The 24-Hour Urine Test for Kidney Stones, Explained

Medically reviewed by Prof. Bernard Canaud, MD, PhD, Emeritus Professor of Nephrology, Montpellier University School of Medicine

A 24-hour urine test tells us much more than you might think. By collecting your urine over a full day, we can learn how much urine your kidneys produce and deduce how much you drink, how much calcium and oxalate, sodium and other minerals you excrete, whether you have enough protective citrate to help prevent stones, and how acidic your urine is. Think of it as a snapshot of your body's stone-forming environment. If you've had kidney stones, this simple test can be a real game-changer. It doesn't just tell us that you form stones, it helps us understand why, and more importantly, what we can do to prevent them from coming back.

Let's face it: collecting your urine for 24 hours isn't exactly anyone's idea of fun! You spend an entire day keeping track of every drop, carrying around a collection container, and wondering whether you're doing it right. And yes, you probably have a few questions you might feel a little awkward asking. Don't worry, you're certainly not alone!

The good news? It's much simpler than it sounds. Most mistakes happen because the instructions weren't clear enough, especially when it comes to getting the timing right. And that's exactly why we're here to help.

In this guide, we'll walk you through what the test actually measures, how to collect your urine properly, what those mysterious numbers on your lab report mean, and most importantly, how the results can help you and your medical team prevent future kidney stones.

Key takeaways: the essentials at a glance

• Your urine tells a story: A 24-hour urine test measures the daily output of the substances that drive stone formation: urine volume, calcium, oxalate, citrate, uric acid and pH.
• Drinking enough is your best defense: Urine volume is the single most powerful lever you control; a daily target of around 2.5 liters dilutes the chemistry behind stone formation.
• Understanding why stones form changes everything: The test is part of a metabolic stone evaluation: it finds the cause, so stone prevention can be targeted rather than generic.
• It's about prevention, not detection: A 24-hour urine test won't tell you whether you have a kidney stone. That's what imaging tests, such as ultrasound or CT scans, are for.
• One day may not tell the whole story: Most health professionals ask for two collections on separate days, and your results are added to your medical records to track change over time.

What it is, and what it is not

The idea is simple, even if the process sounds a little unusual! A 24-hour urine test, sometimes called a 24-hour urine collection or a 24-hour urine catch, means saving every drop of urine you produce across one full day (a 24-hour period) and sending it to a lab. The lab measures the total volume and the concentration of a set of substances in it, then works out how much of each your body excreted over the day.

But why collect urine for an entire day instead of just filling a small cup?

Because your urine is constantly changing! Its concentration varies depending on how much you drank, what you've eaten, and even the time of day. A single urine sample gives us a snapshot of what's happening at one particular moment. A 24-hour urine collection provides a much more complete picture, showing how much of each substance your kidneys actually excrete throughout the day.

What the test doesn't do is just as important.

A 24-hour urine test won't tell you whether you currently have a kidney stone or where it might be located. That's the job of imaging tests such as ultrasound or CT scans. Instead, the 24-hour test looks at the chemical environment that makes stones more or less likely to form.

And here's something worth remembering: this isn't a test you pass or fail!

Don't be alarmed if some of your results fall outside the usual reference ranges. That's often exactly what we're looking for. Each abnormal value can provide a valuable clue about why stones are forming and, more importantly, what you and your healthcare team can do to reduce the risk of future stones.

The bottom line? Imaging tells us whether you have a stone. A 24-hour urine test helps us understand why stones form, and how to prevent them from coming back.

Why your urologist and a metabolic stone expert may recommend a 24-hour urine test

Because finding a kidney stone is one thing. Understanding why it formed, and preventing the next one, is another!

Kidney stone prevention is often a team effort. Your urologist plays a key role in diagnosing and treating kidney stones, while a metabolic stone expert, often a nephrologist with expertise in stone disease, helps uncover the underlying reasons why they develop. Working together, these specialists look beyond the stone itself to explore the metabolic, dietary, and physiological factors that may be driving stone formation. And that's exactly where the 24-hour urine test comes in.

Here's something that might surprise you: two people with exactly the same type of kidney stone may need very different approaches. One person may excrete too much calcium in their urine. Another may have too little citrate, a natural substance that helps prevent crystals from forming. A third may simply produce too little urine, making it easier for crystals to develop.

Looking beyond the stone: understanding your personal risk

A 24-hour urine test is an important part of a broader metabolic evaluation aimed at understanding why kidney stones form. This evaluation may also include blood tests, imaging studies such as ultrasound or CT scans, and laboratory analysis of any stones you've passed or had removed. Ideally, your urologist and a metabolic stone specialist work together to put all these pieces of the puzzle together. While the urologist focuses on identifying and treating stones, the metabolic specialist explores the underlying biochemical, dietary, and physiological factors that make them develop. Together, they can design a prevention plan that addresses your specific risks rather than relying on general recommendations (Curhan, 2001).

Why does this matter?

Without a detailed metabolic evaluation, kidney stone prevention often comes down to the same familiar advice: drink more water, eat less salt, and watch your oxalate intake. These recommendations can certainly help, but they're not necessarily enough for everyone. For someone who develops stones repeatedly, understanding the specific cause can make all the difference between general advice and truly personalized prevention.

Who should consider a 24-hour urine test?

The American Urological Association (AUA) recommends offering metabolic testing to people who develop kidney stones repeatedly, as well as to first-time stone formers who have additional risk factors or are interested in understanding their personal risk.

Your healthcare team may particularly recommend testing if you:

• Have already experienced more than one kidney stone episode
• Have a family history of kidney stones
• Have conditions such as gout, inflammatory bowel disease, or chronic diarrhea
• Have undergone bariatric surgery
• Have only one functioning kidney
• Have developed several stones at the same time
• Developed kidney stones during childhood

But here's the good news: you don't need to wait for another stone to take action!

Even if you've experienced only one kidney stone and have no obvious additional risk factors, you can still discuss metabolic testing with your healthcare professional.

Why prevention matters, even after your first stone

Unfortunately, kidney stones have a tendency to come back. Studies show that recurrence is common, although the risk varies widely from person to person. Some long-term estimates suggest that up to half of stone formers may experience recurrence within ten years, depending on the population studied and how recurrence is defined. However, the risk of a second symptomatic stone is generally lower and depends on individual characteristics (Rule et al., 2014).

A special note on children

Collecting urine for 24 hours can be challenging for anyone, but it's especially tricky for young children, particularly those who aren't yet toilet-trained! One study suggested that routine 24-hour urine collection in children experiencing their first kidney stone may be costly, difficult to complete, and may not always lead to changes in treatment (Carnes et al., 2021). However, kidney stones in children deserve special attention, as they may be associated with underlying metabolic or genetic conditions and carry a substantial risk of recurrence. For this reason, a metabolic evaluation remains important, even when a full 24-hour urine collection isn't practical. Alternative approaches, such as spot urine measurements adjusted for age, may provide useful information.

The bottom line?

Whether and how to perform a 24-hour urine collection should be decided with a pediatric nephrologist or urologist experienced in kidney stone disease, taking into account the child's age, medical history, and individual risk factors.

What the test measures

A stone risk panel typically reports somewhere between eight and fifteen values. These are the ones that drive decisions.

Understanding your results: two things that might surprise you

Remember that there's no single perfect number for everyone. Reference ranges may vary between laboratories and depend on factors such as age, sex, and body size. Your laboratory report will usually show its own reference ranges alongside your results. These are useful starting points, but your healthcare team will interpret them in the context of your personal stone risk.

Now, let's look at two findings that often surprise people.

1. Citrate: your body's natural defense against kidney stones

Citrate is something most people have never heard of, yet it plays an important role in protecting your kidneys against stones. Think of citrate as a natural bodyguard. It binds to calcium in your urine, making it harder for crystals to form and grow. Your body obtains citrate from food, particularly fruits and vegetables, but urinary citrate levels depend largely on how your kidneys handle it. One important factor is your body's acid-base balance, which is influenced by diet. For example, diets rich in animal protein may increase acid production and reduce urinary citrate, while fruits and vegetables can have the opposite effect.

The good news? Low urinary citrate is a common and often treatable risk factor for kidney stones. Depending on your results, simple dietary changes or specific oral treatments may help restore this natural protection.

2. Calcium: why eating less isn't always the answer

Here is one of the biggest misconceptions about kidney stones: if you have too much calcium in your urine, you should stop eating calcium-rich foods. Surprisingly, that's usually the wrong approach! Your body needs calcium, and getting enough of it through your diet can actually help prevent the most common type of kidney stone.

Here is why: when you eat calcium-containing foods, calcium binds to oxalate in your intestine, reducing the amount of oxalate absorbed into your bloodstream and eventually excreted in your urine. If you reduce too much dietary calcium intake, more oxalate may be absorbed, potentially increasing your risk of calcium oxalate stones. For most adults who form calcium stones, maintaining a normal dietary calcium intake, typically around 1,000–1,200 mg per day, is preferable to restricting it. Of course, excessive sodium intake and other metabolic factors can increase urinary calcium losses, which is why understanding your complete 24-hour urine profile is so important.

The take-home message? Kidney stone prevention isn't simply about avoiding certain foods. It's about understanding how your body handles minerals and other substances, and finding the right balance for you.

How to collect your urine for 24 hours: a simple step-by-step guide

Collecting your urine for an entire day might sound a little awkward, but don't worry! It's actually quite simple once you understand the routine. Getting it right matters, because even one missed collection can affect your results.

Before you start: a little preparation goes a long way

Your laboratory or clinic will provide a special collection container, usually a large plastic jug, sometimes two, along with instructions.

One important safety point: Some containers already contain a preservative, which may be acidic or potentially harmful. Never empty, rinse, or add anything to the container unless your laboratory specifically tells you to. Keep it safely away from children and pets, and avoid direct contact with any preservative. If necessary, use a separate clean collection cup to transfer urine into the main container.

Choose a convenient day. Ideally pick a day when you will be at home for most of the time. You can certainly collect urine on a working day, but having easy access to your collection container makes life much simpler!

Here is something really important: don't change your usual habits just for the test!

Eat and drink as you normally would, unless your healthcare professional has given you different instructions.

Why? Because the goal is to understand what happens in your everyday life, not what happens when you're suddenly on your best behavior! Drinking three liters of water when you usually drink one, or dramatically cutting back on salt for just one day, might make your results look better. But those results wouldn't reflect your usual habits, and that could lead to less appropriate prevention advice.

The best test is one that reflects the real you!

The 24-hour collection: step by step

Step 1. Start your clock.
When you wake up, go to the bathroom and urinate into the toilet as usual. Don't collect this first urine. Simply write down the exact time. That's when your 24-hour collection begins.

Step 2. Collect every drop.
From that moment on, collect all the urine you produce throughout the day and night. Yes, even if you wake up at 3 a.m.! Every collection counts, so try not to miss any.

Step 3. Store it properly.
Follow your laboratory's storage instructions. Many collections need to be kept refrigerated or in a cooler with ice packs, while others may have different requirements depending on the preservatives used.

Step 4. Finish at exactly the same time the next morning.
Here's the part that sometimes causes confusion. When you wake up the following day, collect your urine at the same time you started the day before. This final sample goes into the container.

Step 5. Return your collection.
Close the container securely and return it to the laboratory as soon as instructed, following the directions provided with your kit.

The golden rule: skip the first, keep the last!

If there's just one thing to remember, it's this: on Day 1, your first morning urine goes into the toilet. On Day 2, your urine at the same time goes into the collection container.

Why the difference?

Because the urine sitting in your bladder when you first wake up was produced before your 24-hour collection began. By emptying your bladder and starting the clock, you're giving yourself a clean starting point. The final collection, exactly 24 hours later, captures the urine produced up to the end of that period.

And that is it! You've collected a full day's worth of information about how your kidneys work.

Five common mistakes that can affect your results

A 24-hour urine collection is simple in principle, but a few small mistakes can make the results less reliable. The good news? Most are easy to avoid once you know what to watch out for!

1. Missing a bathroom visit: Every drop counts! Forgetting to collect even one urination can underestimate the amount of substances your kidneys excrete throughout the day. If you miss a collection or accidentally spill some urine, don't try to make up for it. Simply let your laboratory know. You may need to repeat the test to get accurate results.

2. Collecting the first morning urine: Remember the golden rule: skip the first, collect the rest! Your first morning urine contains substances your kidneys produced before the collection period began. Including it can artificially increase your measured daily urine volume and excretion.

3. Forgetting the final morning urine: This is the other side of the same mistake! The urine you pass exactly 24 hours after starting belongs in the collection container. Leaving it out means you're missing part of the period you're trying to measure.

4. Suddenly changing your eating or drinking habits: Tempted to drink extra water or eat less salt just to get better results? Resist the temptation! For your initial evaluation, the goal is to understand your usual habits. Dramatically changing your diet or fluid intake for the test may produce misleading results and lead to recommendations that don't reflect your everyday needs.

5. Collecting urine when your body isn't back to normal: A urinary tract infection, a recent kidney stone episode, or a urological procedure can temporarily affect your urine chemistry. Whenever possible, metabolic testing should be performed when you're clinically stable, free of active urinary infection, and back to your usual routine.

Why might you need two collections?

You might wonder: "If I've already collected urine for an entire day, why would I need to do it all over again?"

It's a fair question! The answer is simple: your urine chemistry changes from day to day. What you eat, how much you drink, your physical activity, and other factors can all influence the results. That's why guidelines often recommend two 24-hour urine collections, ideally on separate days, especially when evaluating recurrent kidney stone formation. It's not because your first collection was unreliable. It's because two collections can provide a more complete and representative picture of your usual metabolism. That extra information can help your urologist and metabolic stone specialist to develop a more personalized prevention strategy.

Where is your 24-hour urine test analyzed?

Once you've completed your collection, what happens next?

Your urine sample is sent to a specialized laboratory, where it is analyzed to uncover the chemical factors that may be contributing to your kidney stones. In the US, one of the best-known services is Litholink, part of Labcorp, which specializes in kidney stone risk evaluation. The process is straightforward. Your healthcare professional orders the test, and a collection kit is delivered to your home. It includes the necessary containers, instructions, and packaging to return your samples to the laboratory. You'll also be asked to record important information, such as your collection times and, depending on the kit, your total urine volume. Once the laboratory has analyzed your samples, it produces a detailed report showing your urine chemistry, highlighting potential risk factors, and calculating supersaturation, a measure of how likely certain types of kidney stone crystals are to form in your urine.

Think of it as a personalized map of your kidney stone risk!

If you repeat the test later, your healthcare team can compare the results to see whether changes in your diet, fluid intake, or treatment are helping.

Are other laboratories available?

Absolutely! Other providers, including Quest Diagnostics and hospital-based laboratories, offer similar 24-hour urine stone risk evaluations. Most measure the same key substances, such as calcium, oxalate, citrate, uric acid, and sodium. However, laboratories may use different reference ranges, reporting formats, and methods for calculating supersaturation. For this reason, using the same laboratory for follow-up testing can make it easier to compare your results over time.

That said, switching laboratories is perfectly possible. Your healthcare team can interpret the results while taking any methodological differences into account.

What about cost and insurance?

The good news is that many US health insurance plans cover 24-hour urine testing when it is medically indicated, particularly for patients with recurrent kidney stones. However, coverage isn't automatic, and your out-of-pocket costs will depend on your insurance plan, deductible, laboratory network, and the specific tests ordered.

A practical tip: Before starting, check with your insurance provider or laboratory to confirm coverage and find out whether you'll have any additional costs. If you're paying yourself, ask for the full self-pay price in advance. Prices can vary considerably between laboratories.

The bottom line? Wherever your urine is analyzed, what matters most is having a reliable test, understanding what the results mean, and using that information with your urologist and metabolic stone specialist to build a personalized prevention plan.

How to read your 24-hour urine test results

Your laboratory report may look a little intimidating at first. Lots of numbers, unfamiliar names, and values highlighted in red! But don't worry. Once you know what to look for, it becomes much easier to understand. Each measurement usually comes with your result and a reference range or recommended target. And while your urologist and metabolic stone specialist will help you interpret the full picture, here are five simple steps to get started.

1. Start with urine volume: are you drinking enough?

This is often the easiest, and one of the most important, things you can improve. If your daily urine volume is below 2 liters per day, your urine may be too concentrated, making it easier for stone-forming substances to crystallize. Remember, the less urine you produce, the more concentrated calcium, oxalate, uric acid, and other substances may become, even when the total amount your kidneys excrete is normal. For most people who form kidney stones, the goal is to produce at least 2.5 liters of urine each day. That usually means drinking more than 2.5 liters of fluid, since some water is lost through sweating, breathing, and other normal bodily functions. The good news? Increasing fluid intake is one of the simplest and best-supported ways to reduce kidney stone recurrence.

2. Look at supersaturation: how likely are crystals to form?

Your laboratory may calculate separate supersaturation values for calcium oxalate, calcium phosphate, and uric acid stones. These calculations combine several factors, including urine volume, mineral concentrations, pH, and natural inhibitors of crystallization. Higher supersaturation generally means a greater tendency for crystals to form, although it doesn't necessarily mean a stone will develop. One of the most useful things about supersaturation is that it can be followed over time. If your values decrease after dietary changes or treatment, that's often a reassuring sign that your urine chemistry is moving in the right direction.

3. Check the individual measurements: what is driving your risk?

Now it's time to look at the individual substances measured in your urine. Is your calcium too high? Your oxalate elevated? Your citrate too low? Or perhaps your sodium excretion suggests you're eating more salt than you realize? Each abnormal value provides another piece of the puzzle.

Here's something important: you don't need every number to be perfect! Some people have one dominant abnormality, while others have several contributing factors. Your healthcare team will identify which findings matter most for your particular type of kidney stone. The goal isn't simply to bring every number into the laboratory's reference range. It's to identify the factors that are increasing your stone risk and determine which ones can be improved.

4. Don't overlook urine pH: acidity makes a big difference

Urine pH is one of the most informative, and sometimes overlooked, measurements on your report. It tells you whether your urine is acidic or alkaline, and that can make a big difference in the type of stones you're likely to form.

For example:

• Uric acid stones are strongly associated with acidic urine. Raising urine pH through appropriate treatment can help prevent these stones and may even dissolve existing uric acid stones.
• Calcium phosphate stones are more likely to form in alkaline urine. Raising urine pH too much may increase their risk.
• Calcium oxalate stones can form across a relatively broad pH range, so other urinary factors are often more important.

This illustrates an essential principle of kidney stone prevention: a treatment that helps one person may not be appropriate for another. That's why urine pH should always be interpreted alongside stone composition, other urine measurements, and your medical history.

5. Check creatinine: was your collection complete?

Creatinine may seem like just another number, but it serves a different purpose. Your body produces creatinine mainly through muscle metabolism, and your kidneys eliminate it in urine. Over 24 hours, the amount excreted is usually fairly consistent for a given person. This makes urinary creatinine a useful way to assess whether your collection was reasonably complete. If the value is unexpectedly low or high, your healthcare team may wonder whether some urine was missed, the collection lasted too long, or there was another problem. However, an unusual creatinine value doesn't automatically mean your collection was incorrect. Age, sex, muscle mass, protein diet, and kidney function can all influence creatinine excretion. If there is genuine concern about collection completeness, your clinician may recommend repeating the test.

What happens next? Turning numbers into a prevention plan

Here's where all those measurements start to become genuinely useful!

Rather than giving you a long list of restrictions, your urologist and metabolic stone specialist can use your results to identify two or three priorities that matter most for you.

Your personalized prevention plan might include:

• A daily fluid goal to keep your urine sufficiently diluted.
• A sodium intake target to help reduce urinary calcium losses.
• Dietary adjustments, including maintaining adequate calcium intake and reducing excessive oxalate exposure when appropriate.
• Increasing urinary citrate, through dietary measures or medication when indicated.
• Specific medications, such as potassium citrate or thiazide-type diuretics, depending on your metabolic abnormalities and stone composition.

The story doesn't end there. Repeating the 24-hour urine test after implementing your prevention plan allows your healthcare team to see whether those changes are actually working.

Are you producing more urine? Has calcium excretion decreased? Is citrate improving? Has supersaturation fallen? These changes can provide valuable feedback and help fine-tune your treatment over time.

The bottom line? Your 24-hour urine report isn't just a collection of laboratory numbers. It's a practical guide to understanding your personal kidney stone risk, and, together with your healthcare team, turning that knowledge into a plan to prevent the next stone.

What happens between tests? The missing piece in kidney stone prevention

Here's the catch with the 24-hour urine test: it's an excellent tool, but it only gives us a snapshot of a single day. You collect your urine, receive your results, and work with your healthcare team to develop a personalized prevention plan. You may be asked to drink more water, reduce your salt intake, adjust your diet, or take medication to improve your urine chemistry. But then comes the tricky part: what happens during the weeks and months between tests? You go back to your everyday life, trying to follow your new routine. Perhaps you're drinking more water at first, but gradually slip back into old habits. Maybe reducing salt turns out to be harder than expected. Or perhaps your citrate treatment isn't producing the metabolic changes everyone hoped for.

The problem? Without regular feedback, you may not know whether your prevention plan is actually working until your next 24-hour urine collection, often several months later. That can be frustrating for both patients and healthcare professionals.

One day doesn't always tell the whole story

Research highlights two important challenges:

First, 24-hour urine testing remains underused. In a large study involving 130,489 US veterans with kidney stone disease, only 14.8% underwent a 24-hour urine collection. This suggests that many patients may never receive a detailed metabolic assessment to guide personalized prevention (Ganesan et al., 2019).

Second, urine chemistry can change considerably from one day to another. In an analysis of 70,192 paired urine collections, nearly one-third showed differences of 30% or more in urinary calcium excretion or urine volume (Alruwaily et al., 2016).

These findings remind us that a single collection, however useful, may not fully capture the natural variability of our daily lives.

The take-home message?

"A 24-hour collection is the reference standard, and it should stay that way. But it describes one day. What clinicians and patients have never had is what happens on the other three hundred and sixty-four, when the plan is either working or quietly falling apart."

What if kidney stone prevention could move beyond occasional laboratory snapshots toward more regular, personalized feedback, helping patients and clinicians understand not just what should work, but what is actually happening in everyday life?

Tracking between collections: filling the gaps

What if you could learn more about your urine chemistry without waiting months for your next laboratory test?

That's the idea behind U-Scan Calci, a small urine-monitoring device designed to fit inside your toilet bowl and make regular monitoring easier. Instead of collecting urine in a container or visiting a laboratory, you simply activate a measurement through the app. The device analyzes your urine and helps you follow three important indicators over time:

• Urinary calcium: to monitor changes in calcium concentration.
• Urine pH: to understand whether your urine is becoming more acidic or alkaline.
• Hydration status: to help you recognize changes in urine concentration and hydration-related patterns.

With a suggested routine of two measurements per week, U-Scan Calci offers a convenient way to observe how these indicators change during everyday life.

A complement to your 24-hour urine test, not a replacement

Your 24-hour urine collection remains essential for a comprehensive metabolic evaluation. It measures important parameters that U-Scan Calci does not assess, including oxalate, citrate, and total daily excretion of stone-forming substances. The difference is that a laboratory test provides a detailed snapshot, while home monitoring can help reveal trends between those snapshots.

For example, regular measurements may help you explore whether changes in your drinking habits are reflected in your hydration-related readings, whether urinary calcium concentrations are changing, or how your urine pH responds over time. These observations can provide useful context for discussions with your healthcare team. However, urinary calcium concentration is not the same as total calcium excretion over 24 hours, and hydration-related measurements cannot directly establish whether you've reached your daily urine-volume target. That's why home readings should be interpreted as complementary information rather than substitutes for laboratory results.

Turning your results into useful conversations

U-Scan Calci membership also includes an initial video consultation with a registered dietitian nutritionist specializing in kidney health, provided through Fay. You can also generate a PDF summarizing your urinary trends over 30, 60, or 90 days and share it with your urologist or metabolic stone specialist during your next appointment. Rather than relying only on what you remember about your habits over the past few months, you can bring a record of how selected urinary indicators have changed over time.

The goal is simple: make it easier to stay engaged with your health between clinical assessments.

An important note about medical use

U-Scan Calci measurements can only be used for self-tracking purposes, it can’t be used for diagnosis of any disease or condition including clinical dehydration, kidney disease, diabetes, any deficiency or any other disease and conditions. U-Scan Calci measurements are not intended for medical use, including self-diagnosis or consultation with a doctor, and are only designed for general fitness and wellness purposes. Always consult your healthcare provider for any medical concerns or before making decisions about your health. Do not disregard or delay seeking medical advice based on information derived from this device.

The studies discussed earlier describe findings from populations of patients with kidney stones. They were not conducted using U-Scan Calci and do not establish that using this device reduces kidney stone formation or recurrence.

The take-home message? Your 24-hour urine test provides the detailed metabolic picture. Regular home monitoring may help you better understand selected urinary trends between tests, making it easier to discuss your habits and observations with your healthcare team.

Before your collection: what about food?

One of the first questions people ask when they discover they have kidney stones is simple: "What should I eat and what should I avoid?"

That's where things can get confusing!

Oxalate is often the first nutrient people worry about. A quick internet search will produce countless lists of foods to avoid, but there's a problem: these lists frequently disagree. That's partly because oxalate content can vary considerably between foods, and even within the same food, depending on the variety, growing conditions, and preparation methods. To help make sense of this information, we've put together a low-oxalate food guide covering 433 foods, based on published research into their oxalate content. You can explore the complete guide here: Low-Oxalate Food List. But before you start eliminating spinach, nuts, chocolate, or other foods from your diet, there is something important to understand. Not everyone who forms kidney stones needs a low-oxalate diet.

If your 24-hour urine test shows elevated oxalate excretion, reducing foods that are particularly high in oxalate may be helpful. But if your urinary oxalate is normal and your citrate is low, focusing on citrate and other relevant risk factors may be more useful than restricting oxalate unnecessarily.

Here is another important point: cutting back on calcium is usually not the answer. For most people with calcium oxalate stones, maintaining adequate dietary calcium helps bind oxalate in the intestine, reducing the amount absorbed and subsequently excreted in urine. That is why kidney stone prevention isn't about following the longest list of forbidden foods. It's about understanding which dietary changes actually matter for your individual urine chemistry.

The bottom line? Before making major changes to your diet, complete your metabolic evaluation while following your usual eating and drinking habits, unless your healthcare professional advises otherwise. Your 24-hour urine results can then help you make smarter, more targeted dietary choices, without giving up foods unnecessarily.

Frequently asked questions

How long does it take to get my 24-hour urine test results?

Usually one to two weeks, although turnaround times vary between laboratories. Your results may be available sooner, but your healthcare professional may need additional time to review them and explain what they mean for your kidney stone prevention plan.

Can I do a 24-hour urine test at home?

Absolutely! In fact, that's how it's usually done. You collect your urine at home over 24 hours, following the instructions provided with your kit. The samples are then analyzed in a specialized laboratory. With services such as Litholink, the collection kit can be delivered directly to your home and returned using the supplied shipping materials. You may not even need to visit a collection center.

Do I need to fast before a 24-hour urine collection?

No. Quite the opposite! For an initial metabolic evaluation, you should generally eat and drink as you normally would. The goal is to understand your usual urine chemistry, not how your body behaves when you temporarily change your diet. If you're taking medication or following a prescribed diet, continue as instructed by your healthcare professional.

What happens if I forget to collect some urine?

Don't panic, but don't ignore it either! Missing even one urination can make your results less reliable by underestimating your daily urine volume and the amount of substances excreted. Tell your laboratory if you miss a sample or accidentally spill some urine. You may need to repeat the collection. It's better to collect again than to base your prevention plan on inaccurate results.

Can I drink coffee or alcohol during the collection?

If coffee is part of your normal routine, you can generally continue drinking it during the test. Alcohol is a little different. You should avoid excessive drinking, and if you normally consume alcohol, ask your healthcare professional whether you should maintain your usual habits during the collection. The important principle is to avoid making unusual changes to your diet or fluid intake just for the test.

Do I need to refrigerate the urine container?

Follow the instructions provided by your laboratory. Many collections need to be refrigerated or kept cool during the 24-hour period. Others use preservatives and may have different storage requirements. If your container contains a chemical preservative, handle it carefully and keep it away from children and pets. When in doubt, contact the laboratory before starting.

How often should I repeat a 24-hour urine test?

That depends on your stone history, metabolic abnormalities, and treatment plan. A follow-up collection is commonly recommended within three to six months after starting or changing preventive treatment to check whether the intervention is working. If your results are stable and your prevention plan is effective, annual testing may be appropriate. Your urologist or metabolic stone specialist will determine the best schedule for you.

How is U-Scan Calci different from a 24-hour urine test?

They serve different but potentially complementary purposes. A laboratory-based 24-hour urine test provides a comprehensive metabolic evaluation, including daily urine volume and the excretion of calcium, oxalate, citrate, sodium, and other stone-related substances. U-Scan Calci is a home-monitoring device designed to track selected urinary indicators, including calcium concentration, urine pH, and hydration-related measures. With regular measurements, it can help you observe how these indicators change between laboratory assessments. However, it cannot measure total daily calcium excretion, calculate a complete stone-risk profile, or replace your 24-hour urine collection. U-Scan Calci is a General Wellness device, not a diagnostic medical test. It is intended to support awareness of urinary trends and does not replace clinical testing or professional medical advice.

Is a 24-hour urine test covered by health insurance?

In the United States, many insurance plans cover 24-hour urine testing when it is medically indicated, particularly for patients with recurrent kidney stones. However, coverage varies depending on your insurance provider, laboratory network, deductible, and the specific tests ordered. Before starting, check with your insurer or laboratory to understand any out-of-pocket costs.

Is a 24-hour urine stone-risk panel the same as a regular 24-hour urine test?

Not exactly. The collection method may be similar, but the measurements are different. A kidney stone-risk panel measures substances involved in stone formation, such as calcium, oxalate, citrate, uric acid, and sodium. It may also calculate urinary supersaturation for different stone types. Other 24-hour urine tests may be ordered for different reasons, such as measuring urinary protein, assessing creatinine clearance, or investigating hormonal and metabolic conditions. The important thing is to make sure your healthcare professional orders a metabolic stone-risk panel when the goal is kidney stone prevention.

Do children need a 24-hour urine test?

Sometimes, yes. Children who develop kidney stones may have underlying metabolic or genetic conditions that deserve careful evaluation. However, collecting urine over 24 hours can be challenging, particularly in younger children who are not yet toilet-trained. Research suggests that routine 24-hour urine testing in some children experiencing their first stone may not always change treatment decisions (Carnes et al., 2021). That doesn't mean metabolic evaluation should be overlooked. A pediatric nephrologist or urologist can determine whether a full 24-hour collection, age-adjusted spot urine tests, blood tests, or other investigations are most appropriate.

References

1. Pearle MS, Goldfarb DS, Assimos DG, Curhan G, Denu-Ciocca CJ, Matlaga BR, et al. Medical management of kidney stones: AUA guideline. J Urol. 2014;192(2):316-324. doi:10.1016/j.juro.2014.05.006
2. Curhan GC, Willett WC, Speizer FE, Stampfer MJ. Twenty-four-hour urine chemistries and the risk of kidney stones among women and men. Kidney Int. 2001;59(6):2290-2298. doi:10.1046/j.1523-1755.2001.00746.x
3. Alruwaily AF, Dauw CA, Bierlein MJ, Yan P, Asplin JR, Ghani KR, et al. How much information is lost when you only collect one 24-hour urine sample during the initial metabolic evaluation? J Urol. 2016;196(4):1143-1148. doi:10.1016/j.juro.2016.04.074
4. Ganesan C, Thomas IC, Song S, Sun AJ, Sohlberg EM, Kurella Tamura M, et al. Prevalence of twenty-four hour urine testing in veterans with urinary stone disease. PLoS One. 2019;14(8):e0220768. doi:10.1371/journal.pone.0220768
5. Carnes K, Howe A, Feustel PJ, Listman JA, White M, Kogan BA. 24-Hour urine collection for first time pediatric stone formers: Is it worth it? J Pediatr Urol. 2021;17(3):387.e1-387.e7. doi:10.1016/j.jpurol.2020.12.001