This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Calf Deep Vein Thrombosis Treatment Trial (NCT03590743), a randomized phase 4 study. The primary outcome is Number of Subjects Who Experience a Composite Venous Thromboembolism (VTE) Event Within 3 Months.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03590743 |
| Phase | Phase 4 |
| Condition | Deep Vein Thrombosis |
| Allocation | Randomized |
| Design model | Single Group |
| Masking | Quadruple |
| Enrollment | 5 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Mayo Clinic |
| Results posted | Yes |
2. Clinical Question
Population
People with isolated calf vein thrombosis, a form of deep vein thrombosis affecting calf veins. The registry record reports enrollment of 5 participants before the study was terminated because of lack of subject enrollment.
Intervention
Apixaban, described as 10 mg twice daily for 7 days followed by 5 mg twice daily for 3 months.
Comparator
The study objective describes comparison with serial imaging of the deep vein thrombosis. The intervention listing also names matching placebo; how placebo relates to the serial-imaging strategy is not reported in the registry record.
Primary question
Whether the apixaban strategy reduces the risk of a composite venous thromboembolism event within 3 months of therapy initiation, compared with the intended alternative strategy.
The primary outcome combines thrombus propagation within calf veins or into proximal deep veins, symptomatic or incidental venous thromboembolism recurrence, and all-cause mortality. The registry describes independent, blinded central adjudication of suspected venous thromboembolism events. That process is intended to assess suspected events consistently without knowledge of treatment assignment.
The clinical question is therefore about a treatment strategy and a composite of several types of events, not about one isolated symptom or imaging finding. The record also lists mean time of thrombus propagation and net clinical benefit or harm among the secondary outcomes. However, the registry states that the study was terminated because of lack of subject enrollment and that data were not analyzed. It does not report an estimate comparing the strategies, so the clinical question remains unanswered by the posted results.
3. Trial Design
The registry describes a Phase IV, randomized, quadruple-masked study sponsored by Mayo Clinic. It lists apixaban and matching placebo as interventions, and gives a single-group model classification despite also identifying random allocation and listing two intervention names. This inconsistency in the registry description should be kept in mind when interpreting the intended design. The record does not clarify how the placebo listing relates to the objective’s comparison with serial imaging.
The planned apixaban regimen was 10 mg twice daily for 7 days, followed by 5 mg twice daily for 3 months. The placebo description says participants would receive matching placebo. The primary outcome timeframe was within 3 months of therapy initiation. The study’s brief summary describes prevention of thrombus spread, pulmonary embolism, and recurrent deep vein thrombosis as the objective of the strategy comparison.
The record gives a study start date of 2019-02-19 and a primary completion date of 2019-06-03. Its status is terminated, with the stated reason being lack of subject enrollment. Enrollment was 5. The primary outcome description explicitly says that data were not analyzed. No primary outcome estimate or inferential comparison is reported.
Random allocation is generally used to reduce systematic differences between assigned groups, while masking is generally intended to limit the influence of treatment knowledge on care, outcome assessment, or reporting. Those design features do not by themselves ensure that a treatment comparison can be estimated: adequate enrollment, outcome data, and a reported analysis are also needed. The record does not report details of the randomization procedure, allocation concealment, implementation of masking, or the planned statistical analysis. These details are 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
| Stage | Apixaban | Placebo |
|---|---|---|
| STARTED | 2 | 3 |
| COMPLETED | 2 | 2 |
| NOT COMPLETED | 0 | 1 |
Reasons for not completing this period:
| Reason | Apixaban | Placebo |
|---|---|---|
| Withdrawal by Subject | 0 | 1 |
Analysis population for the primary outcome, as defined in the registry: Study terminated due to lack of subject enrollment. Data was not analyzed.
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.
| Characteristic | Unit | Apixaban | Placebo | Total |
|---|---|---|---|---|
| Participants analysed | 2 | 3 | 5 | |
| Age, Continuous | years | 77 (SD 9.9) | 60 (SD 17.69) | 67.3 (SD 16.36) |
| Sex: Female, Male: Female | Participants | 2 | 1 | 3 |
| Sex: Female, Male: Male | Participants | 0 | 2 | 2 |
| Race and Ethnicity Not Collected | Participants | — | — | 0 |
| Region of Enrollment: United States | participants | 2 | 3 | 5 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Subjects Who Experience a Composite Venous Thromboembolism (VTE) Event Within 3 Months, measured over Within 3 months of therapy initiation.
| Element | Registry entry |
|---|---|
| Result type | N/A |
| Measure of spread | not applicable |
| Unit | not stated |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is the number of subjects who experience a composite venous thromboembolism event within 3 months of therapy initiation. The composite includes propagation of thrombus within the calf veins or into proximal deep veins, symptomatic or incidental venous thromboembolism recurrence, and all-cause mortality. Suspected venous thromboembolism events were to be evaluated by a central, blinded, independent adjudication committee.
Composite endpoints are used generally to capture multiple clinically relevant event types under a shared outcome definition. They can represent a broader range of events than any single component, but the combined result may be difficult to interpret without knowing which components occurred. Components may differ in clinical importance, frequency, or how they are detected. A total composite count does not by itself reveal the contribution of each component.
In this record, the endpoint definition and timeframe are described, but the primary outcome was not analyzed. No number of participants with the composite event, component-specific results, treatment contrast, or uncertainty interval is reported. The endpoint therefore identifies what the trial intended to assess, rather than documenting an observed comparison between strategies.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The central interpretive fact is that the study was terminated because of lack of subject enrollment and the registry states that the data were not analyzed. Enrollment was 5. Consequently, the posted record does not provide an analyzed primary outcome result or a statistical comparison of apixaban with the intended alternative. It cannot establish the direction or size of a treatment effect, or how precisely such an effect might have been estimated.
The intervention listing reports 2 participants at risk for serious adverse events in the apixaban group and 3 in the placebo group. It reports 0 participants with serious adverse events in either group. The record also reports other adverse events among 2 participants at risk in the apixaban group and among 0 participants at risk in the placebo group. Deaths are reported as 0 in both groups. These descriptive safety counts do not replace an analysis of the primary endpoint, and the small numbers do not support a stable comparative conclusion.
The record lists 4 outcome measures and 0 analyses. It names mean time of thrombus propagation and net clinical benefit or harm as secondary outcomes, but does not report analyzed results for those outcomes. The primary outcome is a composite with several event types; without component results, even an analyzed composite would not alone show which event types accounted for a difference. In this record, no composite comparison is available at all.
Confidence intervals describe the range of effect estimates compatible with observed data and a statistical model. A narrow interval generally indicates greater precision, while a wide interval indicates substantial uncertainty. No primary effect estimate or confidence interval is reported, so precision cannot be assessed from the primary outcome. The absence of an estimate is not evidence that the strategies have equal outcomes; it means that the record does not supply an analyzed comparison.
Any sample-size planning illustrations should be read as hypothetical planning quantities, not as observed power or evidence about the trial’s result. The registry record does not report an analyzed treatment effect for the primary endpoint, and no sample-size justification for the trial is reported. A planning calculation based on an effect assumption cannot recover a treatment effect from an unanalysed study.
Overall, the record describes the intended question and some descriptive adverse-event counts, but it does not answer the efficacy question. It also does not provide enough information to assess the completeness of outcome ascertainment, the handling of missing data, or the statistical uncertainty around a treatment comparison.
9. Statistical Methods Explained
What would a randomized comparison estimate?
In general, a randomized trial compares outcomes according to the groups participants were assigned to. The interpretation depends on the specific outcome definition, the follow-up period, and the analysis population. A treatment contrast is an estimate of how outcomes differed between assigned strategies; it is not the same as simply describing what happened in one group. Randomization can support a fair comparison when assignment is implemented as planned and outcome data are sufficiently complete, but it does not guarantee that a comparison will be reported or precise.
For this study, the intended primary comparison concerns a composite venous thromboembolism event within 3 months of therapy initiation. The registry record does not report an analysis of that outcome. It therefore supplies no estimated contrast, standard error, confidence interval, or hypothesis-test result for the primary question. Those quantities cannot be inferred from the design description or the descriptive safety counts.
How should the composite endpoint be understood?
A composite endpoint combines different events into a single outcome definition. This can be useful when the study aims to assess a range of related outcomes, as the registry’s definition does by including thrombus propagation, recurrent venous thromboembolism, and all-cause mortality. In general, the composite can increase the number of events available for analysis relative to a narrower endpoint. However, a composite estimate does not automatically mean that each component behaves similarly or has the same importance.
Interpretation usually benefits from component-level results as well as the combined result. For example, readers would want to know how events were distributed across propagation, recurrence, and mortality, and whether those component results were assessed consistently. The registry describes blinded central adjudication for suspected venous thromboembolism events, but does not report an analysis of the composite or its components. Thus, no component pattern can be assessed from the posted results.
What do masking and adjudication contribute?
As a general statistical and trial-design principle, masking can reduce the risk that knowledge of assigned treatment affects participant behavior, clinical decisions, or outcome assessment. Independent adjudication can support consistent classification of suspected events under prespecified definitions. These safeguards can improve the credibility of outcome measurement, but they cannot compensate for an outcome analysis that was not performed or reported.
The registry identifies the study as quadruple masked and describes a central, blinded, independent adjudication committee. It does not explain which roles were masked, how masking was maintained, or the adjudication procedures beyond that description. Those details are not reported in the registry record.
What do estimates and confidence intervals tell readers?
In general, an effect estimate summarizes the observed difference or relationship defined by an analysis. A confidence interval communicates statistical uncertainty around that estimate under the analysis assumptions. The estimate addresses the direction and magnitude of the observed contrast; the interval indicates how precisely it has been estimated. Neither a confidence interval nor a p-value can make an inadequately described or unanalysed outcome informative.
No primary estimate, confidence interval, or p-value is reported. The registry lists 0 analyses and states that data were not analyzed. As a result, there is no primary efficacy statistic to interpret and no statistical evidence in the record for or against a difference between the intended strategies.
How should sample-size planning illustrations be read?
Sample-size calculations are generally planning tools. They describe how many participants might be needed under chosen assumptions about the effect to detect, variability or event rates, significance level, allocation, and analysis method. Such calculations are conditional on their assumptions; they are not results from participants in the trial and do not show whether an observed effect is real.
The registry’s planning description says that its illustrations use a two-sided significance level of 0.05, equal allocation, a normal approximation, and an effect defined as a fraction of an observed effect. For time-to-event planning, it describes total events; for other planning calculations, it describes participants per arm. These are planning conventions, not observed trial outcomes. The record does not report the trial’s own sample-size justification. Since the primary outcome was not analyzed, any planning figures should not be treated as an estimate of treatment benefit, observed power, or a substitute for the missing comparison.
What is not available for statistical assessment?
The registry does not report the statistical analysis plan, the populations used for analysis, how missing data would be handled, or whether interim analyses were planned or performed. These items are not reported in the registry record. In general, they matter because analysis choices can affect which participants contribute to an estimate, how incomplete follow-up is addressed, and how uncertainty is quantified. Without a reported analysis and its methods, readers cannot evaluate those choices for this study.
10. Multiplicity, Missing Data and Analysis Populations
Multiplicity arises when a study assesses several outcomes, comparisons, time points, or analyses. In general, conducting many statistical tests can increase the chance of at least one apparently notable result arising by chance. Prespecified priorities and appropriate interpretation help readers understand how multiple findings relate to the main question. The registry lists 4 outcome measures, including the primary composite outcome and secondary outcomes for mean time of thrombus propagation and net clinical benefit or harm. It reports 0 analyses, so there are no posted statistical tests or estimates from which to assess multiplicity adjustments or the interpretation of multiple findings.
The primary outcome itself combines several event categories. The registry record does not reduce it to a single comparison, and does not report results for the composite or its individual components. No multiplicity procedure is described. Whether such a procedure was planned is not reported in the registry record.
Missing-data methods and analysis populations are also not reported in the registry record. In general, missing outcome information can affect estimates if participants with unavailable outcomes differ systematically from those with observed outcomes. An analysis population definition indicates which randomized or enrolled participants are included in a given analysis. Without reported methods or an analyzed endpoint, it is not possible to determine how missing observations or participant inclusion would have been handled.
The record says that data were not analyzed because the study was terminated due to lack of subject enrollment. It does not report interim analyses or a statistical plan. These omissions should be distinguished from evidence of a particular analysis choice: the registry does not establish what methods were planned or whether any were applied.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Apixaban | 0 | 2 | 0.0% |
| Placebo | 0 | 3 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Apixaban | 0 of 2 |
| Placebo | 0 of 3 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Apixaban | 2 of 2 |
| Placebo | 0 of 3 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Apixaban | Placebo |
|---|---|---|---|
| Nose Bleed | Vascular disorders | 2 of 2 | 0 of 3 |
| Shortness of Breath | Respiratory, thoracic and mediastinal disorders | 1 of 2 | 0 of 3 |
The registry reports serious adverse events for 2 participants at risk in the apixaban group and 3 in the placebo group. It reports 0 participants affected by serious adverse events in each group. Deaths are reported as 0 in each group. The record lists no serious adverse event terms.
For other adverse events, the record reports 2 affected participants among 2 at risk in the apixaban group and 0 affected participants among 3 at risk in the placebo group. These are descriptive counts. They do not constitute an adjusted or inferential comparison, and the registry does not report an analysis of these figures.
In general, safety counts should be interpreted with attention to the number of participants observed, the duration and completeness of follow-up, event definitions, and whether events are counts of people or repeated events. The posted figures identify participants affected, but the registry record does not provide event-level descriptions for the other adverse events or further information on follow-up completeness. With enrollment of 5 and no reported safety analysis, the figures are too limited to support a stable comparative assessment. The absence of reported serious adverse events in these groups should not be read as proof that serious events cannot occur.
12. What the Result Does, and Does Not, Mean
The record documents an intended randomized, quadruple-masked study of apixaban for isolated calf vein thrombosis, with a primary outcome defined as a composite venous thromboembolism event within 3 months of therapy initiation. It also documents that the study was terminated because of lack of subject enrollment and that the primary data were not analyzed. These registry entries define what the registry can and cannot say.
The record does not show whether apixaban changed the risk of the primary composite outcome relative to the intended alternative strategy. It contains no primary estimate, confidence interval, or test result. No conclusion about the direction, magnitude, or precision of an efficacy difference can be drawn. The lack of an analyzed result is not evidence that the strategies are equivalent, and it does not demonstrate that either strategy is better.
The adverse-event section contains descriptive counts, including no reported serious adverse events or deaths in either listed group, and other adverse events in the apixaban group. Given the enrollment and absence of a reported analysis, those counts cannot establish a comparative safety profile. They also do not answer the primary efficacy question.
More generally, a trial’s design can define a useful clinical question without yielding an answer if enrollment ends before an informative analysis is available. A planned comparison, a sample-size illustration, and a treatment-effect result are different things. Planning quantities describe hypothetical assumptions; treatment-effect estimates require analyzed outcome data. The registry record reports the former type of information but not the latter.
The appropriate reading is therefore limited: the study aimed to compare strategies for isolated calf vein thrombosis, but its posted results do not provide an analyzed comparison. The record is informative about the trial’s stated objective, design features, termination, and a small set of adverse-event counts, while leaving the efficacy question unresolved.
13. Why This Trial Matters Statistically
This trial matters statistically because it illustrates the difference between a well-defined research question and an answer supported by analyzed data. The registry specifies a population, an intervention, a comparator framing, a composite outcome, and a follow-up timeframe. Yet it also records termination for lack of subject enrollment and states that the data were not analyzed. A clearly described endpoint is not itself evidence of an effect.
The enrollment of 5 also draws attention to precision. In general, estimates based on limited information tend to be uncertain, and sparse event data can make comparisons especially unstable. In this case, the primary endpoint was not analyzed, so there is no estimate whose precision can be evaluated. The descriptive adverse-event counts should not be mistaken for a formal treatment comparison.
The composite outcome raises a further general issue: an overall result, when available, needs component-level context. Thrombus propagation, recurrence, and all-cause mortality are different event types. Their combined definition may serve the trial’s objective, but a composite alone would not reveal how each component contributed. The record does not report analyzed composite or component results.
The record also shows why planning illustrations should be kept separate from observed findings. Sample-size planning depends on assumptions and is intended to guide design; it is not observed power and cannot replace an outcome analysis. Here, the registry does not report the trial’s own sample-size justification or a primary treatment-effect estimate.
For clinical researchers and biostatisticians, the key lesson is one of disciplined interpretation: report what the registry documents, distinguish descriptive counts from inferential comparisons, and treat missing analyses as unresolved evidence rather than as a null finding.
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 most important limitation is that the study was terminated because of lack of subject enrollment and the registry states that data were not analyzed. Enrollment was 5, and no primary treatment-effect estimate is reported. The record therefore cannot support an efficacy comparison or an assessment of its precision.
The registry’s design descriptions are not fully aligned: it identifies random allocation and quadruple masking, lists apixaban and placebo interventions, and also classifies the study as a single-group model. The objective describes comparison with serial imaging, while the intervention listing names matching placebo. How these descriptions fit together is not reported in the registry record. This leaves uncertainty about the exact intended comparator and analysis structure.
The outcome is a composite of thrombus propagation, venous thromboembolism recurrence, and all-cause mortality. No analyzed composite or component results are available. The record also does not report the statistical analysis plan, analysis populations, missing-data methods, sample-size justification, or interim analysis procedures. These details are not reported in the registry record.
The adverse-event figures are limited to small descriptive counts, with no serious adverse events or deaths reported in either listed group and other adverse events reported in the apixaban group. The record does not supply event-level descriptions for those other events or an inferential safety comparison. These limitations constrain interpretation of both efficacy and safety, but should not be filled in by assumptions about procedures that the registry does not describe.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Calf Deep Vein Thrombosis Treatment Trial — NCT03590743.
- Registry record last updated 2020-03-25; status last verified 2020-03.
- Results first posted 2020-03-25.
- 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.
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18. Record Summary
The registry record describes NCT03590743, a Phase IV study sponsored by Mayo Clinic that aimed to evaluate apixaban for isolated calf vein thrombosis. It identifies random allocation and quadruple masking, lists apixaban and matching placebo, and gives the apixaban regimen as 10 mg twice daily for 7 days followed by 5 mg twice daily for 3 months. The objective describes comparison with serial imaging.
The primary outcome was a composite venous thromboembolism event within 3 months of therapy initiation, including thrombus propagation, recurrent venous thromboembolism, or all-cause mortality. The study was terminated because of lack of subject enrollment, with enrollment of 5. The registry states that data were not analyzed and lists 0 analyses. Descriptive adverse-event counts are reported, but no analyzed primary outcome or treatment-effect estimate is available.