Off Clamp Randomization: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Off Clamp Randomization (NCT01732120), a randomized na study. The primary outcome is Percent Change From Baseline in eGFR.

2. Clinical Question

3. Trial Design

This was a randomized, parallel-group trial with single masking. It was marked completed, with enrollment of 80. The study began in 2012-11 and had primary completion on 2017-05-31. Its phase is recorded as NA. Washington University School of Medicine was the sponsor.

The study compared off-clamp partial nephrectomy with traditional partial nephrectomy. In the off-clamp procedure, the renal blood vessels were not clamped; in the traditional procedure, they were clamped. The registry describes the purpose as comparing kidney-function effects after tumor removal with or without clamping. It does not report who was masked, how randomization was generated or implemented, or whether allocation was concealed.

The primary endpoint was percent change in eGFR from baseline to 3 months after nephrectomy. The posted primary outcome gives estimates for 34 participants in the off-clamp group and 37 in the traditional group. The registry separately notes missing postoperative eGFR for 6 people in the off-clamp group and 3 in the traditional group. How missing measurements were handled in the reported estimates is not reported in the registry record.

Secondary outcomes listed include blood loss, operative and warm ischemia times, surgical margins, metastasis, complications, and hospital days. Numerical results are posted for selected continuous outcomes; results for the other listed outcomes are not reported in the registry record. The record does not provide a detailed protocol or describe the intended statistical analysis plan.

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.

Overall Study

Analysis population for the primary outcome, as defined in the registry: Missing 3 postoperative eGFR from the Traditional Partial Nephrectomy group and 6 from the Off-Clamp Partial Nephrectomy group.

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 Percent Change From Baseline in eGFR, measured over baseline and 3 months post nephrectomy.

The primary endpoint measures the percent change in estimated glomerular filtration rate (eGFR) between baseline and 3 months after nephrectomy. eGFR is a clinical estimate of how well the kidneys filter blood; a change from baseline describes how the estimate differed after surgery from its starting value. The endpoint therefore focuses on kidney function over the stated follow-up interval, rather than on the surgical procedure alone.

The registry reports a mean percent change of -10.7 for off-clamp partial nephrectomy, with a 95% confidence interval from -16.1 to -5.3. For traditional partial nephrectomy, the mean is -9.4, with a 95% confidence interval from -14.0 to -4.8. These are group estimates, not a direct estimate of the difference between groups. A comparative primary-endpoint estimate or test is not reported in the registry record.

In general, using a baseline-to-follow-up change can account for where the measurement began, while the mean describes the average change in a group. The confidence interval conveys uncertainty around that group estimate under the method used. The registry does not report additional details about the eGFR calculation or the statistical method used to form these intervals.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a group mean describe?

The primary outcome is a continuous measure: percent change in eGFR from baseline to 3 months after nephrectomy. A mean summarizes the average observed change in each group. The registry gives means of -10.7 for off-clamp partial nephrectomy and -9.4 for traditional partial nephrectomy. These are within-group summaries. They are not themselves a comparison of the groups, and the registry does not report an inferential comparison for this endpoint.

For the selected secondary continuous outcomes, the record gives means and standard deviations by group. A standard deviation describes variation among measurements within a group; it is different from a confidence interval, which expresses uncertainty around an estimate. The secondary recalculations use posted group summaries to estimate unadjusted differences in means. In each comparison, the stated direction is traditional partial nephrectomy relative to off-clamp partial nephrectomy.

How should confidence intervals and p-values be read?

In general, a confidence interval gives a range of values reasonably compatible with the observed data under a specified statistical method. Narrower intervals indicate more precision than wider intervals, all else equal. An interval for a difference that includes zero is consistent with no difference under that interval-based analysis; an interval that excludes zero is evidence against a zero difference under the same assumptions. Neither statement establishes clinical importance or causation on its own.

A p-value describes how unusual data at least as incompatible with a null hypothesis would be if that hypothesis and the model assumptions held. It is not the probability that the null hypothesis is true, and it does not measure the size or practical importance of an effect. The posted secondary p-values are unadjusted; they do not address the multiplicity arising from assessing several outcomes. No adjusted analyses are reported. No primary-endpoint p-value is reported in the registry record.

What do the recalculated comparisons represent?

The secondary comparisons are simple, unadjusted recalculations from the posted group summaries. Estimated blood loss has a recalculated mean difference of -5.6, with a 95% confidence interval from -93.48 to 82.28 and p = 0.901. Operative time has a recalculated mean difference of -22.0, with a 95% confidence interval from -40.64 to -3.355 and p = 0.021. Warm ischemia time has a recalculated mean difference of 19.1, with a 95% confidence interval from 16.78 to 21.42 and p < 0.001. The registry record does not list sponsor-reported analyses for these comparisons. The recalculations should not be treated as adjusted estimates or as a substitute for an analysis plan.

In general, unadjusted comparisons do not account for baseline characteristics or other covariates. They also do not account for the possibility that multiple examined outcomes will produce some apparently notable results by chance. The registry does not report whether an adjusted analysis was planned, which covariates might have been used, or how the outcomes were prioritized beyond identifying the primary endpoint.

How should the sample-size illustrations be understood?

The posted planning illustrations are based on the observed secondary effects, not on the trial’s original design. Their stated assumptions are a two-sided significance level of 0.05, equal allocation, and a normal approximation. The rows describe planning for 100%, 75%, or 50% of the observed effect, and report participants per arm for 80% or 90% power. These are prospective planning illustrations, not observed power, and they do not show what power this completed trial had.

In general, a planning calculation estimates the sample size needed to detect an assumed effect under stated assumptions. The result depends on the effect chosen and on assumptions about variability and analysis. When the observed effect is used as the starting point, the illustration is data-dependent; it should not be read as evidence that the original study was designed around that effect. The very small warm-ischemia planning values arise from the particular observed contrast and the calculation assumptions, not from an independent confirmation of the result. The registry does not report the trial’s original sample-size justification.

For continuous outcomes, unequal variability, departures from model assumptions, missing data, and other design features can affect precision. In general, over-dispersion means that observed variability is greater than a model expects; ignoring it can make uncertainty appear too small. The registry does not report an over-dispersion assessment or the diagnostics used for these outcomes.

10. Multiplicity, Missing Data and Analysis Populations

The registry identifies percent change in eGFR as the primary outcome, but does not report a comparative primary analysis. It lists 10 outcome measures and 8 secondary outcomes; selected secondary summaries are posted, while reported analyses are absent for those outcomes. The registry does not report a multiplicity adjustment, an outcome hierarchy, or a prespecified approach for interpreting several outcomes together. Unadjusted secondary p-values should therefore be interpreted cautiously.

Missing postoperative eGFR is explicitly noted: 3 measurements are missing in the traditional partial nephrectomy group and 6 in the off-clamp group. The record does not report why the measurements were missing, whether the absence was related to participants’ health or outcomes, or how missing values were handled in calculating the group means and confidence intervals. In general, missingness can affect an estimate if the observed participants differ systematically from those without measurements. The record does not provide enough information to assess that possibility.

The primary outcome summaries report 34 participants for off-clamp partial nephrectomy and 37 for traditional partial nephrectomy, while enrollment is recorded as 80. These figures describe different elements of the registry record; the reason for the difference between enrollment and the endpoint summaries is not reported. The analysis population, including whether it followed intention-to-treat principles, is not reported in the registry record.

The record does not describe interim analyses, a statistical analysis plan, covariate adjustment, or methods for handling missing secondary outcomes. It also does not state whether analyses followed the randomized assignment regardless of the procedure received. Without those details, the reported summaries cannot be fully evaluated as a prespecified analysis of all randomized participants.

11. 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: pseudoaneurysm (5.0%), acute pulmonary embolism (2.5%), postoperative bleeding (2.5%), sepsis (2.5%).

The registry reports serious adverse events for 2 participants in the off-clamp group and 4 in the traditional group; each group lists 40 at risk. Deaths are reported for 1 participant in the off-clamp group and 0 in the traditional group. The record also reports other adverse events for 0 in the off-clamp group and 4 in the traditional group. These are counts as posted, not adjusted comparisons of safety.

The registry lists pseudoaneurysm at 5.0%, acute pulmonary embolism at 2.5%, postoperative bleeding at 2.5%, and sepsis at 2.5% among the most frequent serious-event terms. The record does not provide event-specific comparative analyses or explain whether event terms could overlap within participants. The percentages should therefore be read as the registry’s posted term frequencies, not as evidence of a causal relationship to either procedure.

In general, adverse-event counts are informative but do not by themselves establish that one approach is safer. Interpretation depends on how events were defined, collected, and attributed, along with the population observed and the precision of any comparative estimate. Those details and a comparative safety analysis are not reported in the registry record.

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

The registry record describes a randomized comparison of two partial nephrectomy techniques and reports group means for change in eGFR at 3 months. The estimates offer a description of kidney-function measurements among participants included in those summaries. Because the record does not report a between-group estimate or test for the primary endpoint, it does not quantify the comparative primary effect or its precision.

The selected secondary recalculations describe differences in some surgical measurements, but they are unadjusted and do not account for multiple outcomes. Other listed secondary outcomes lack numerical results in the record. The adverse-event figures are counts and term frequencies rather than adjusted safety comparisons. Together, these findings provide partial descriptive information, not a complete assessment across all outcomes.

Random allocation can support causal comparisons when assignment, follow-up, outcome measurement, and analysis are adequately conducted. The registry does not report enough detail about those processes, the analysis population, or handling of missing measurements to assess them fully. The posted results therefore should not be interpreted as proving that either procedure improves or worsens kidney function, or as establishing an overall advantage or disadvantage.

In general, statistical evidence about a group average does not determine what will happen to an individual participant. Clinical importance also depends on the magnitude of a difference, its uncertainty, and the relevance of the outcome to patients and clinical decisions. Those judgments require information beyond the posted group summaries. No treatment recommendation follows from these results alone.

13. Why This Trial Matters Statistically

This trial addresses a statistical challenge common in procedural research: comparing a change in a continuous clinical measure while also examining several technical and safety outcomes. The randomized parallel design offers a framework for comparing off-clamp and traditional partial nephrectomy, and the primary endpoint focuses on kidney function after surgery rather than only on what occurred during the operation.

The record illustrates why reporting a group mean is not enough to answer a comparative question. It gives a mean and confidence interval for each arm, but does not report a primary between-group estimate. A reader can see the observed group summaries, yet cannot use them as a substitute for the missing comparative analysis. Clear reporting of the contrast and its uncertainty is essential for understanding what the trial can support.

The selected secondary recalculations also illustrate the distinction between an observed result and a confirmatory conclusion. Their estimates and unadjusted p-values describe the posted data under simple assumptions, while the lack of a reported multiplicity strategy limits their evidential weight. The planning illustrations further show how sample-size calculations depend on the assumed effect and method; they are not a retrospective measure of whether the completed trial had adequate power.

Finally, the noted missing eGFR measurements and the absence of details about analysis populations and missing-data handling highlight the importance of transparent reporting. These issues matter not because they determine the result in advance, but because they shape how precisely and reliably readers can interpret the comparison.

14. 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.

A central limitation of the registry record is that it reports primary outcome estimates by group but not a comparative estimate or test. The confidence intervals describe each group’s mean; they do not replace a direct contrast. The record also does not explain the method used to calculate the primary confidence intervals.

Postoperative eGFR is missing for 3 participants in the traditional group and 6 in the off-clamp group. Reasons for missingness and methods for handling it are not reported. The analysis population and whether the primary analysis followed randomized assignment are also not reported. These gaps make it difficult to assess possible effects of missing measurements or exclusions.

For secondary outcomes, numerical results are available for selected continuous measures, while results for the other listed outcomes are not reported in the registry record. The recalculated secondary comparisons are unadjusted, and a multiplicity strategy is not reported. No sponsor-reported analyses are listed for these comparisons. The secondary findings therefore cannot provide a comprehensive or clearly confirmatory account of all outcomes.

Important design and conduct details are not reported, including who was masked, how randomization was implemented, the original sample-size justification, and whether interim analyses occurred. The stated follow-up for the primary endpoint is 3 months; longer-term kidney-function results are not reported in this record. The extent to which the results apply beyond the people represented in the trial cannot be assessed from the registry information alone.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Off Clamp Randomization — NCT01732120.
• Registry record last updated 2023-05-19; status last verified 2022-07.
• Results first posted 2022-06-09.
• 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.

18. Record Summary

NCT01732120, titled “Off Clamp Randomization,” is a completed, randomized, single-masked, parallel-group study sponsored by Washington University School of Medicine. Enrollment is recorded as 80. The study compared partial nephrectomy without clamping the renal blood vessels with traditional partial nephrectomy with clamping.

The primary outcome was percent change in eGFR from baseline to 3 months after nephrectomy. Group means and 95% confidence intervals are posted, but a comparative primary analysis is not reported. Selected secondary continuous outcomes have unadjusted recalculated comparisons; other listed secondary outcomes do not have numerical results in the registry record. Adverse-event counts are also posted, without a comparative safety analysis.

Missing postoperative eGFR is noted in both groups. The registry does not report the missing-data method, analysis population, multiplicity strategy, or original sample-size justification. Interpretation is consequently limited to the posted group summaries, selected secondary comparisons, and adverse-event counts.