hour Urine Collections Are Not AvoidableDr. Coe’s article on why the test matters.
Frequently Asked Questions
What does a 24-hour urine test show?
A 24-hour urine collection is the only way to find out why you are making kidney stones. It shows whether your urine volume is too low, your calcium or oxalate too high, your citrate too low, and more.
Do I save the first morning urine?
No. Flush it and write down the time; that’s your start time. Save the urine at that same time the next morning, because it was made during the collection.
Should I drink more water before my test?
No. Eat and drink the way you normally do, so the results show what’s really driving your stone risk.
Does my doctor have to use Litholink?
No. Many doctors are contracted with a specific lab. Just get the test ordered, wherever it comes from.
What if my doctor doesn’t order the fasting blood draw?
Do the urine collection anyway. It’s the most important part, and you can get the blood test later.
What if my doctor says to wait for a second stone?
Push back and ask for the test now. There’s no reason to wait for another stone, and perhaps another surgery.
What if I miss a sample?
Missing even one bathroom trip can throw the whole picture off. Follow your own lab’s instructions exactly, and if anything is unclear, call the lab and ask them directly.
How often should I do a 24-hour urine collection?
Do a follow-up collection after you’ve made your changes, to see if your changes are having the desired effect, and then do one every year. Your doctor most likely won’t remind you.
Why is the urine collected in one jug instead of testing each sample?
To get an accurate look at your day, you need to collect it for the entire day. Separate samples would show moment-to-moment ups and downs, but that is not what this test is validated for. Urine changes a lot with meals, fluids, sweating, exercise and time of day, so testing each pee separately would add a lot of noise and make the results harder to interpret. In stone prevention, the reference ranges and treatment decisions are based on the full 24-hour collection, not a series of spot samples.
Why do I keep making stones when my 24-hour urine results are normal?
If your labs are perfectly normal, you would NOT be making stones. Many people are told their results are normal, but the lab’s reference ranges may not represent stone former risk; they can be a more lenient value that could still lead to stones. If your doctor doesn’t know where a stone former’s values should be, that could be the problem.
How long after kidney stone surgery should I wait to do a 24-hour urine test?
It depends on how your recovery is going. If you are eating and drinking normally, you can do it. I would wait 3 to 4 weeks.
Is it too late for a 24-hour urine test if I already changed my diet?
It’s never too late to ask for the test. It shows whether your diet changes have helped and your stone risk looks low, and I would highly advise it to prevent further stones.
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Six evidence-based goals
Kidney Stone Diet Goals
Your results tell us where to start.
Goal 1
Goal 2
Goal 3
Goal 4
Goal 5
Goal 6
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About Jill Harris, LPN, CHC
Jill Harris is a Licensed Practical Nurse (LPN) who specializes in kidney stone prevention, with more than 26 years of experience and years of work with University of Chicago nephrologist Dr. Fred Coe. Her goal is to teach you what you need to know and, more importantly, how to put that knowledge to work so you can stop forming stones. More about Jill