Research shows that standard urine tests cannot explain why some people form kidney stones in only one kidney while the other remains healthy. A 2026 study of 648 patients followed for 7 years found that one-sided stone formers had nearly identical urine chemistry to those with stones in both kidneys, suggesting that local kidney factors rather than body-wide chemical imbalances drive one-sided stone formation. According to Gram Research analysis, this finding challenges the traditional assumption that all kidney stones result from systemic metabolic problems.
Researchers studied why some people develop kidney stones in just one kidney while the other stays healthy, even though doctors usually expect stone formation to affect both kidneys when caused by metabolic problems. According to Gram Research analysis, a study of 648 patients over 7 years found that standard urine tests could not explain why stones formed in only one kidney. The findings suggest that local factors within individual kidneys, rather than body-wide chemical imbalances, may be responsible for one-sided stone formation. This discovery could change how doctors approach prevention and treatment for patients with recurring kidney stones.
Key Statistics
A 2026 research article analyzing 648 kidney stone patients over 7 years found that standard 24-hour urine tests could not explain persistent one-sided kidney stone formation, suggesting local kidney factors play a larger role than previously thought.
Among 648 patients studied from 2011 to 2024, only 22 had stones in one kidney, and their urine chemistry was nearly identical to the 618 patients with stones in both kidneys, with the only significant difference being slightly higher calcium levels (269 versus 184 mg per 24 hours).
A 2026 analysis of kidney stone patients found that removing or losing function of a stone-forming kidney resulted in different urine chemistry patterns, indicating that kidney-specific factors beyond body-wide chemical imbalances may drive one-sided stone formation.
The Quick Take
- What they studied: Why some people form kidney stones in only one kidney instead of both, and whether standard urine tests can explain this pattern.
- Who participated: 648 patients followed for an average of 7 years, divided into three groups: those with stones in both kidneys (618 patients), those with stones in one kidney (22 patients), and those whose stone-forming kidney was removed or no longer worked (8 patients).
- Key finding: Standard 24-hour urine tests, which measure chemicals that cause kidney stones, did not explain why some people formed stones in only one kidney. The only notable difference was slightly higher calcium in urine for one-sided stone formers, but this was not enough to account for the pattern.
- What it means for you: If you form kidney stones in only one kidney, the problem may not be fixable through diet or medication alone. Your doctor may need to look for local kidney problems rather than assuming your whole body has a chemical imbalance. Talk to your healthcare provider about whether additional testing might help.
The Research Details
Researchers looked back at patient records from 2011 to 2024 and compared urine test results from three groups of people. The first group had stones in both kidneys, the second had stones in only one kidney, and the third had their stone-forming kidney removed or was no longer working, so their urine came from the healthy kidney only. All patients provided 24-hour urine samples collected during their normal daily routine and regular diet. The researchers measured chemicals in the urine that are known to cause kidney stones, including calcium, citrate, uric acid, and creatinine. They used statistical methods to account for differences between groups and to correct for the fact that they were testing many different chemicals at once.
This research approach is important because it directly compares people with different stone-formation patterns to understand what causes the difference. By including patients whose stone-forming kidney was removed, the researchers could see what the urine from a healthy kidney looks like, which helped them understand whether the problem was with the whole body or just one kidney. This type of comparison is more powerful than just looking at one group of patients.
The study is reliable because it used real patient data collected over 13 years, giving a long-term view of stone formation patterns. The main limitation is that the group with one-sided stones was small (22 patients), which makes it harder to find differences. The researchers also corrected for multiple comparisons, which reduces the chance of false findings. However, because this is a retrospective study looking back at existing records rather than a controlled experiment, we cannot prove cause and effect.
What the Results Show
The researchers found that standard urine tests did not explain why some people formed stones in only one kidney. When they compared people with one-sided stones to those with stones in both kidneys, almost all the urine chemicals were similar between the two groups. The only statistically significant difference was higher urinary calcium in the one-sided stone formers (269 mg per 24 hours versus 184 mg per 24 hours). However, this difference alone was not large enough to fully explain why stones formed in only one kidney and not the other. The group with their stone-forming kidney removed had lower levels of creatinine and uric acid compared to the other groups, and lower citrate compared to the one-sided stone formers. These findings suggest that the problem is not a body-wide chemical imbalance that affects both kidneys equally.
The study found that patients whose stone-forming kidney was removed or no longer worked had different urine chemistry than the other groups. This group had lower creatinine and uric acid, which are waste products filtered by the kidneys. They also had lower citrate, a chemical that normally protects against stone formation. These differences suggest that kidney function itself may play a role in stone formation, not just the chemicals in the urine.
Previous research assumed that kidney stones form when the whole body has chemical imbalances that affect both kidneys. This study challenges that assumption by showing that one-sided stone formation cannot be explained by body-wide chemical differences. The findings align with emerging research suggesting that local factors within individual kidneys, such as structural abnormalities, genetic differences, or cellular changes, may be more important than previously thought.
The study has several important limitations. The group with one-sided stones was small (only 22 patients), which makes it harder to find real differences and easier to miss important patterns. The study looked back at existing medical records rather than following patients forward in a controlled way, so we cannot prove that urine chemistry causes or does not cause one-sided stones. The urine samples were collected under normal conditions, not under controlled laboratory conditions, which could introduce variability. Finally, the study did not measure all possible factors that might explain one-sided stone formation, such as kidney structure, blood flow, or genetic differences.
The Bottom Line
If you have kidney stones that form in only one kidney, ask your doctor whether standard urine tests are enough to guide your treatment. Your doctor may recommend imaging studies to look for structural problems in the affected kidney, or genetic testing if kidney stones run in your family. Moderate calcium intake and staying well hydrated remain reasonable preventive measures, but they may not be sufficient for one-sided stone formers. Confidence level: Moderate, based on this single study with a small sample size.
This research matters most for people who have had kidney stones in only one kidney, especially if they have had multiple stones over time. It also matters for doctors who treat kidney stone patients, as it suggests they should look beyond standard urine tests when stones form in only one kidney. People with a family history of kidney stones may also benefit from understanding that one-sided formation may have different causes than two-sided formation.
If your doctor recommends additional testing or treatment based on these findings, you should not expect immediate results. Kidney stone prevention is a long-term process. It typically takes several months to years to see whether preventive measures are working. Keep track of any new stones and discuss patterns with your doctor during regular follow-up visits.
Frequently Asked Questions
Why do some people get kidney stones in only one kidney?
Research suggests local factors within individual kidneys, such as structural differences or genetic variations, rather than body-wide chemical imbalances. A 2026 study found that urine chemistry was nearly identical between one-sided and two-sided stone formers, pointing to kidney-specific causes.
Can urine tests predict if I will form kidney stones in one kidney?
Standard 24-hour urine tests cannot reliably predict or explain one-sided kidney stone formation. A study of 648 patients found these tests showed almost no differences between one-sided and two-sided stone formers, suggesting additional testing may be needed.
Should I change my diet if I have one-sided kidney stones?
Moderate calcium intake and increased water intake remain reasonable preventive measures, but they may not fully prevent one-sided stones. Talk to your doctor about whether additional testing for structural or genetic factors might help guide your treatment plan.
What should I do if I keep forming stones in the same kidney?
Ask your doctor about imaging studies to check for structural problems in that kidney and consider genetic testing if kidney stones run in your family. Standard urine tests alone may not identify the cause, so additional evaluation could help guide treatment.
Want to Apply This Research?
- Log any new kidney stone episodes with the date, which kidney was affected, and any symptoms. Track this over months and years to identify patterns. Share this timeline with your doctor to help guide treatment decisions.
- If you have one-sided kidney stones, use the app to set reminders for daily water intake (aim for 2 to 3 liters per day) and to log your dietary calcium intake. This helps you and your doctor understand whether diet changes might help prevent future stones.
- Set up quarterly check-ins in the app to review your stone formation history and any new episodes. Use the app to track imaging results or genetic testing if your doctor recommends these. Share your app data with your healthcare provider during annual visits to help guide long-term management.
This article summarizes research findings and should not replace professional medical advice. Kidney stone formation is complex and may involve factors not covered in this study. If you have kidney stones or suspect you may develop them, consult with a urologist or nephrologist for personalized evaluation and treatment. Do not make changes to your diet, medications, or medical care based solely on this article without discussing with your healthcare provider first.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.