Kidney stones come back in about half of people who have surgery to remove them. Researchers followed 68 patients after stone removal surgery and found that checking urine chemistry at different times could predict who would get stones again. A special urine test measuring how likely stones are to form (called relative supersaturation) was very accurate at spotting high-risk patients. When doctors used this test to guide treatment decisions, patients had fewer stone recurrences. This suggests a personalized approach based on urine chemistry could help prevent painful kidney stones from returning.

The Quick Take

  • What they studied: Whether checking urine chemistry after kidney stone surgery could predict which patients would get stones again, and whether using this information to guide treatment would prevent recurrence.
  • Who participated: 68 adults who had successful kidney stone removal surgery between January 2023 and January 2024. All participants were stone-free after surgery and completed follow-up urine testing.
  • Key finding: Patients whose urine showed persistent high levels of stone-forming chemicals had about 7 times higher risk of stone recurrence. Using urine chemistry to guide treatment reduced stone recurrence from 29% down to 12% in high-risk patients—a significant improvement.
  • What it means for you: If you’ve had kidney stone surgery, a simple urine test might help your doctor predict your personal risk of stones returning and create a customized prevention plan. This approach appears more effective than standard care, though it requires specialized testing that may not be widely available yet.

The Research Details

This was a prospective cohort study, meaning researchers followed patients forward in time after their surgery. Sixty-eight patients who had successful kidney stone removal were enrolled and followed for up to 30 months. The researchers collected 24-hour urine samples (all urine produced in one day) at multiple time points: 2 weeks after surgery, then at 1, 3, 6, and 12 months. They measured specific chemicals in the urine that indicate how likely stones are to form again—a measurement called relative supersaturation (RSS). They also asked patients detailed questions about their diet using a food frequency questionnaire to understand eating patterns that might affect stone formation. The study tracked both whether stones came back (either seen on imaging or causing symptoms) and whether urine chemistry improved by at least 30% after treatment.

This research approach is important because it moves beyond just waiting to see if stones return—it identifies the underlying chemical problem in the urine that causes recurrence. By measuring urine chemistry repeatedly over time, researchers could see patterns that predict risk. This allows for personalized, targeted prevention rather than one-size-fits-all treatment. The study also tested whether using this information actually improved outcomes, which is crucial for determining if the test should be used in real clinical practice.

The study was approved by an institutional ethics committee and obtained written informed consent from all participants. The researchers used validated, established methods for measuring urine chemistry and a validated food frequency questionnaire. They used statistical modeling (multivariate analysis) to identify which factors independently predicted stone recurrence. The prediction model showed good accuracy with an AUC of 0.81 (on a scale where 1.0 is perfect prediction). However, this is a single-center study with a relatively small sample size, so results should be confirmed in larger populations before widespread implementation.

What the Results Show

During the follow-up period (median 24 months), 14 out of 68 patients (20.6%) experienced kidney stone recurrence. The researchers identified four independent predictors of recurrence: (1) persistently high calcium oxalate levels in urine (increased risk nearly 7-fold), (2) calcium phosphate levels above 1.5 on two or more visits (increased risk 4.4-fold), (3) uric acid-related stone formation linked to urine pH changes (increased risk 3.3-fold), and (4) low urine volume below 1.5 liters per day (increased risk 3.1-fold). The prediction model combining these factors was quite accurate, correctly identifying 74% of patients who would have recurrence and 78% of those who wouldn’t. Most importantly, when doctors used this urine chemistry information to guide personalized treatment, only 11.8% of high-risk patients had recurrence compared to 29.4% receiving standard care—a reduction of about 44% in absolute risk.

The study found that achieving at least a 30% reduction in relative supersaturation (the biochemical response) was associated with better outcomes. Dietary factors measured through the food frequency questionnaire appeared to influence urine chemistry patterns, suggesting that dietary modifications tailored to individual urine chemistry might be particularly effective. The researchers noted that urine volume was a modifiable factor—patients who increased their daily urine output to above 1.5 liters had lower recurrence risk, which is achievable through increased fluid intake.

Previous research has shown that kidney stones recur in about 50% of patients within 5 years. This study’s 20.6% recurrence rate over 24 months is lower than historical rates, likely because the patients received some level of intervention. The finding that urine chemistry patterns predict recurrence aligns with existing stone disease literature, but this study is novel in showing that serial (repeated) measurements over time improve prediction accuracy compared to single measurements. The effectiveness of RSS-guided intervention in reducing recurrence is a new finding that suggests personalized, chemistry-based approaches outperform standard care.

The study included only 68 patients from a single center, which limits how widely the findings apply to different populations. The follow-up period, while adequate, was relatively short (up to 30 months) compared to the typical 5-year recurrence window. The study doesn’t provide detailed information about what specific interventions were used in the RSS-guided group versus standard care, making it unclear exactly what doctors should do with the test results. The relative supersaturation test requires specialized laboratory capability that may not be available at all hospitals. The study also doesn’t address cost-effectiveness or practical implementation challenges in real-world settings.

The Bottom Line

For patients who have had kidney stone surgery: (1) Ask your doctor about urine chemistry testing (relative supersaturation) to assess your personal recurrence risk—this is a reasonable option if available at your medical center (moderate confidence). (2) Regardless of testing, increase daily fluid intake to produce at least 1.5 liters of urine daily, as this consistently reduces recurrence risk (high confidence). (3) Work with a dietitian familiar with kidney stone prevention to modify diet based on your urine chemistry if available (moderate confidence). (4) If you’re identified as high-risk based on urine chemistry, discuss targeted interventions with your urologist rather than relying on standard prevention alone (moderate confidence).

This research is most relevant for people who have had kidney stone surgery and want to prevent recurrence, especially those with a history of multiple stones or family history of kidney stones. It’s particularly valuable for patients at high risk based on their urine chemistry. Urologists and nephrologists should consider incorporating urine chemistry monitoring into their post-operative care protocols. This may be less immediately relevant for people who have never had kidney stones, though the prevention strategies (adequate hydration, dietary modifications) apply broadly.

Urine chemistry changes can be detected within 2-4 weeks of starting interventions, but meaningful reduction in recurrence risk typically requires 3-6 months of consistent prevention efforts. The study followed patients for up to 30 months, with most recurrences occurring within the first 12-24 months. You should expect to see whether your prevention strategy is working through repeat urine testing at 1-3 month intervals, with final assessment of recurrence risk at 6-12 months.

Want to Apply This Research?

  • Track daily fluid intake (target: at least 1.5 liters of water daily) and urine output volume. Log any dietary changes recommended by your doctor or dietitian, particularly intake of calcium, sodium, oxalate-rich foods, and protein. Record dates of urine chemistry tests and results to monitor trends in relative supersaturation values.
  • Set a daily reminder to drink water at regular intervals throughout the day to reach your 1.5-liter target. Use the app to log meals and compare them against a personalized dietary plan created based on your urine chemistry results. Set reminders for scheduled urine collection appointments and follow-up testing.
  • Create a dashboard showing your urine chemistry trends over time (if you have access to test results). Track correlations between dietary changes and urine chemistry improvements. Monitor symptom patterns (flank pain, urinary symptoms) to catch early signs of recurrence. Set quarterly check-in reminders to review progress with your healthcare provider and adjust prevention strategies as needed.

This research describes a promising new approach to predicting and preventing kidney stone recurrence, but it should not replace consultation with your urologist or nephrologist. The relative supersaturation test is not yet widely available and may not be covered by insurance. Individual results may vary based on genetics, underlying medical conditions, and medication use. If you have a history of kidney stones or are experiencing flank pain, urinary symptoms, or other concerning signs, consult your healthcare provider immediately. This summary is for educational purposes and does not constitute medical advice. Always discuss new prevention strategies with your doctor before implementing them, especially if you have other medical conditions or take medications that affect kidney function or urine chemistry.