Better Lithotripsy and Ureteroscopy Evaluation of Stenting (BLUES): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Better Lithotripsy and Ureteroscopy Evaluation of Stenting (BLUES) (NCT05026710), a randomized na study. The primary outcome is Change in Patient-Reported Outcomes Measurement Information System (PROMIS®) Scores of Pain-intensity at 7 to 10 Days.

2. Clinical Question

The registry describes a pragmatic, randomized, multi-center comparative-effectiveness study. Its stated hypothesis is that the silicone stent will have superior outcomes compared with non-silicone stents. The primary question focuses on pain intensity during the early postoperative period, measured with a participant-reported questionnaire. Secondary outcomes extend the inquiry to pain interference, urinary symptoms, healthcare utilization, imaging findings, and stone-free status at later follow-up times.

This is a comparison of two stent materials in the context of ureteroscopy, not a comparison of surgery with no surgery. The posted primary analysis concerns the change in questionnaire score within each arm and a reported regression comparison between arms. Interpretation therefore needs to distinguish the arm-specific changes from the statistical test of whether outcomes differed between treatment groups.

3. Trial Design

BLUES is a randomized, parallel-group, multi-center comparative-effectiveness study sponsored by the University of Michigan. The registry lists the allocation as randomized and masking as none. The interventions are the Coloplast Imajin Hydro silicone ureteral stent and a non-silicone polyurethane/Percuflex stent from any manufacturer. The registry describes the study as pragmatic.

The record lists an enrollment of 224 participants and conditions of renal stone and ureteral stone. The study started on 2021-12-02, reached primary completion on 2024-07-01, and has a status of completed. The phase is listed as NA. The brief summary describes participant questionnaires and follow-up information collected approximately 60 days after surgery.

The primary outcome is change in PROMIS pain-intensity T-score from baseline to 7 to 10 days after surgery. The registry also lists secondary outcomes involving pain and urinary-symptom scores, healthcare utilization, abnormal imaging findings, and stone-free status. The specific analysis population for the primary outcome consists only of participants who completed both the baseline and follow-up surveys. The registry does not report a fuller account of allocation procedures, masking beyond the listed designation, or the analysis population definitions for every secondary outcome.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: For the purposes of this trial, enrollment was defined as those who were randomized, remained eligible prior to stent placement, and received the study intervention.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Participants were only included in the analysis if they completed both the baseline survey and the follow-up survey

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Change in Patient-Reported Outcomes Measurement Information System (PROMIS®) Scores of Pain-intensity at 7 to 10 Days, measured over Baseline, 7 to 10 days: Participants can fill out the survey at any time between 7 to 10 days after surgery..

The primary endpoint is change in the Patient-Reported Outcomes Measurement Information System pain-intensity score from baseline to 7 to 10 days after surgery. The measure is a three-item survey. Participants select a response for each item from 1=no pain to 5=very severe pain; the response sum is converted to a T-score ranging from 36.3 to 81.8. Higher scores indicate worse pain intensity. Change is defined as the follow-up T-score minus the baseline T-score.

A change score represents how a participant's measured pain intensity differs from their own baseline, rather than their follow-up score alone. Comparing change between randomized arms can account for baseline differences in the measured outcome, although the registry's primary analysis method is described as linear regression. The registry reports the arm-specific mean changes and 97.5% confidence intervals, as well as a p-value for the regression comparison.

Participant-reported pain is relevant to this study because the intervention is a ureteral stent and the trial evaluates outcomes experienced by participants after ureteroscopy. A questionnaire provides a structured way to measure that experience. The registry does not report a threshold for a clinically important change in this score, so the clinical importance of any measured difference cannot be determined from the score estimates alone.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the primary outcome estimate?

The endpoint is a change in a continuous T-score. The registry gives the mean change in each arm, rather than a median or a count of participants whose pain improved. A mean summarizes the average observed change in the analyzed participants, while variation between individuals is reflected partly in the confidence interval. The arm means do not by themselves answer whether the treatment groups differ; that requires a between-arm analysis.

The primary comparison is reported as linear regression. In general, linear regression estimates an association between a continuous outcome and one or more explanatory variables. It can be used to compare outcome values between groups and, depending on the model, account for other variables. The registry does not report the regression coefficient, model covariates, or a confidence interval for the between-arm estimate. Those details are therefore not reported in the registry record.

How should confidence intervals be read?

General explanation: a confidence interval describes the statistical uncertainty around an estimate under the assumptions of the analysis. A narrower interval indicates greater precision than a wider interval, but precision is not the same as clinical importance. For the primary endpoint, the registry reports 97.5% confidence intervals around the mean change in each arm. Those intervals concern the arm-specific means, not a direct interval for the contrast between arms.

For the secondary binary outcomes with available counts, recalculated intervals concern a risk difference: the difference in the proportions with the outcome across the two arms. A risk difference of zero represents no difference in those proportions. The recalculated intervals for the two available outcomes include zero, so they are compatible with no difference as well as with differences in either direction. Their breadth indicates that the estimates are not precise. These are unadjusted recalculations from the posted summary counts, not the sponsor's full analysis model.

What does a p-value say?

General explanation: a p-value measures how unusual data at least as inconsistent with a specified null hypothesis would be if that null hypothesis and the analysis assumptions were correct. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of an effect. The primary reported p-value is 0.26. It should be read alongside the endpoint estimates and the limitations in the reporting, rather than as proof that the groups are identical.

For the available secondary outcomes, the registry reports Chi-squared tests. The recalculated p-values use the posted counts and are unadjusted. Such tests assess evidence against equal proportions under their assumptions. With limited outcome counts, estimates may be imprecise, and a test result alone does not describe the range of plausible effect sizes.

What do the planning illustrations mean?

General explanation: a sample-size calculation asks how many participants would be needed under stated assumptions to detect an effect of a chosen size with a specified probability, or power. The illustrations associated with the recalculated secondary comparisons use the observed effect or a stated fraction of it, a two-sided significance level of 0.05, equal allocation, and a normal approximation. They are planning illustrations based on the observed effect, not the original trial's sample-size justification. They are not observed power and should not be read as evidence about whether this completed study was adequately powered. The registry does not report the trial's own sample-size justification or design assumptions.

The illustrations are especially sensitive to the effect size used. An observed effect can be unstable when estimated from limited data, and planning around a smaller assumed effect requires a larger sample under otherwise similar assumptions. These estimates describe hypothetical future planning, not additional trial findings.

What is not documented?

The registry does not report a detailed statistical analysis plan, an interim-analysis plan, or a multiplicity adjustment strategy. It also does not report the full primary regression specification, a between-arm effect estimate and confidence interval, or detailed missing-data methods. Without those details, readers cannot assess all modeling choices or determine whether the posted analyses follow a prespecified plan. The reported results remain interpretable as registry results, but these omissions limit independent assessment of their precision and robustness.

10. Analyses Reported by the Sponsor

For the primary endpoint, the registry reports arm-specific mean changes and a linear-regression p-value of 0.26. A recalculated unadjusted comparison is not reported for this continuous endpoint, so there is no separate recalculated estimate to compare with the sponsor's primary analysis. The regression estimate and its confidence interval are also not reported in the registry record.

For the two secondary binary outcomes with posted counts, the registry reports Chi-squared p-values of 0.44 and 0.85. The unadjusted recalculations from the posted summary counts yield p-values of 0.439 and 0.848, respectively. These are consistent with the sponsor's reported results after rounding; there is no discrepancy that would require preferring one result over the other. The recalculations are simple comparisons of posted counts and do not reproduce any unreported adjustment or model specification.

The sponsor's reported analysis remains the relevant analysis for the primary endpoint. The secondary recalculations are supplementary checks, not replacements for the trial's analysis plan. Since detailed methods for the primary regression and the broader statistical plan are not reported in the registry record, the degree to which the posted analysis reflects any prespecified procedures cannot be assessed.

11. Multiplicity, Missing Data and Analysis Populations

The registry lists multiple secondary measures alongside the primary pain-intensity endpoint. It does not report whether the analysis plan adjusted for multiple comparisons, prioritized secondary outcomes, or treated them as exploratory. When several outcomes are tested, the chance of at least one apparently notable result can increase even if there is no true difference on any outcome. General statistical practice addresses this issue by prespecifying priorities or using an adjustment strategy, but whether either approach was used in this study is not reported in the registry record.

For the primary endpoint, the registry specifies that only participants who completed both baseline and follow-up surveys were included. This complete-case rule means participants without either survey do not contribute to the reported primary analysis. The registry does not report the reasons for missing surveys, how many were missing at each time point, whether missingness differed by arm, or whether any sensitivity analyses assessed the effect of missing data. If survey completion is related to pain or treatment assignment, the analyzed participants may not represent all randomized participants. That is a general concern rather than evidence that bias occurred in this trial.

The registry gives an overall enrollment of 224, but the primary endpoint analysis reports 98 participants in the silicone arm and 96 in the non-silicone arm. The registry does not explain the full participant flow from enrollment through analysis in the primary outcome description. For the secondary outcomes, analyzed counts vary by outcome; reasons for those differences are not reported in the registry record.

The record does not provide enough detail to identify an intention-to-treat analysis population, per-protocol population, or other population definition beyond the primary complete-survey criterion. It also does not report an interim-analysis plan or a comprehensive statistical analysis plan. These omissions limit evaluation of prespecification, multiplicity, and the handling of incomplete outcome data.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: flank pain (1.9%), urinary tract infection (uti) (0.9%), hematuria (0.9%), nausea (0.9%), pyelonephritis (0.9%).

The registry reports serious adverse events for 3 of 107 participants at risk in the silicone arm and 2 of 108 participants at risk in the non-silicone arm. It reports other adverse events for 11 of 107 and 10 of 108 participants at risk, respectively. No deaths are reported in either arm. The record also lists flank pain, urinary tract infection, hematuria, nausea, pyelonephritis, and cystitis among the most frequent serious adverse-event terms.

These figures are descriptive counts recorded during the study. They do not by themselves establish that an event was caused by a stent, nor do they determine whether the groups differ in safety. The registry record does not provide a detailed account of event timing, severity beyond the serious-event classification, attribution, or statistical comparison. The number at risk is not the same as the number analyzed for the primary questionnaire endpoint, so safety counts and pain-score results describe different analysis populations.

13. What the Result Does, and Does Not, Mean

The primary result is a comparison of change in participant-reported pain intensity after ureteroscopy between two stent groups. The registry reports mean changes in each arm and a regression test with p = 0.26. The reported analysis does not establish a between-arm difference in the primary outcome. Because the regression estimate and its confidence interval are not reported, the precision of the direct comparison cannot be judged from the primary test alone.

The result also does not establish that the two stents are equivalent or that any difference is clinically unimportant. Equivalence or non-inferiority requires an appropriate design and a prespecified margin, neither of which is reported in the registry record. The record also does not report a threshold for a clinically important change in PROMIS pain-intensity T-score. The arm-specific confidence intervals describe uncertainty in mean change, not a formal equivalence assessment.

The primary analysis includes only participants with both surveys completed. This defines the analyzed population but leaves unanswered how missing responses affected the findings. The secondary evidence is limited because numerical comparisons are posted for only some of the listed outcomes, and the available recalculated intervals are broad enough to include no difference.

These findings describe outcomes recorded in this particular randomized study, with its stated population, interventions, follow-up, and analysis. They do not answer questions beyond the reported endpoints or establish broader effects outside the study setting. In particular, the registry record alone does not provide a complete statistical analysis plan, full participant flow, or all secondary results needed for a comprehensive assessment of the evidence.

14. Why This Trial Matters Statistically

This study illustrates why the distinction between an arm-specific outcome and a treatment contrast matters. The registry reports a mean change within each stent group, but the clinical comparison concerns how those changes differ between groups. A test of that contrast and its confidence interval are more directly informative than interpreting either arm's change in isolation. In this record, the primary test is reported, but the contrast estimate and confidence interval are not.

It also shows how outcome availability and analysis populations shape interpretation. The primary analysis uses participants with both baseline and follow-up surveys, while the posted secondary outcomes have different analyzed counts. Without a complete account of missing responses and participant flow, readers cannot determine how closely each analysis reflects all randomized participants.

Finally, a randomized design does not remove the need to report analysis choices. Details on the regression model, multiplicity, missing-data handling, and sample-size justification help readers assess precision and robustness. Their absence does not invalidate the posted results, but it limits how far those results can support a firm conclusion. The available findings are most informative when read as estimates with uncertainty, rather than as a simple yes-or-no verdict on the stent comparison.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The primary endpoint is self-reported pain intensity, and the registry lists masking as none. Participant reports are relevant to pain, but knowledge of treatment assignment could influence responses or survey completion. The registry does not report methods intended to address that possibility.

The primary analysis includes only participants with completed baseline and follow-up surveys. The registry does not report the amount or pattern of missing survey data, reasons for noncompletion, or sensitivity analyses. This leaves uncertainty about whether the analyzed group differed from participants without complete surveys.

The primary comparison is reported with a p-value but without the regression estimate or its confidence interval. The registry also does not report the regression covariates, multiplicity strategy, interim-analysis plan, or trial-specific sample-size justification. These omissions make it difficult to assess the planned analytical framework and the precision of the main between-arm estimate.

Numerical secondary results are incomplete, and the available secondary outcomes use different analyzed counts. Follow-up timing also varies by endpoint: the primary survey is completed within a 7 to 10 day window, while other outcomes extend to later follow-up. The registry record does not provide enough detail to assess all outcome-specific missingness or the reasons that analysis counts differ. Finally, no threshold for clinically important change in the primary score is reported, limiting interpretation of the practical importance of the numerical changes.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Better Lithotripsy and Ureteroscopy Evaluation of Stenting (BLUES) — NCT05026710.
• Registry record last updated 2025-10-28; status last verified 2025-10.
• Results first posted 2025-10-28.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

BLUES (NCT05026710) is a completed, randomized, parallel-group, multi-center comparative-effectiveness study sponsored by the University of Michigan. It compares a Coloplast Imajin Hydro silicone ureteral stent with a non-silicone polyurethane/Percuflex stent after ureteroscopy. The registry lists enrollment of 224 participants, a start date of 2021-12-02, and primary completion on 2024-07-01.

The primary outcome is change in PROMIS pain-intensity T-score from baseline to 7 to 10 days after surgery. The reported linear-regression comparison has p = 0.26. Arm-specific mean changes and 97.5% confidence intervals are reported, but the between-arm estimate and its confidence interval are not reported in the registry record. Numerical secondary results are available for two binary outcomes; the other listed secondary results are not reported. The primary analysis includes only participants with both surveys completed.