The Impact of Renin-angiotensin System on Brain Activation During Hypoglycaemia in Healthy Men, a PET Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Impact of Renin-angiotensin System on Brain Activation During Hypoglycaemia in Healthy Men, a PET Study (NCT00264641), a non-randomized na study. The primary outcome is Cerebral Activation During Hypoglycaemia.

2. Clinical Question

The study concerns brain activity during hypoglycaemia, assessed with oxygen-15 labelled water PET scanning while participants underwent cognitive function testing. Its focus is whether the activation measure differs according to participants’ basal RAS activity. The record describes RAS as a hormone system involved in regulation of blood pressure and gives the rationale that earlier studies associated high RAS activity with more pronounced cognitive impairment during hypoglycaemia. That rationale is background, not a result of this study.

The research question is observational with respect to RAS group membership: participants were characterized as having high or low basal activity rather than randomly assigned to those categories. The record does not describe a randomized comparison of insulin or another treatment. It also does not report the observed Z score, a group difference, confidence interval, or statistical test result. Therefore, the registry record establishes what the investigators intended to compare, but does not provide a numerical answer to the primary question.

3. Trial Design

The registry record describes a completed, non-randomized, parallel study with no masking. It lists an enrollment of 20 and characterizes the participants as healthy men. The arm descriptions identify 10 healthy men with high basal RAS activity and 10 healthy men with low basal RAS activity. Because group membership was based on RAS activity rather than random allocation, the groups should not be treated as randomized, like-for-like controls.

Human insulin is listed as the intervention. The study summary describes oxygen-15 labelled water PET scanning during hypoglycaemia in response to cognitive function testing. The primary outcome timeframe is after 4 scans on day 1. The registry record does not give detailed procedures for insulin administration, the hypoglycaemia protocol, the cognitive tests, scan timing beyond that timeframe, or how RAS activity was measured and used to classify participants.

The primary outcome is titled “Cerebral Activation During Hypoglycaemia” and uses a Z score. The record says that only between-group analysis data are available, but does not report the numerical outcome or an analysis result. It lists one outcome measure and no analyses. The record does not report the study’s sample-size justification, a prespecified statistical analysis plan, or whether any interim analyses were planned or performed.

The study status is completed. Its start is recorded as 2006-01 and primary completion as 2008-02. These dates describe the registry entry and do not establish when results were analyzed or posted. The comparison is useful to describe as an association between RAS group and cerebral activation in this study population; the non-randomized design does not by itself establish that RAS activity caused any observed difference.

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: Only data available is between group analysis

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 Cerebral Activation During Hypoglycaemia, measured over After 4 scans on day 1.

The primary endpoint is cerebral activation during hypoglycaemia, expressed as a Z score. The registry record states that this score was used to compare the high-RAS-activity group with the low-RAS-activity group. The stated timeframe is after 4 scans on day 1. The study summary links the assessment to oxygen-15 labelled water PET scanning during hypoglycaemia while participants completed cognitive function testing.

A Z score is generally a standardized way to express a measurement relative to a reference distribution. In general, standardization can help express observations on a common scale, but its interpretation depends on how the score and reference distribution are defined. The registry record does not explain the Z-score calculation, its reference distribution, whether higher values indicate more activation, or how scans and cognitive testing contributed to the endpoint. Those details are needed to interpret the direction and magnitude of a particular score.

The record identifies the endpoint and the intended group comparison but does not provide an observed score, group-specific summaries, an effect estimate, or uncertainty interval. Consequently, the endpoint definition indicates what was to be measured, not what the study found or how precisely any group difference was estimated.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry entry identifies a between-group question: whether cerebral activation during hypoglycaemia differs between men with high and low basal RAS activity. The primary measure is a Z score. Interpreting a group comparison ordinarily requires both a definition of the measurement and a statistical summary of how the groups compare. The entry supplies the endpoint name and general comparison, but not the score calculation, observed group values, estimated difference, uncertainty interval, or test result. Thus, the statistical target is described more clearly than the analysis itself.

What does non-randomized mean for the comparison?

Random allocation is a design method intended to make treatment groups comparable, on average, with respect to both measured and unmeasured characteristics. Here, allocation is recorded as non-randomized, and the arms are defined by high or low basal RAS activity. This is not a randomized contrast. Differences in cerebral activation, if estimated, could reflect RAS activity, other differences between the groups, or a combination. Statistical adjustment can sometimes account for measured characteristics, but it cannot automatically remove confounding from unmeasured or poorly measured factors. The registry record does not report adjusted analyses or covariates.

The term parallel indicates that the record describes separate groups, rather than a within-person crossover comparison. That structure affects how observations are related and what statistical model is appropriate. The record does not describe repeated-measure handling, correlations among scans, or whether the primary score is one summary per participant or another unit of analysis. Those choices matter: treating repeated observations as independent when they are related can make uncertainty estimates misleading. The available description is insufficient to determine how this issue was addressed.

What does a Z score communicate?

In general, a Z score expresses a value relative to a reference distribution using a standardized scale. Its meaning depends on the reference and calculation. A score might standardize an individual value, a contrast, or another quantity, and those interpretations are not interchangeable. For this study, the registry says a Z score was used to compare high and low RAS activity, but does not identify its precise construction, sign convention, or reference. Consequently, a reader should not infer what a particular positive or negative value would mean, or how large an effect would be, from the endpoint label alone.

Standardization can be useful when measurements need a common scale, but it does not remove design limitations. A standardized result can still be confounded, imprecise, or sensitive to the selected reference distribution. Reporting the calculation and uncertainty alongside the score would be important for evaluating its statistical and substantive meaning. Those details are not reported in the registry record.

How should uncertainty be assessed?

General statistical interpretation distinguishes an estimate from its uncertainty. An estimate describes the observed contrast under a chosen analysis; an uncertainty interval indicates how much sampling variability is compatible with the data and model. A p-value, when reported, addresses compatibility with a specified null model under assumptions. Neither a p-value nor a confidence interval alone measures clinical importance or proves causation. In this registry entry, there is no posted estimate, confidence interval, or p-value for the primary outcome. The comparison’s direction, magnitude, and precision therefore cannot be assessed from the endpoint description.

The absence of a reported result is not evidence that the groups were equal. It is also not evidence of a statistically significant difference. Both conclusions would require results that the entry does not provide. A complete interpretation would need the group summaries or contrast, an uncertainty measure, and enough methods detail to understand the analysis population and unit of analysis.

What do the sample-size assumptions represent?

The record describes a planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. It says that the effect to detect is a stated fraction of the observed effect. In general, such calculations estimate the participant count that a future study might require under chosen assumptions. They depend on the effect size, variability, allocation, significance threshold, and statistical model. Changing those assumptions can change the planning result.

These illustrations are not the original study’s sample-size justification unless the record explicitly says so; it does not. They are also not observed power. Observed power is not a substitute for reporting an estimated effect and its uncertainty. The registry record does not state the observed effect in its primary outcome description, so the planning assumptions cannot be independently interpreted as evidence about the actual group contrast. Any planning output should be understood as conditional on its assumptions, not as a result of the trial.

Why might over-dispersion matter in general?

For count outcomes, a model may assume a particular relation between the mean and variability. Over-dispersion means the observed variability is greater than that assumption allows. If it is ignored, standard errors can be too small and uncertainty can appear narrower than warranted. This study’s primary outcome is listed as a Z score, not a count outcome, and the registry entry does not report an over-dispersion analysis. The general concept is therefore not a claim about this study; it illustrates why model assumptions need to match the outcome and data structure.

Overall, the registry record permits a description of the planned group comparison and some planning assumptions, but not a reconstruction of the statistical result. The missing score definition, estimate, uncertainty, and analysis details limit independent assessment of the endpoint.

10. Multiplicity, Missing Data and Analysis Populations

The record lists one primary outcome measure and zero analyses. It does not report whether investigators measured additional outcomes, performed exploratory analyses, or considered multiple versions of the primary endpoint. The listed count alone cannot establish that no other statistical tests were conducted. A multiplicity plan—how inference is handled when several outcomes, time points, subgroups, or analyses are considered—is not reported in the registry record.

When multiple statistical comparisons are made, the chance of obtaining an apparently unusual result can increase unless the analysis plan accounts for that multiplicity. This is a general statistical concern, not a conclusion that multiplicity affected this study. Because analysis results and a multiplicity strategy are absent, the entry does not allow readers to evaluate whether the reported inference, if any, was adjusted or selected from several analyses.

The record does not describe missing outcome data, exclusions, withdrawals, or how incomplete scans or tests were handled. The analysis population is also not reported in the registry record. Although the arm descriptions specify 10 men in each group, that alone does not explain whether all enrolled participants contributed to the primary endpoint or whether any observations were unavailable. The record does not state an intention-to-treat, per-protocol, or other analysis-population definition.

These omissions matter because missingness and exclusions can affect both the composition of the analyzed groups and the reliability of the estimated comparison. Without participant flow, missing-data methods, and analysis-population details, the endpoint result cannot be assessed for these sources of uncertainty. None of these details should be inferred from the study’s completed status or from the group descriptions.

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 0% reporting threshold.

The registry lists, for the high-RAS-activity group, 10 at risk and zero serious adverse events, as well as 10 at risk and zero other adverse events. For the low-RAS-activity group, it likewise lists 10 at risk and zero serious adverse events, and 10 at risk and zero other adverse events. These are the posted event counts for the categories recorded.

A zero count means that no events were entered for that category in the registry record. It does not establish that no symptoms or other safety findings occurred, or that all possible events were collected and reported. The record does not provide further details about event definitions, surveillance procedures, duration of follow-up, or completeness of safety reporting. Death counts are not reported in the registry record; they should not be read as zero.

These safety figures do not establish comparative safety. The groups were not randomized, and the entry does not provide a formal safety analysis or uncertainty estimates. The counts are best read narrowly as the adverse-event values recorded for the stated groups, rather than as proof that risk was absent.

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

The registry record documents a study designed to examine cerebral activation during hypoglycaemia in healthy men classified by basal RAS activity. It identifies oxygen-15 labelled water PET scanning, cognitive function testing, a Z-score endpoint, and a between-group comparison. It also records the group definitions and the timeframe after 4 scans on day 1. These details clarify the research question and broad measurement approach.

The primary outcome result itself is not reported in the registry record. There is no numerical score, group contrast, confidence interval, or p-value. Therefore, the posted information does not establish whether cerebral activation differed between the groups, the direction of any difference, its magnitude, or the precision of an estimate. The absence of a result cannot be interpreted as either evidence of no difference or evidence of a difference.

Even if a group difference were reported, the non-randomized design would limit causal interpretation. Group membership was based on basal RAS activity, not random allocation, so other characteristics could contribute to an observed association. The entry does not describe adjustment for potential confounders. The study population is described as healthy men, so the record alone does not establish how findings would apply to other populations or settings.

The safety counts record zero serious and zero other adverse events in each group, but do not establish that no adverse events occurred beyond those categories or that surveillance was complete. Deaths are not reported in the registry record. The most defensible conclusion is therefore about the study’s question and design, not an unreported outcome: the registry describes a physiological comparison but does not provide the numerical evidence needed to judge its result.

13. Why This Trial Matters Statistically

This study is statistically notable because it asks a physiological question through a comparison of groups defined by a biological characteristic rather than randomized treatment assignment. That distinction shapes what the analysis can support. A group contrast can describe an association in the observed participants, but causal interpretation requires attention to other differences between groups. Clear reporting of the design and adjustment strategy is especially important in such comparisons.

The endpoint also illustrates why a measure’s name is not enough to interpret a result. “Cerebral Activation During Hypoglycaemia” and “Z score” identify the topic and scale, but the record does not define the score’s reference or construction. Without that information and a numerical estimate, readers cannot determine what a value means, compare its magnitude with other settings, or evaluate precision.

The registry entry further distinguishes a planned comparison from reported evidence. It lists one outcome measure but no analyses and does not give the primary outcome result. A study can have a clearly stated research question while still leaving readers unable to assess the statistical answer if estimates and uncertainty are absent. Reporting the contrast, analysis population, missing-data handling, and methods would make the findings more interpretable.

Finally, the sample-size assumptions are planning illustrations, not evidence about the observed result or the study’s original design justification. Keeping planning calculations separate from outcome inference helps prevent a sample-size estimate from being mistaken for power or proof of an effect. These points are broadly relevant when evaluating small non-randomized physiological studies, where design, measurement definition, and uncertainty reporting are central to interpretation.

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 principal limitation for statistical interpretation is that the registry record does not report the numerical primary outcome. Without the Z score, group summaries, estimated contrast, or uncertainty interval, the observed association cannot be assessed. The entry also does not report a p-value or other inferential result. This prevents evaluation of both the direction and precision of the comparison.

The non-randomized group assignment is another important limitation. Participants were characterized by high or low basal RAS activity, and the record does not describe adjustment for potential confounding variables. The groups may differ in ways that are associated with cerebral activation, so an observed contrast would not necessarily be attributable to RAS activity alone.

The endpoint’s calculation is not specified. The registry names a Z score but does not state its reference distribution, sign convention, aggregation across scans, or precise relationship to cognitive testing and PET measurements. The record also does not explain the unit of analysis or the handling of potentially related observations across scans.

Additional details needed to assess reliability are not reported in the registry record: participant flow, exclusions, missing outcome data, analysis-population definition, adjustment methods, multiplicity handling, and a complete statistical analysis plan. The sample-size justification for the study is also not reported; the listed planning assumptions do not substitute for it. Finally, the described population is healthy men, limiting the scope of conclusions that can be drawn from this entry about other groups. These limitations concern what can be established from the registry record, not proof that unreported methods were absent.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: The Impact of Renin-angiotensin System on Brain Activation During Hypoglycaemia in Healthy Men, a PET Study — NCT00264641.
• Registry record last updated 2017-03-29; status last verified 2017-03.
• Results first posted 2017-03-29.
• 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, non-randomized, parallel study of cerebral activation during hypoglycaemia in healthy men with high or low basal RAS activity. It lists human insulin, oxygen-15 labelled water PET scanning, cognitive function testing, and a primary Z-score comparison after 4 scans on day 1. The record gives 10 men in each RAS group.

The primary outcome is identified, but its numerical result, effect estimate, uncertainty interval, and statistical test result are not reported. The entry lists one outcome measure and zero analyses. The analysis population, missing-data handling, multiplicity approach, and study sample-size justification are not reported in the registry record. Safety listings show zero serious and zero other adverse events in each group; deaths are not reported. The study’s design and endpoint are described, but the registry information does not provide the results needed to determine the direction, size, or precision of the primary comparison.