If you’ve been diagnosed with uric acid kidney stones or suspect that they might be the type of stone you’re forming, one of the most important tools in prevention is the 24-hour urine test. This simple but powerful test can reveal the unique chemistry of your urine and help determine the most effective strategies for reducing your stone risk.
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What Is a 24-Hour Urine Test?
A 24-hour urine test involves collecting all of your urine over a 24-hour period and sending it to a lab for analysis. The test measures the levels of various compounds in your urine that are known to contribute to stone formation. These include uric acid, calcium, citrate, sodium, oxalate, pH, and your total urine volume, among others.
This test is incredibly useful because stone prevention is not one-size-fits-all. While certain guidelines apply to nearly everyone (like drinking more fluids), most dietary recommendations should be based on your specific test results.
When to Take a 24-Hour Urine Test
If you’ve never done a 24-hour urine test before, it’s best to do it before making major dietary changes. Try to eat and drink the way you did when you were forming stones. This gives your healthcare provider a clear picture of your baseline risk. Ideally, you’ll do two tests—one on a weekday and one on a weekend—to capture any differences in your routine.
Once you’ve completed a test and implemented lifestyle changes, repeating the 24-hour urine test can show whether your changes are working. It allows you to compare your before and after results and fine-tune your approach.
What to Look for in Your Results
Supersaturation Levels
Your test results will include supersaturation levels for several types of stones:
- Calcium Oxalate
- Calcium Phosphate
- Uric Acid
Supersaturation measures how concentrated your urine is with these stone-forming compounds. The more supersaturated your urine is, the more likely these compounds will crystallize and form stones.
Even if your supersaturation appears within the “normal” range, that doesn’t necessarily mean you’re in the clear. If you’re actively forming stones, then your supersaturations are too high for you personally. The general goal in stone prevention is to cut your relevant supersaturation levels in half.
If you’re a uric acid stone former, you should pay close attention to the uric acid supersaturation number. A target of less than 1.0 is generally recommended to reduce the likelihood of stone formation.
Urine Volume
Your total urine volume reflects your overall fluid intake and is a crucial part of kidney stone prevention. A common goal for stone formers—especially those with uric acid stones—is to produce at least 2.5 to 3 liters of urine per day. Achieving this level of urine output helps dilute stone-forming substances, including uric acid, and lowers your overall risk of crystal formation.
Since not all the fluids you drink are excreted as urine (some are lost through sweat, breathing, and digestion), you’ll likely need to drink closer to 3 to 4 liters of water daily to meet your urine volume target. This amount may need to be even higher if you sweat a lot due to exercise, heat, or a physically demanding job.
If your urine volume is below 2.5 liters, increasing your fluid intake is one of the simplest and most effective strategies you can implement. In fact, raising your urine volume alone can have a significant impact on your uric acid supersaturation—a key factor in stone formation. Aiming for a uric acid supersaturation of less than 1.0 is much more achievable when urine volume is high enough to keep everything well diluted.
Urine pH
Uric acid stones form in acidic urine. A urine pH below 5.5 creates the perfect environment for these stones to develop. The goal is to raise your pH into a more neutral range, ideally between 6.5 and 7.0.
Paying close attention to urine pH is especially important for uric acid stone formers because it’s one of the few types of stones that can actually be dissolved by increasing pH. This makes managing your urine pH not just preventative, but potentially curative.
On your 24-hour urine test, look for the pH value and the uric acid supersaturation. These two numbers work hand in hand. Uric acid becomes more soluble—and less likely to form crystals—when urine is less acidic. Supersaturation levels of uric acid are much easier to reduce when the urine pH is within the ideal range. A supersaturation value of less than 1.0 is typically recommended to reduce the risk of stone formation.
To increase your urine pH:
- Reduce your intake of non-dairy animal proteins such as red meat, poultry, and seafood.
- Increase your intake of fruits and vegetables, which help neutralize acid in the body.
- Your doctor may prescribe medications like potassium citrate to help raise your pH more effectively.
By focusing on raising urine pH and lowering uric acid supersaturation, you can make significant strides in reducing your risk of forming new stones and even dissolve smaller ones that may already exist.
Citrate
Citrate (or citric acid) is a stone-inhibiting compound found in urine. For uric acid stones, citrate is helpful because it raises urine pH and prevents crystals from forming.
Low urine citrate is defined as under 400–450 mg/day. To increase your citrate levels:
- Eat more fruits and vegetables
- Cut back on excess protein
- Add lemon juice to water (about ½ cup in 2 liters of water per day)
- Discuss citrate-boosting medications with your doctor
If you experience frequent diarrhea, let your doctor know. It can lower urine citrate and increase stone risk.
Urine Uric Acid
This measures how much uric acid your body is excreting. While urine pH is the bigger risk factor for uric acid stones, high levels of uric acid in your urine (typically above 750 mg/day) still increase your stone risk.
Uric acid is produced when your body breaks down purines, which are found in many foods. Ways to reduce uric acid levels include:
- Moderating total protein intake
- Limiting red meat and seafood
- Avoiding excess added sugars
- Reducing alcohol intake (especially beer)
- Avoiding foods high in MSG or MSG-like additives
If your levels are high, your doctor may also prescribe medication to help lower your uric acid levels.
Summary: Key Targets for Uric Acid Stone Formers
If you form uric acid stones, here are the key urine test metrics to focus on:
- Uric acid supersaturation: Aim for <1.0
- Urine volume: Aim for 2.5–3 liters or urine output per day
- Urine pH: Target 6.5–7.0
- Urine uric acid: Aim for <750 mg/day
- Citrate: Aim for >400 mg/day
Your 24-hour urine test results can empower you to make strategic, personalized changes to your diet and lifestyle. Want more support interpreting your 24-hour urine test and building a prevention plan that works for you? Sign up for my free newsletter to get regular insights and tools to help you stay stone-free.
