Uric Acid and the Endothelium in CKD: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Uric Acid and the Endothelium in CKD (NCT01228903), a randomized na study. The primary outcome is Change in Endothelial Dependent Dilation From Baseline to Week 12.

2. Clinical Question

The clinical question concerns a proposed relationship between uric acid and vascular function in people with kidney disease. The study description says it tests the hypothesis that uric acid impairs vessel function. The randomized comparison assigns participants to allopurinol or placebo, then assesses vascular function outcomes. This design addresses whether the groups differ in the measured outcome over the study period; it does not, by itself, establish every possible biological pathway connecting uric acid and endothelial function.

The primary outcome is a change in a vascular function measure, rather than a direct measure of symptoms, kidney disease progression, or cardiovascular events. Those distinctions matter when interpreting what a group difference would mean. The reported primary comparison is a mean difference in change, with an interval estimate and a sponsor-reported analysis also recorded. The registry record does not report detailed eligibility criteria or a more specific description of the patient population.

3. Trial Design

The registry lists this as a randomized, double-masked, parallel-group study. Participants were assigned to allopurinol or placebo, and the groups were compared on vascular function outcomes. The parallel design means the treatment groups are distinct assignment groups rather than periods in which the same participants receive each intervention. The registry record does not report further details about how the random sequence was generated, how assignment was concealed, or who was masked.

Enrollment is listed as 80. The outcome summaries report 41 participants in the control group and 39 in the allopurinol group. These are the group counts associated with the posted outcome summaries; the registry record does not explain whether all enrolled or randomized participants contributed data to each analysis, or how missing measurements were handled.

The registry lists the study as completed, with a start date of 2010-10 and a primary completion date of 2016-09. The sponsor is University of Colorado, Denver. The interventions are allopurinol and placebo. The placebo is described as containing no active ingredient, while allopurinol is described as a medicine that lowers uric acid levels. Dose, treatment adherence, and details of concomitant care are not reported in the registry record.

The primary outcome is change in flow-mediated, endothelium-dependent dilation from baseline to week 12. The registry also lists changes in C-reactive protein, serum interleukin-6, monocyte chemotactic protein-1, and oxidized low-density lipoprotein over the same period. It lists six outcome measures, while four secondary outcomes are named in the record. The phase is listed as NA; a further phase description is not reported in the registry record.

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

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 Endothelial Dependent Dilation From Baseline to Week 12, measured over Baseline and 12 weeks.

The primary endpoint is change in endothelium-dependent dilation from baseline to week 12, measured by flow-mediated dilation. The registry expresses the outcome as a mean and gives its unit as % change. The posted group summaries report the average change and its standard deviation for the control and allopurinol groups.

As general statistical and physiological context, flow-mediated dilation is used as a measure of how a blood vessel responds to a stimulus that promotes dilation. The endothelium is the inner lining of blood vessels, and the endpoint is intended to represent a vascular function characteristic relevant to the study’s hypothesis about uric acid and endothelial function. Its use provides a measurable outcome for comparing the groups over the study period.

This endpoint is a measure of vascular function, not a direct measure of how participants feel, kidney disease progression, or clinical events. A difference in the measure would therefore describe a difference in this recorded physiological outcome; it would not, on its own, establish a difference in broader clinical outcomes. The registry record does not provide a more detailed protocol for measurement, including technical procedures or quality-control methods.

7. Results Posted in the Registry

• Allopurinol: mean 0.90 versus 0.20 on control; difference 0.70 (95% CI -1.05 to 2.45), standardized effect d = 0.17; z-test p = 0.434.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Change in C-reactive Protein From Baseline to Week 12

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Allopurinol: mean 0.42 versus 0.70 on control; difference -0.28 (95% CI -3.44 to 2.88), standardized effect d = -0.04; z-test p = 0.862.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Allopurinol and the control. The interval gives the range of effects that remain compatible with the data.

Change in Serum Interleukin-6 From Baseline to Week 12

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Allopurinol: mean 0.37 versus 0.15 on control; difference 0.22 (95% CI -1.05 to 1.49), standardized effect d = 0.08; z-test p = 0.735.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Allopurinol and the control. The interval gives the range of effects that remain compatible with the data.

Change in Monocyte Chemotactic Protein-1 From Baseline to Week 12

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Allopurinol: mean 3.60 versus -4.70 on control; difference 8.30 (95% CI -9.84 to 26.44), standardized effect d = 0.20; z-test p = 0.370.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Allopurinol and the control. The interval gives the range of effects that remain compatible with the data.

The four named secondary outcomes cover inflammatory and oxidative measures. Their estimated group differences do not all point in the same direction: the C-reactive protein comparison is negative, while the interleukin-6 and monocyte chemotactic protein-1 comparisons are positive. Across these posted comparisons, the recalculated unadjusted intervals include zero. This pattern does not offer a consistent set of secondary results that independently reinforces a clear group difference in the primary vascular measure.

The secondary outcomes provide additional context about the study’s broader biological questions, but they measure different quantities from flow-mediated dilation. A result on an inflammatory or oxidative marker would not be interchangeable with a result on the primary vascular function endpoint. Nor does the primary comparison determine what the secondary outcomes should show. The record lists four secondary outcomes, while the primary outcome is the change in endothelium-dependent dilation.

Unadjusted secondary results carry less weight when several outcomes are examined because each additional comparison creates more opportunities for a nominally notable result to arise by chance. General statistical practice may address this through a multiplicity strategy, but a strategy for these outcomes is not reported in the registry record. The posted p-values should therefore be interpreted as unadjusted, and isolated secondary findings should not be treated as confirmatory without further context.

The absence of a consistent directional pattern and the uncertainty in the individual comparisons make the secondary results best viewed as supporting descriptive information rather than a separate conclusion. The registry record does not report whether the secondary outcomes were prespecified in a hierarchy, whether any were considered exploratory, or how their analysis related to the primary analysis. These omissions limit how strongly the set of secondary results can be interpreted.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Change in C-reactive Protein From Baseline to Week 12
• Change in Serum Interleukin-6 From Baseline to Week 12
• Change in Monocyte Chemotactic Protein-1 From Baseline to Week 12
• Change in Oxidized Low Density Lipoprotein From Baseline to Week 12

9. Statistical Interpretation

10. Statistical Methods Explained

What does the mean difference represent?

The primary outcome is continuous: it is measured on a numerical scale rather than counted as an event. The registry reports a mean change for each group. The mean difference compares those group averages, with the order defined as allopurinol minus control. A positive estimate means the posted average change is higher in the allopurinol group; a negative estimate would mean it is lower. The estimate of 0.7 is in the registry’s stated unit, % change. It is a group-level contrast, not a description of every participant’s individual response.

The standard deviations describe the spread of participant measurements around each group mean. They are not standard errors and do not directly describe uncertainty in the difference between group averages. Standard errors quantify sampling uncertainty in an estimate; the recalculated interval uses that uncertainty to express a range of values compatible with the summary data under the calculation’s assumptions. The registry’s primary group standard deviations are 4.1 for control and 3.9 for allopurinol.

How should the interval and p-value be read?

A confidence interval is a statistical summary of the uncertainty around an estimated effect. In general, an interval extending across zero indicates that the data do not rule out zero difference under the method used, while also allowing nonzero differences within the interval. The primary recalculated interval extends from -1.053 to 2.453. It should not be read as a list of likely individual outcomes, nor as proof that all values inside it are equally plausible.

A p-value measures how compatible the observed data are with a specified null model under the chosen statistical procedure. It is not the probability that the null hypothesis is true, and it does not quantify the probability that a treatment benefit or harm exists. The recalculated unadjusted p-value is 0.434. Its interpretation is tied to the simple unadjusted comparison and its assumptions; it is not a substitute for evaluating the estimate, interval, design, or completeness of the data.

Why are there two analysis results?

The registry reports a sponsor analysis using the Wilcoxon (Mann-Whitney) method and labels the analysis type as equivalence. It gives a net mean difference of 0.7 and p = 0.47, without an interval or an equivalence margin. The recalculation instead uses the posted means and standard deviations for an unadjusted mean comparison. These are not identical methods. The Wilcoxon (Mann-Whitney) procedure is based on the ordering of observations and is often described as a rank-based comparison. It does not necessarily test exactly the same statistical quantity as a comparison of means under a model for the group averages.

The reported net mean difference and the recalculated mean difference both have a value of 0.7, but matching estimates do not make the underlying analyses interchangeable. A p-value can differ because a method uses different features of the data or makes different assumptions. The registry record does not provide the participant-level data, the sponsor’s full analysis details, or a confidence interval for its reported analysis. The record also does not state an equivalence margin, which is needed to assess a formal equivalence claim.

What does an unadjusted recalculation assume?

General statistical context: an unadjusted comparison treats the displayed group summaries as the basis for estimating a difference without accounting for covariates or other design features. It relies on the summaries accurately representing the analyzed observations and cannot correct for missing data or imbalances that are not described. The recalculated interval and p-value should therefore be understood as simple summaries from the posted statistics, not as a reconstruction of the full trial analysis.

For continuous outcomes, unequal variability can affect the uncertainty in a group comparison. Over-dispersion, in general, means that data vary more than a chosen model expects; if that extra variability is not represented, standard errors and intervals can be too optimistic. Here, the posted primary standard deviations are similar, but that alone does not establish the shape of the individual-level data or validate every modeling assumption. Participant-level distributions and diagnostic information are not reported in the registry record.

Randomization supports a between-group comparison by assigning participants to groups, but valid interpretation still depends on what happened after assignment and how data were analyzed. Information about adherence, losses to follow-up, outcome ascertainment, and missing-data methods is not reported in the registry record. The posted group summaries cannot answer those questions. They also do not show individual responses, so they cannot describe the range or pattern of change for particular participants.

11. Confidence Intervals and Precision

The recalculated primary mean difference is 0.7, with an interval from -1.053 to 2.453. The interval is wide enough to include zero and values in both directions. That means the estimate is not precise enough to distinguish clearly between no average difference and a range of potentially positive or negative differences, on the scale used for the endpoint. The interval’s width is important alongside the point estimate: the estimate alone gives a single value, while the interval communicates substantial uncertainty around it.

In general, a confidence interval is calculated by combining an estimated effect with its sampling uncertainty. It is not a guarantee that the true effect lies inside the interval, and it does not indicate the distribution of individual participant outcomes. The registry record does not report an interval for the sponsor’s Wilcoxon (Mann-Whitney) analysis. The recalculated interval therefore describes the unadjusted mean comparison based on the posted summaries, not the sponsor’s analysis.

The group standard deviations are 4.1 for control and 3.9 for allopurinol, indicating that individual changes vary around the group means. The reported group counts for the primary outcome are 41 and 39. Together, the variability and the available group counts shape the precision of the mean difference. The record does not report enough detail to assess whether every randomized participant contributed an outcome measurement or whether any missingness could affect the estimate.

Precision is distinct from statistical significance and from clinical importance. An interval spanning zero does not show that the groups are identical, while an estimate away from zero would not by itself establish that a difference matters clinically. The registry record does not state a threshold for a clinically important difference in this endpoint. Therefore, the statistical interval can describe uncertainty on the measurement scale, but cannot determine clinical importance on its own.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size figures are planning illustrations based on the observed effect, not the trial’s original design calculations. For continuous outcomes such as these, the displayed figures are participants per arm, not total events. The registry record’s planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each row considers an effect equal to the stated fraction of the observed effect. The original design assumptions are not reported in the registry record.

The 80% power column gives the planned participants per arm under the stated assumptions for a design with an 80% chance of detecting the specified effect if that effect were the true one. The 90% power column uses a higher target chance of detecting that effect. These are planning concepts: power is a property of a proposed study under assumptions about the effect, variability, and analysis. The figures are not evidence about how likely the completed study was to detect an effect after its results were observed.

The rows for smaller fractions of the observed effect require more participants per arm. In general, smaller effects are harder to distinguish from sampling variation, so detecting them with the same planned power requires more information. The displayed figures are conditional on the observed effect and the stated assumptions. They should not be read as recommendations for a future study without considering the scientific question, outcome, design, and other planning information. These figures are not observed power.

The sample-size display accompanies the outcome results, but it does not retrospectively show that the original trial was designed around these assumptions. The registry record does not report the trial’s original sample-size justification or its planned target effect.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 0.700; pooled standard deviation σ = 4.004.
2. n = 2 × (1.96 + 0.842)² × 4.004² / 0.700² = 513.6, rounded up to 514 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- 0.7                      # observed difference in means
sigma <- 4.00381228587366                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(1228903)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 514 (80% power), 688 (90% power)
 75% of observed effect: n per arm = 913 (80% power), 1,223 (90% power)
 50% of observed effect: n per arm = 2,055 (80% power), 2,751 (90% power)
power.t.test: 514.5 
Simulated power at n = 514 per arm: 0.795 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Analyses Reported by the Sponsor

The sponsor’s reported primary analysis uses the Wilcoxon (Mann-Whitney) method. The registry lists a net mean difference of 0.7 and p = 0.47, and marks the analysis type as equivalence. It does not report an interval estimate or an equivalence margin for that analysis.

The recalculation uses the posted group means and standard deviations to produce an unadjusted mean difference of 0.7, an interval from -1.053 to 2.453, and an unadjusted p-value of 0.434. The point estimate agrees with the sponsor’s reported value, while the p-values are not identical. That difference is not inherently a contradiction: the sponsor’s rank-based analysis and the recalculated mean comparison use different methods and may answer related but non-identical statistical questions.

The registry record indicates no discrepancy between the reported and recalculated results. The recalculation is a simple check based on summary statistics, not a substitute for the sponsor’s analysis or a reanalysis of participant-level data. The sponsor’s analysis is the reported trial analysis; its method, equivalence label, and results should be read as such. Without a reported equivalence margin, the record does not establish from the label alone whether a formal equivalence criterion was satisfied.

15. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when several hypotheses or endpoints are examined. Even when each individual analysis uses a conventional threshold, looking across multiple results increases the chance that at least one will appear notable by chance. This general issue is relevant because the registry lists a primary endpoint and multiple secondary endpoints. The record does not report a multiplicity adjustment, a hierarchy for testing outcomes, or a rule specifying which outcomes would be confirmatory.

Without that information, the secondary p-values should be read as unadjusted comparisons rather than as a family-wise confirmatory analysis. The primary outcome remains the designated primary endpoint in the registry, but the record does not report whether the sponsor’s analysis plan included additional safeguards for multiple testing. A lack of reported adjustment is not proof that none was used; it means the adjustment approach is not reported in the registry record.

Missing-data handling is also not reported. The outcome summaries include 41 participants in the control group and 39 in the allopurinol group, but the record does not state how many were randomized, whether the group counts represent all assigned participants, or whether some participants lacked measurements. It does not describe imputation, complete-case analysis, sensitivity analyses, or reasons for missing outcome data. Those details matter because results can be affected if missingness is related to treatment assignment or outcome values.

The analysis population is not described in the registry record. It is therefore not possible to determine from the posted information whether the sponsor used an intention-to-treat population, a per-protocol population, or another defined group. This matters particularly for an equivalence analysis, where exclusions or departures from assigned treatment can affect interpretation. The record also does not report an equivalence margin, a detailed statistical analysis plan, or interim-analysis procedures. No conclusions about those design and analysis choices should be inferred from their absence in the record.

16. Safety Results

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

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: death (2.6%).

The registry reports serious adverse events among 41 participants at risk in the control group, with 0 affected, and among 39 participants at risk in the allopurinol group, with 1 affected. These are counts of participants reported as affected in each group. The record also lists other adverse events among 9 participants in control and 4 in allopurinol, with the same group counts at risk as reported for the serious-event summaries.

The registry lists Death as a top serious adverse event term at 2.6%. The record does not provide a group allocation for this term in the posted summary, and the deaths field is not populated for the groups. The percentage should therefore not be used to infer which group experienced the event or to reconstruct group-specific counts.

These figures are descriptive safety summaries. They do not establish that an event was caused by an intervention, and the registry record does not provide details about event timing, severity beyond the serious classification, or attribution. The counts should be read in the context of the reported group sizes and the limited follow-up information, rather than as a complete assessment of comparative safety.

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

The primary result is an estimated mean difference of 0.7 in change in flow-mediated, endothelium-dependent dilation, with an interval from -1.053 to 2.453 and a recalculated unadjusted p-value of 0.434. The interval includes zero and extends in both directions. These posted data therefore do not establish a clear difference between the groups on this measured outcome, while also not demonstrating that the true difference is exactly zero.

The result concerns the recorded change from baseline to week 12 in a vascular function measure. It is not a direct estimate of effects on symptoms, kidney disease progression, cardiovascular events, or other outcomes. The registry record does not report results for those clinical outcomes. It also does not provide enough detail to determine whether the primary result would be different under another analysis population, missing-data approach, or adjusted analysis.

The sponsor’s reported analysis gives a net mean difference of 0.7 and p = 0.47 using the Wilcoxon (Mann-Whitney) method. The registry labels this an equivalence analysis, but does not report the equivalence margin or an interval for the sponsor’s analysis. A formal equivalence conclusion depends on a prespecified margin and an analysis that evaluates whether the uncertainty lies within that margin. The label and p-value alone do not show that criterion was met.

More broadly, a result that does not clearly distinguish a difference from zero can reflect uncertainty, rather than proof of no effect. Conversely, an estimated difference does not automatically establish clinical importance. No threshold for a meaningful change in this endpoint is reported in the registry record. The findings should therefore be interpreted as a comparison of the posted group summaries, with uncertainty and limitations, and not as medical advice or a definitive statement about treatment effects in all people with kidney disease.

18. Why This Trial Matters Statistically

This trial is statistically informative because it links a mechanistic hypothesis about uric acid and endothelial function to a randomized comparison of allopurinol and placebo. The primary endpoint is a continuous physiological measure, and the registry posts group means, standard deviations, a sponsor analysis, and summaries for additional biological outcomes. Together, these make it possible to distinguish the estimated size of a group difference from the uncertainty around it.

The central statistical lesson is that a point estimate and its precision must be considered together. The primary mean difference is 0.7, but its recalculated interval extends across zero. The estimate alone might invite an overly simple interpretation; the interval makes clear that the posted summary is compatible with a range of values. A non-significant p-value does not show equivalence, and the sponsor’s equivalence label cannot be fully evaluated without the margin and supporting interval.

The record also illustrates why different statistical procedures can produce related but not identical summaries. The sponsor reports a rank-based analysis, whereas the recalculation uses the posted means and standard deviations. Similar estimates do not remove the need to understand what each procedure analyzes. The secondary outcomes add breadth, but multiple unadjusted comparisons require restraint in interpretation.

Finally, the registry record makes some limitations visible: important details about the analysis population, missing data, multiplicity, and original sample-size planning are not reported. Those gaps do not erase the posted results, but they define how far the conclusions can reasonably extend. Statistical interpretation is strongest when effect estimates, uncertainty, design, analysis choices, and reporting completeness are considered together.

19. 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 registry record leaves important details about the study population unspecified. Although the title refers to chronic kidney disease, the condition is listed as kidney disease, and further information about disease stage, eligibility criteria, baseline uric acid, or other participant characteristics is not reported. The record therefore does not establish how closely the enrolled population represents any narrower clinical subgroup.

Intervention details are limited. Allopurinol is described as a medicine that lowers uric acid, and the comparator is described as placebo tablets without an active ingredient. Dose, treatment duration details beyond the outcome timeframe, adherence, treatment discontinuation, and concomitant care are not reported in the registry record. These omissions limit assessment of treatment exposure and implementation.

The outcome measurement is described as flow-mediated dilation at baseline and week 12, but technical measurement procedures, assessor training, repeatability, and quality control are not reported. The registry also does not report the analysis population, participant flow, reasons for missing data, or the method used to handle missing observations. The group counts in the outcome summaries do not by themselves resolve those questions.

For the sponsor-reported analysis, the method and p-value are stated, but no interval estimate or equivalence margin is provided. The registry does not report a multiplicity strategy for the several outcomes, the original sample-size justification, or details of interim analyses. These limitations are specific to interpreting this registry record; they should not be filled in by assuming standard trial practices. The posted summaries support a descriptive reading of the recorded comparisons but do not permit a full independent audit of the trial’s analysis.

20. Related Tutorials

21. Related Statistical Calculators

22. Sources

• ClinicalTrials.gov: Uric Acid and the Endothelium in CKD — NCT01228903.
• Registry record last updated 2017-06-28; status last verified 2017-05.
• Results first posted 2017-02-23.
• 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.

23. Record Summary

The registry describes a completed randomized, double-masked, parallel-group study sponsored by University of Colorado, Denver. It lists enrollment of 80 and compares allopurinol with placebo in patients with kidney disease. The primary endpoint is change in endothelium-dependent dilation, measured by flow-mediated dilation from baseline to week 12.

The posted primary group means are 0.2 for control and 0.9 for allopurinol. The recalculated unadjusted mean difference is 0.7, with an interval from -1.053 to 2.453 and p = 0.434. The sponsor reports a Wilcoxon (Mann-Whitney) analysis, a net mean difference of 0.7, and p = 0.47, labeled as an equivalence analysis.

The interval around the recalculated primary difference includes zero. The registry record does not report an equivalence margin, a detailed missing-data approach, or a multiplicity strategy. The results are best read as an uncertain comparison of the posted vascular-function summaries, not as proof of equivalence or as evidence about unreported clinical outcomes.