Direct Renin Inhibition Effects on Atherosclerotic Biomarkers: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Direct Renin Inhibition Effects on Atherosclerotic Biomarkers (NCT00818779), a randomized phase 4 study. The primary outcome is Plasminogen Activator Inhibitor 1.

2. Clinical Question

3. Trial Design

The registry identifies this as a phase 4, randomized, parallel-group study with no masking. Its official title concerns direct renin inhibition and atherosclerotic biomarkers in patients with stable coronary heart disease and type 2 diabetes mellitus. The sponsor is Texas Tech University Health Sciences Center. The listed enrollment is 38. The record marks the study completed, with a start date of 2008-01 and primary completion of 2011-08.

Participants were assigned to aliskiren or amlodipine. The listed aliskiren dose was 150-300 mg once daily; the listed amlodipine dose was 5-10 mg once daily. The registry describes the primary outcome as change from baseline at six weeks. It also lists four secondary serum measures: vascular cell adhesion molecule, intracellular cell adhesion molecule, C-reactive protein, and nitric oxide.

Randomization is intended, in general, to make treatment groups comparable with respect to both measured and unmeasured characteristics on average. It does not guarantee exact balance in a particular trial, especially in a small study. Because masking is listed as none, participants and study personnel were not masked according to the registry description; the record does not specify whether laboratory staff or outcome assessors were masked separately.

The posted outcome summaries include 16 participants for aliskiren and 15 for amlodipine. These are the arm-specific counts attached to the primary outcome results, not a replacement for the registry's enrollment figure. The record does not explain the relationship between the enrollment and outcome counts, such as whether any participants lacked a measured outcome or were excluded from an analysis.

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

Reasons for not completing this period:

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 Plasminogen Activator Inhibitor 1, measured over 6 weeks (change from baseline).

The primary endpoint was mean change from baseline in serum plasminogen activator inhibitor 1, abbreviated PAI-1 in the registry description, measured at six weeks and reported in ng/ml. PAI-1 is a serum biomarker that indirectly assesses blood-clotting activity. The record says lower PAI-1 levels are thought to be better than higher levels. Because the endpoint is change from baseline, a negative value can represent a decrease and is valid under the definition; the endpoint is not restricted to positive changes.

Biomarkers are used in clinical research as measurable indicators of biological processes. They can help investigators study whether an intervention is associated with a change in a pathway or risk-related measure. A biomarker result is not, by itself, a direct measure of a clinical event or proof of a change in how patients feel or function. The registry record does not report assay procedures, measurement reliability, or a threshold for a clinically important PAI-1 change.

The reported summaries are means with 95% confidence intervals. A mean describes the average observed change in an arm, while a confidence interval conveys uncertainty about that arm-level mean under the statistical model used. The record does not report enough information to determine the model or assumptions underlying those intervals.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry presents a continuous outcome as a mean change from baseline, accompanied by a 95% confidence interval. For a continuous measure, the mean is the arithmetic average of the observed values included in the analysis. Here, the analyzed quantity is change from baseline in PAI-1 at six weeks, rather than the six-week concentration alone. A negative change denotes a decline under this definition, and a positive change denotes an increase.

What does a confidence interval express?

In general, a confidence interval describes the uncertainty around an estimate under a specified statistical procedure and its assumptions. It is not a range containing a fixed proportion of individual participants' measurements. Nor does it mean that every value inside the interval is equally plausible. A narrower interval usually indicates greater precision, while a wider interval indicates less precision. Precision depends on factors such as variation in the measured outcome and the amount of information available.

The two arm-specific intervals reported for this trial both include negative and positive values. This is relevant to interpreting the uncertainty in each mean, but it is not a substitute for an interval around the difference between arms. Two separate confidence intervals do not directly provide the standard error, confidence interval, or p-value for a between-arm contrast. The registry record does not report an estimable comparison for the primary outcome, so no comparative interval should be inferred from the arm summaries.

Why is a direct comparison important?

In a randomized parallel-group study, the treatment question is usually answered by comparing outcomes between assigned groups. A comparison can account for the fact that both groups may change over time, including changes unrelated to treatment. The preferred estimate and method depend on the study plan and the available data. The registry does not report a model, adjustment strategy, or test for the primary contrast. It also does not report a p-value for that contrast. The available means therefore describe each group but do not quantify the difference attributable to assignment.

The registry labels the endpoint as a mean and the dispersion as a 95% confidence interval. It does not specify whether the interval was calculated from a particular distributional method, whether any covariates were included, or whether the analysis used change scores or another model that targets change from baseline. These details matter because different valid methods can produce different estimates and uncertainty, particularly when the sample is limited or the outcome distribution is irregular.

What do the sample-size illustrations mean?

The sample-size material is described as a planning illustration based on the observed effect, rather than as the trial's original design calculation. Its stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. The record does not include the numerical planning results in the information analyzed here, so no sample-size value can be interpreted or repeated.

In general, a planning calculation estimates the number of participants that a hypothetical future study might require under selected assumptions about effect size, variability, significance level, allocation, and desired power. Changing an assumption can change the planning result. When an observed effect is used as the starting point, the result is especially dependent on how well that observed estimate represents the effect a future study seeks to detect. A planning illustration is not evidence that the original trial had a particular probability of detecting an effect. It is not observed power and does not repair the missing comparative analysis.

Normal approximations are mathematical simplifications. Their usefulness depends on whether they are suitable for the outcome and study design. The record's stated assumptions do not establish that a future trial would satisfy them, and the registry does not report the planning calculation's full inputs or numerical output. The illustration should therefore be read as conditional rather than as a definitive recommendation or a description of the original enrollment rationale.

What is the role of randomization and masking?

Random assignment can reduce systematic differences between groups in expectation, but it cannot prevent chance imbalance. In general, masking can reduce some forms of measurement or behavior bias, depending on who is masked and how outcomes are assessed. The registry lists masking as none. It does not report additional masking arrangements for laboratory measurement. The randomized design is a strength for a treatment comparison in principle, but the lack of a posted comparative result prevents readers from evaluating the primary treatment contrast.

The record lists a reported number of analyses as 0 while also posting arm-level outcome summaries. That registry field alone does not clarify how the summaries were generated or whether other analyses were conducted. The analysis method, model specification, and handling of participants without outcome data are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists four secondary outcomes: serum vascular cell adhesion molecule, intracellular cell adhesion molecule, C-reactive protein, and nitric oxide. It also identifies PAI-1 as the primary outcome. When a study examines several outcomes or several comparisons, the chance of at least one apparently notable result can increase if each is assessed without accounting for the number of tests. General approaches to this issue include defining a primary outcome in advance, specifying a testing sequence, or adjusting inference across a family of comparisons.

The registry record does not report whether a multiplicity adjustment was planned or used, how the secondary outcomes were analyzed, or how any secondary findings should be interpreted alongside the primary outcome. No conclusion about an adjustment should be inferred from the outcome list alone. The record also does not provide an estimable primary two-arm comparison, which limits the basis for interpreting the primary result regardless of the approach to secondary outcomes.

Missing-data handling is not reported in the registry record. The primary outcome summaries give arm-specific counts, but the record does not say whether these counts reflect everyone assigned, everyone measured at baseline, everyone with a six-week measurement, or another analysis population. It does not describe reasons for missing measurements, imputation, or sensitivity analyses. The registry record also does not specify whether the primary analysis followed an intention-to-treat principle or another population definition.

These omissions matter because missing outcomes can affect both the estimated mean change and its uncertainty, particularly if the chance of having a measurement is related to treatment or to the outcome itself. The listed enrollment and outcome-specific counts cannot, on their own, establish why counts differ or whether missingness introduced bias. No assumptions about missing data or analysis populations should be attributed to the study without a reported plan.

11. 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 5% reporting threshold.

The adverse-event record lists zero serious adverse events among 16 participants at risk in the aliskiren group and zero among 15 participants at risk in the amlodipine group. It also lists zero other adverse events among 22 participants at risk for aliskiren and zero among 16 at risk for amlodipine. These are the separate denominators and event counts recorded for the two categories; the denominators are not the same across categories.

Zero recorded events means no events of the specified category are listed for those at-risk counts in the registry. It does not establish that the true risk is zero. In general, uncommon harms can remain unobserved in a study, and a small amount of safety information can leave substantial uncertainty about event rates. The difference between the listed at-risk counts also means the figures should not be treated as if they arose from one common safety analysis population. The registry record does not explain the denominator differences.

Deaths are not reported in the registry record. No serious-event terms are listed. These entries should be read as registry reporting, not as proof that no adverse experiences of any kind occurred or that the treatments have equivalent safety. The record does not provide further detail about event definitions, duration of safety follow-up, severity classifications beyond the serious/other grouping, or how events were collected.

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

The posted results show arm-specific mean changes in a serum biomarker at six weeks. The aliskiren group had a reported mean change of 0.65 ng/ml, with a 95% confidence interval from -7.33 to 8.62. The amlodipine group had a reported mean change of 3.82 ng/ml, with a 95% confidence interval from -5.16 to 12.81. Each interval includes values on either side of zero, indicating uncertainty about the direction of the mean change in each group.

Those results do not answer the central comparative question. The registry record does not report an estimable between-arm analysis for the primary endpoint. The two means should not be subtracted to create a new treatment estimate, and their separate confidence intervals should not be used as a formal comparison. No primary comparison p-value, comparative confidence interval, or clinically important threshold is reported. The posted results therefore do not establish whether the groups differed or how precisely a difference was estimated.

The outcome is a biomarker that the record describes as an indirect measure related to clotting activity. A biomarker change does not by itself demonstrate an effect on heart attacks, survival, symptoms, or other patient-important outcomes. The record does not report those outcomes as the focus of this primary result. It also does not provide evidence that a particular PAI-1 change would correspond to a particular clinical benefit or harm.

Likewise, the registry's zero adverse-event counts should be interpreted as the event counts recorded for the stated categories and denominators, not as proof of an absence of risk. The registry record leaves important analytic details unreported, including missing-data handling and analysis populations. Taken together, the posted information offers a limited description of observed biomarker changes and safety counts, but it does not support a definitive conclusion about comparative effects or clinical consequences.

13. Why This Trial Matters Statistically

This study illustrates an important distinction between describing each randomized group and estimating the effect of a treatment relative to its comparator. A mean and confidence interval for each arm can be informative about the observed data in that arm. The treatment question, however, concerns the between-arm contrast. Without a reported contrast and its uncertainty, readers cannot judge the estimated comparative effect using the usual direct statistical evidence.

The distinction is especially useful in small clinical studies. Randomization helps protect against systematic confounding in expectation, but it does not eliminate imprecision or chance imbalance. The arm-specific outcome counts recorded are limited, and both reported confidence intervals extend across zero. General statistical reasoning cautions against treating a non-significant or unavailable comparison as proof of no difference; in this record, no estimable comparison is reported at all.

The trial also illustrates why outcome type matters. PAI-1 is a biomarker used to study a biological process, not a direct clinical endpoint in the information reported. Statistical evidence about a biomarker and evidence about patient-important outcomes answer different questions. Readers need to keep that distinction in view when interpreting a mean change, even when the biomarker is biologically relevant.

Finally, the record shows how registry reporting affects interpretability. Arm-level counts, confidence intervals, and safety entries can be useful, but interpretation also depends on the comparison method, analysis population, missing-data approach, multiplicity plan, and outcome measurement details. Where those items are not reported, the statistical conclusion must remain appropriately limited rather than filling gaps with assumptions.

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.

The main limitation for interpretation is that the registry record does not report an estimable two-arm comparison for the primary continuous endpoint. It gives a mean change and confidence interval for each arm, but not a comparative estimate or its uncertainty. That prevents a direct assessment of the treatment contrast and makes it inappropriate to infer a contrast from the arm-level summaries.

The posted primary outcome summaries have limited precision: both confidence intervals include negative and positive values. The registry does not state a clinically important difference for PAI-1, so the relationship between the range of estimates and clinical relevance cannot be assessed from the record. The measurement is a biomarker, and no linked clinical outcome result is included in the primary endpoint information.

Several details needed to assess potential bias are not reported in the registry record. These include the analysis population, the handling of missing measurements, the reasons for any difference between enrollment and outcome counts, the statistical model, and whether the analyses adjusted for baseline values or other variables. Assay procedures, outcome measurement reliability, adherence, and any separate masking of laboratory assessors are also not described in the information.

The registry lists no masking, which can leave some outcomes vulnerable to measurement or behavior effects in general, although the extent depends on how measurements were collected. The listed at-risk denominators differ between serious and other adverse events, and the record does not explain why. Safety counts therefore offer limited information. Finally, the record does not report a multiplicity approach for the four secondary outcomes or a detailed statistical plan. These omissions constrain interpretation; they do not establish that the study used an inadequate method, only that the method is not reported in the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Direct Renin Inhibition Effects on Atherosclerotic Biomarkers — NCT00818779.
• Registry record last updated 2017-12-05; status last verified 2017-10.
• Results first posted 2012-11-19.
• 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

The registry record describes a completed phase 4, randomized, unmasked, parallel-group study sponsored by Texas Tech University Health Sciences Center. It lists enrollment as 38 and compares aliskiren 150-300 mg once daily with amlodipine 5-10 mg once daily in patients with stable coronary heart disease and type 2 diabetes mellitus.

The primary endpoint was mean change from baseline in serum PAI-1 at six weeks, reported in ng/ml. The arm-specific means were 0.65 for aliskiren and 3.82 for amlodipine, each with a 95% confidence interval spanning negative and positive values. The registry record does not report an estimable two-arm comparison, so the comparative effect and its precision cannot be assessed from the posted primary results.

Four secondary serum outcomes are listed. Safety entries record zero serious adverse events in both arms and zero other adverse events in the stated at-risk groups; deaths are not reported in the registry record. Analysis populations, missing-data handling, and the statistical plan are not reported.