Treatment of Angiotensin Converting Enzyme Inhibitor-induced Angioedema: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Treatment of Angiotensin Converting Enzyme Inhibitor-induced Angioedema (NCT04679311), a randomized phase 2 study. The primary outcome is Determine if Treatment With 2 Units of Fresh Frozen Plasma That Contains ≥ 50 U/L of ACE Activity Increases Serum ACE Activity.

2. Clinical Question

The registry's rationale describes angioedema associated with ACE inhibitors as potentially causing life-threatening airway swelling and states that the trial would test a novel treatment approach. Those statements explain the clinical motivation; they are not evidence of a treatment effect. The posted record contains no measured primary outcome and no reported analysis comparing the interventions.

3. Trial Design

The registry lists this as a phase 2, randomized, single-masked, parallel-group trial. Participants were to receive either high ACE activity fresh frozen plasma or normal saline. The record describes the plasma as 2 units selected to contain ACE activity >= 50 U/L, and the saline as 500 cc. The meaning of single masking, including which people were masked, is not reported in the registry record. The allocation ratio and the procedures used to generate and conceal the allocation are also not reported in the registry record.

Enrollment was 2. The study start date is 2020-12-22, and the primary completion date is 2023-01-31. The overall status is terminated. The reason for termination is not reported in the registry record, so the status alone does not establish why the study stopped or what circumstances affected enrollment or follow-up.

The primary endpoint was planned as a comparison of serum ACE activity before treatment and 30 minutes after treatment. The registry says the blood was never drawn because of pandemic-related issues, leaving no primary result data. The listed secondary outcomes concern angioedema severity assessed with a published validated clinical rating scale and sustained change in serum ACE activity. Their result data are not reported in the registry record.

The record lists three outcome measures and zero analyses. It does not report a statistical analysis plan, the analysis population, the planned handling of missing observations, or whether any interim analyses were planned. These omissions limit what can be inferred about the study's intended statistical procedures. In particular, the randomized design describes how treatment assignment was intended to work, but it cannot produce a treatment-effect estimate when the primary measurements were not collected.

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: Blood was never drawn due to pandemic related issues, the subjects' serum ACE activity were not assessed/drawn prior to treatment and nor 30 minutes after treatment, no result data available.

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.

Population: No patients were randomized to the High ACE FFP. Study was terminated due to end of funding period.

6. Primary Endpoint

The registry lists the primary outcome as Determine if Treatment With 2 Units of Fresh Frozen Plasma That Contains ≥ 50 U/L of ACE Activity Increases Serum ACE Activity, measured over Compare serum ACE activity before treatment and 30 minutes after treatment.

The primary endpoint was intended to measure whether treatment with high ACE activity fresh frozen plasma increased serum ACE activity. Serum ACE activity was to be assessed before treatment and again 30 minutes after treatment. The planned comparison therefore focused on a change in a biological measurement over a defined interval, rather than a direct measure of angioedema severity or airway symptoms.

As general statistical context, a biological measurement can help test a proposed treatment mechanism: researchers can assess whether the measured marker changes in the expected direction after an intervention. Such a marker is not automatically a measure of clinical benefit. Its interpretation depends on the measurement, the clinical context, and how well a change in the marker relates to outcomes that matter to patients. The registry describes separate secondary outcomes addressing angioedema severity and sustained change in serum ACE activity, but no results for those outcomes are reported.

For this trial, the endpoint cannot be evaluated from the posted results. The registry states that blood was never drawn because of pandemic-related issues, so serum ACE activity was not assessed either before treatment or 30 minutes after treatment. There is no observed change, treatment comparison, estimate of precision, or test result for the primary endpoint in the registry record. The endpoint's planned definition remains informative about the research question, but it does not constitute evidence that the biological measurement changed.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What would the randomized comparison estimate?

In general, a randomized trial compares outcomes according to assigned intervention. Random assignment is intended to make the groups comparable, on average, with respect to factors that might otherwise influence the outcome. The registry describes this study as randomized and parallel-group, with high ACE activity fresh frozen plasma and normal saline as the interventions. It does not report the allocation ratio, allocation procedures, or analysis population.

The primary question was about serum ACE activity before treatment and 30 minutes after treatment. A complete analysis would need the measurements and a defined way to compare them, such as estimating change within each group and comparing the groups' changes, or using a model that accounts for baseline measurement. Those are general possibilities, not a description of the trial's actual analysis plan. The specific analysis method is not reported in the registry record. Since the measurements were not collected, no method can recover the primary treatment comparison from the posted results.

What does a confidence interval tell a reader?

In general, a confidence interval expresses uncertainty around an estimated effect under a specified statistical procedure. A narrower interval indicates greater precision in the estimate, while a wider interval indicates more uncertainty. A confidence interval is not the probability that the true effect lies within the particular interval, and it does not establish whether an effect is clinically important. The registry record contains no primary estimate or confidence interval, so no such precision assessment can be made for the primary outcome.

How should significance tests be understood?

In general, a significance test evaluates how compatible the observed data are with a specified null hypothesis under assumptions of the test. A p-value is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. The registry lists zero analyses and provides no primary outcome results or p-value. Statistical significance therefore cannot be assessed from this record. The absence of a reported test is not evidence that a test was negative; the required primary measurements were not collected.

Why do missing measurements matter?

When outcomes are missing, the consequences depend on why they are missing, how much information is absent, and whether the missingness is related to treatment or outcome. General methods for incomplete data rely on assumptions and cannot make absent observations equivalent to observed measurements. In this study, the registry gives a specific reason for the primary blood measurements not being collected: pandemic-related issues. It does not report an imputation method or other analysis of missing primary values. Because the endpoint was not assessed before or after treatment, there is no observed primary change to estimate.

What does the planning illustration mean?

The registry describes sample-size assumptions for planning illustrations: a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. It also says the illustrations are based on a stated fraction of the observed effect, with participant counts per arm for non-time-to-event outcomes. Such calculations are planning scenarios, not observed power and not results from this trial. The registry record does not report an observed primary effect, because the primary blood measurements were not collected. Any planning illustration should therefore not be mistaken for evidence that the trial detected an effect or had a particular ability to detect one.

In general, power is a design-stage probability tied to assumptions about an effect, variability, allocation, and analysis. It does not describe whether a treatment effect was observed. The registry's planning assumptions do not substitute for primary results, and no additional sample-size justification or protocol rationale is reported in the registry record.

Why can over-dispersion matter?

In general, over-dispersion occurs when count data vary more than a statistical model assumes. If ignored, standard errors can be too small and confidence intervals too narrow, making evidence appear more precise than it is. This is a general issue for some count-outcome analyses; the registry record does not report an analysis of count outcomes or a model that would require an over-dispersion assessment. It is not possible to infer that such a model was used.

More broadly, the registry does not report the statistical analysis plan, estimand, model specification, adjustment variables, treatment of protocol deviations, interim analyses, or multiplicity procedure. Those are not details that can be reconstructed from the randomized label or from the endpoint description. The result record remains the deciding source for what was measured and analyzed: it reports no primary blood measurements and zero analyses.

10. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when a study evaluates several outcomes, time points, treatment contrasts, or statistical tests. In general, the more tests considered, the greater the chance of at least one apparently unusual result under a collection of null hypotheses. Researchers may address this through a prespecified testing hierarchy, adjustment procedures, or a clearly stated distinction between primary and exploratory analyses. The specific approach depends on the design and research question.

The registry identifies one primary outcome and lists secondary outcomes concerning angioedema severity assessed with a published validated clinical rating scale and sustained change in serum ACE activity. It lists three outcome measures and zero analyses. No multiplicity adjustment or testing hierarchy is reported in the registry record. Since no outcome results or analyses are reported, there are no observed tests to evaluate for multiplicity in the posted results.

The record states that the primary blood measurements were not collected because of pandemic-related issues. It does not report results for the listed secondary outcomes or explain whether they were collected. The reason for any missing secondary outcome data is not reported in the registry record. It also does not describe an imputation procedure or other missing-data analysis.

The analysis population is not reported in the registry record. There is no information about whether an intention-to-treat, per-protocol, or other population was planned or used. The record also does not report exclusions, adherence, or participant-level analysis details. These gaps prevent assessment of how any analyses might have handled random assignment, missing observations, or multiple outcomes. They do not alter the key result status: no primary outcome data or analyses are available in the registry record.

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.

The registry's adverse-event record lists the high ACE activity fresh frozen plasma arm with zero participants at risk for the recorded serious-event and other-event categories, zero affected, and zero deaths. For the normal saline arm, it lists 2 at risk in each of those categories, zero affected, and zero deaths. No top serious-event terms are listed.

These are registry counts, not a comparative estimate of risk. In particular, zero listed at risk in the plasma arm means the entry does not provide an exposed group from which to assess event frequency. In the saline arm, zero affected is a count within the listed at-risk group; it does not demonstrate that the intervention has no risk. The record does not provide further detail about event definitions, ascertainment procedures, observation duration, or the relationship between these safety entries and treatment exposure.

In general, an absence of recorded events is not the same as evidence that an event cannot occur. Safety comparisons require interpretable exposure and follow-up information in each group, alongside clear definitions and systematic reporting. Given the registry entries and the limited enrollment, the safety record does not support a reliable comparative conclusion about serious or other adverse events.

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

The registry record establishes that a randomized, single-masked, parallel-group phase 2 trial was registered to compare high ACE activity fresh frozen plasma with normal saline for ACE inhibitor-induced angioedema. Its primary question was whether the plasma treatment increased serum ACE activity, measured before treatment and 30 minutes after treatment. The record also identifies secondary outcomes related to angioedema severity and sustained serum ACE activity.

What the result record does not establish is whether serum ACE activity increased, whether angioedema severity changed, or whether the interventions differed on any outcome. The primary blood samples were never drawn because of pandemic-related issues, and no primary result data are available. The record lists zero analyses and reports no secondary outcome results. There is therefore no treatment-effect estimate, confidence interval, or test result to interpret.

In general, a planned biological endpoint can address whether a treatment is associated with a change in a proposed marker. Even when measured, a change in a marker is not automatically evidence of a change in symptoms or other clinical outcomes. The registry listed a separate clinical rating-scale outcome, but does not report its results. The proposed research question and the observed evidence must remain distinct.

Likewise, a randomized label describes the intended assignment design, not a demonstrated effect. Randomization is useful for comparing measured outcomes, but it cannot compensate for absent outcome measurements. The safety counts do not fill that gap: the plasma arm has zero participants listed at risk, and the saline arm has zero recorded events among 2 listed at risk. Those entries do not establish comparative safety.

The appropriate interpretation is limited to the documented design, enrollment, termination status, missing primary measurements, and recorded adverse-event counts. The record does not show that treatment worked or failed. It leaves the primary clinical and biological questions unanswered.

13. Why This Trial Matters Statistically

This trial matters statistically because it illustrates the difference between a research question and an analyzable result. The registry describes a randomized comparison intended to evaluate serum ACE activity after treatment, but the primary measurements were not collected. Without outcome data, no effect estimate can be calculated from the posted record, and uncertainty about an effect cannot be quantified with a confidence interval.

The case also shows why planned design features do not guarantee an informative treatment comparison. Randomization and masking can support a valid comparison when outcomes are collected and analyzed as intended. Here, the endpoint's absence prevents the comparison from answering its primary question. A planned sample-size illustration cannot replace observed data or demonstrate that an effect was detected.

Missingness has a concrete, reported context: the registry attributes the absent blood draws to pandemic-related issues. That explanation is relevant to understanding why the planned endpoint is unavailable, but it does not supply the measurements or eliminate the resulting uncertainty. The secondary outcomes and their results are not reported, so they cannot be used to resolve the primary endpoint's absence.

The safety record is another useful reminder that counts need denominators and exposure context. A zero event count in an arm with zero participants listed at risk is not a comparative safety finding. The saline entries also require restraint: zero recorded events among 2 listed at risk do not establish absence of risk.

For biostatistical interpretation, the most informative conclusion is sometimes that the record cannot support an effect estimate. Separating intended analyses from observed data helps prevent a trial's rationale, design, or planned endpoint from being mistaken for evidence about treatment effects.

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 is that the primary endpoint was not measured. The registry states that blood was never drawn because of pandemic-related issues, and no serum ACE activity results are available before treatment or 30 minutes after treatment. This prevents estimation of the planned primary outcome and leaves its direction, magnitude, and precision unknown.

Enrollment was 2, and the study is listed as terminated. The reason for termination is not reported in the registry record. The record does not provide participant characteristics, treatment assignments, allocation ratio, or details about follow-up, so the small enrollment cannot be interpreted further as a completed comparison between the planned arms.

Secondary outcome results are not reported. The registry names an angioedema severity rating-scale outcome and sustained change in serum ACE activity, but does not provide observations or analyses for them. It is not reported in the registry record whether these outcomes were assessed or why their results are absent.

Important design and analysis details are also not reported in the registry record, including the identity of the masked parties, allocation procedures, analysis population, statistical analysis plan, handling of missing data, and multiplicity approach. The registry lists zero analyses. The adverse-event entries have zero participants at risk in the plasma arm and limited at-risk entries in the saline arm, which precludes a meaningful safety comparison from these counts.

These limitations mean the record describes the intended trial question more clearly than it documents an answer. It does not establish an effect in either direction.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Treatment of Angiotensin Converting Enzyme Inhibitor-induced Angioedema — NCT04679311.
• Registry record last updated 2024-03-27; status last verified 2024-02.
• Results first posted 2024-03-27.
• 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

NCT04679311 is a randomized, single-masked, parallel-group phase 2 trial listed as terminated. It studied high ACE activity fresh frozen plasma versus normal saline for angioedema caused by an angiotensin-converting-enzyme inhibitor. Enrollment was 2. The study start date is 2020-12-22, and the primary completion date is 2023-01-31.

The primary outcome was intended to assess serum ACE activity before treatment and 30 minutes after treatment. The registry states that blood was never drawn because of pandemic-related issues, and no primary result data are available. Listed secondary outcomes concern angioedema severity and sustained change in serum ACE activity; results are not reported. The registry lists zero analyses.

The adverse-event record lists zero participants at risk in the plasma arm and 2 at risk in the saline arm, with zero affected and zero deaths in the listed categories. These counts do not establish comparative safety. The registry record documents the study's design and missing primary measurements, but does not provide an efficacy result.