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 Using Intravenous Heparin Versus Standard of Care Subcutaneous Heparin to Prevent Clots After Surgery (NCT01608906), a randomized na study. The primary outcome is Development of DVT (Deep Vein Thrombosis).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01608906 |
| Phase | NA |
| Condition | Venous Thrombosis |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 152 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University of Colorado, Denver |
| Results posted | Yes |
2. Clinical Question
The trial was designed to compare two approaches to preventing venous clots in patients receiving intensive care: a continuous low-dose intravenous heparin infusion and subcutaneous heparin used as standard of care. The clinical question was whether the intravenous strategy was associated with a different occurrence of deep vein thrombosis (DVT) during follow-up. The registry record does not report the outcome results needed to answer that question.
Population
Patients in an intensive care unit who were enrolled in the randomized trial. The registry describes the study population as patients at risk of venous clots, but detailed eligibility criteria are not reported in the registry record.
Intervention
A continuous low-dose intravenous heparin infusion, titrated to a PTT of 40-45.
Comparator
Subcutaneous heparin 5000 units 3 times/day, described as standard of care.
Primary question
How did the occurrence of DVT from the start of study intervention through 6 months compare between the randomized treatment strategies? The registry record gives no outcome measure data with which to estimate that comparison.
The primary endpoint focused on DVT, while pulmonary embolism and sepsis were listed as secondary outcomes. The trial’s stated purpose was prevention of clots after surgery in the intensive care setting. However, the registry does not report enough detail to determine which enrolled patients had undergone surgery or how the enrolled population differed from other intensive care patients.
3. Trial Design
The registry describes a randomized, parallel-group trial with no masking. Random assignment is intended to make treatment groups comparable, on average, with respect to measured and unmeasured factors at the time of assignment. It does not guarantee that the groups will be identical, and the record does not report how the random sequence was generated or how assignment was concealed.
The planned comparison was continuous low-dose intravenous heparin versus subcutaneous heparin. The intravenous infusion was titrated to a PTT of 40-45. The comparator was subcutaneous heparin 5000 units 3 times/day and was identified as standard of care. The registry lists enrollment as 152. That is the recorded enrollment figure; the record does not report how many participants were assigned to each strategy or how many contributed outcome data.
The trial status is completed. Its recorded start is 2007-05 and its primary completion is 2014-05. The registry lists the study phase as NA. These design and status details describe the planned and recorded conduct of the trial, but they do not supply evidence about whether either strategy changed DVT occurrence.
Because masking was listed as none, participants and study personnel were not described as masked to treatment assignment. The registry does not report whether outcome assessors were masked. This distinction matters because knowledge of treatment assignment can affect care or ascertainment, although the record does not establish that such effects occurred. The DVT diagnosis approach also changed during the study: screening ultrasound was planned for the first 70 patients on study days 0 and 5, while later diagnoses were to follow standard care. Further details about implementation and adherence are not reported in the registry record.
The registry does not report a statistical analysis plan, allocation ratio, sequence-generation method, or sample-size justification. The listed planning assumptions are not a record of the trial’s original design rationale. With no outcome data available, the design alone cannot show the direction or size of a treatment 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.
Before assignment: PI left the university in 2013. Numerous attempts were made to contact the PI and study team members, but efforts were unsuccessful. Arms are combined because no data is available regarding how participants were assigned to each study arm.
Overall Study
| Stage | All Participants |
|---|---|
| STARTED | 152 |
| COMPLETED | 113 |
| NOT COMPLETED | 39 |
Analysis population for the primary outcome, as defined in the registry: PI left the university in 2013. Numerous attempts were made to contact the PI and study team members, but efforts were unsuccessful. No outcome measure data is 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: PI left the university in 2013. Numerous attempts were made to contact the PI and study team members, but efforts were unsuccessful. Arms are combined because no data is available regarding how participants were assigned to each study arm.
| Characteristic | Unit | All Participants |
|---|---|---|
| Participants analysed | 152 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 152 |
| Age, Categorical: >=65 years | Participants | 0 |
| Sex: Female, Male: Female | Participants | 68 |
| Sex: Female, Male: Male | Participants | 84 |
| Region of Enrollment: United States | participants | 152 |
6. Primary Endpoint
The registry lists the primary outcome as Development of DVT (Deep Vein Thrombosis), measured over from start of study intervention to 6 months.
| 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 was development of deep vein thrombosis. DVT is a clot in a deep vein and is a clinically relevant measure for a trial intended to prevent venous thromboembolism. The registry describes follow-up from the start of study intervention to 6 months.
Ascertainment was planned in stages. For the first 70 patients, ultrasound screening for DVT was to occur on study days 0 and 5. After day 5, and for all remaining subjects, DVT was to be diagnosed according to standard of care by the attending physician. New DVT incidences were to be recorded daily until hospital discharge or for a maximum of 28 days. DVT diagnosis was also to be collected at 6 months from the primary care physician’s office or the patient’s household.
These details indicate that the endpoint could be identified through scheduled ultrasound, clinical diagnosis, and later follow-up. Different ascertainment routes can affect how often events are detected, especially when one route actively screens for a condition and another relies on usual clinical diagnosis. The registry does not report how consistently these procedures were carried out or how diagnoses were confirmed.
Most importantly, the registry states that no outcome measure data are available. It therefore does not report the number of DVT events, a comparison between strategies, or an estimate of precision for the primary endpoint. The endpoint’s definition and follow-up plan describe what the study intended to measure, not what the study found.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The central interpretive limitation is that the registry record contains no primary outcome results. It gives no DVT event counts by treatment strategy, no effect estimate, and no confidence interval or p-value. Without those results, the comparative effect of intravenous and subcutaneous heparin cannot be estimated from this record. The planned randomized design does not replace the missing outcome evidence.
The record reports enrollment of 152 and describes two treatment approaches, but it does not report the number assigned to each approach, the number followed for the endpoint, or the number included in any analysis. Those quantities are needed to understand the information available for a treatment comparison. A confidence interval, in general, expresses the precision of an effect estimate; no such interval is reported for DVT. It is therefore not possible to judge whether a hypothetical estimate would have been precise or uncertain.
The outcome’s ascertainment plan is relevant to interpretation. Ultrasound screening was planned on study days 0 and 5 for the first 70 patients. Later diagnosis was to follow standard care, with daily recording until discharge or a maximum of 28 days and additional collection at 6 months. Active screening and usual clinical diagnosis may identify events differently. The registry does not report whether this change in ascertainment affected event detection or whether the approach was applied as planned.
Other listed outcomes were pulmonary embolism and sepsis. The registry does not report results for these outcomes either, nor does it report an analysis accounting for multiple outcomes. The primary endpoint description includes multiple ascertainment periods and methods, but there is no reported analysis that reduces these into a single comparison. No particular interpretation of secondary outcomes or follow-up periods can be supported without results.
The adverse-event record lists All Participants and reports 0 serious events, 0 other events, and 0 deaths. These are registry entries, not a treatment-arm comparison. The record does not show arm-specific safety counts, event definitions, or how adverse events were collected. The entries should not be taken as proof that no adverse events occurred in either treatment group.
In general, a randomized comparison can support an estimate of the effect of assignment when outcome data and an appropriate analysis are available. Here, those outcome data are absent. The registry record supports description of the design, intervention strategies, endpoint plan, and recorded adverse-event figures, but it does not support a conclusion about the size, direction, or statistical uncertainty of the DVT treatment effect.
9. Statistical Methods Explained
The registry identifies this as a randomized, parallel-group trial with no masking. The following concepts explain how those design features relate to interpretation; they do not imply that an unreported procedure was used.
What does randomization contribute?
Randomization assigns participants to treatment strategies by chance. In general, this helps prevent systematic differences in baseline characteristics from determining who receives each strategy. It supports a fair comparison of outcomes between assigned groups, provided that outcome information is collected and analyzed appropriately. Randomization does not ensure identical groups, and the registry does not describe sequence generation, allocation concealment, or the assignment ratio. Because the outcome data are unavailable, the benefits of random assignment cannot be translated into an estimated treatment effect for this trial.
What does an unmasked design mean?
The registry lists masking as none. In an unmasked study, knowledge of the assigned strategy can potentially influence participant behavior, clinical decisions, or outcome assessment. That is a general methodological concern, not evidence that bias occurred in this trial. The record does not state whether outcome assessors were masked, nor does it describe steps used to limit the influence of treatment knowledge. DVT diagnosis involved both ultrasound screening and standard-care clinical diagnosis, making ascertainment procedures especially important to document.
How was the primary endpoint to be ascertained?
The primary endpoint was development of DVT, with follow-up from the start of intervention to 6 months. The description specifies ultrasound screening on study days 0 and 5 for the first 70 patients. After day 5, and for all remaining subjects, diagnosis was to be according to standard of care by the attending physician. New diagnoses were to be recorded daily until discharge or a maximum of 28 days, with DVT diagnosis also collected at 6 months through the primary care physician’s office or the patient’s household.
In general, consistent outcome definitions and ascertainment help make treatment groups comparable. Scheduled imaging may detect events that would not be diagnosed during ordinary care, while clinical diagnosis depends on the care process. A change in ascertainment over the course of enrollment could therefore affect event detection. The registry does not report whether screening and follow-up were completed as planned, how diagnoses were verified, or how the transition between approaches was handled in analysis.
What statistical analysis is reported?
The registry lists 0 analyses and does not provide an outcome effect estimate or inferential statistics. The statistical analysis plan, including the chosen model, adjustment variables, handling of repeated observations, and approach to censoring or incomplete follow-up, is not reported in the registry record. Without these details and the underlying outcome results, it is not possible to assess whether an analysis matched the study design or endpoint.
In general, the choice of analysis depends on how the endpoint is defined. A simple event proportion, a time-to-event analysis, or another approach can answer different questions and use follow-up information differently. The registry describes event recording over time but does not state which analysis was planned or performed. It would be inappropriate to infer a particular model from the endpoint description alone.
What do planning calculations mean?
The record describes a planning illustration based on an observed effect, using a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such an illustration is not the trial’s own design justification and is not observed power. In general, planning calculations express the sample size that would be needed under stated assumptions about the effect and analysis. They do not demonstrate that a treatment effect exists, and they do not measure the probability that a study has correctly detected an effect after results are known.
For a time-to-event calculation, the record notes that event totals are used; other planning calculations are expressed as participants per arm. The primary outcome is not reduced to one comparison in the record, and no outcome measure data are available. Thus, there is no reported primary effect estimate on which to base a meaningful planning illustration in this interpretation. The original sample-size justification and its assumptions are not reported in the registry record.
Why does over-dispersion matter in general?
Over-dispersion occurs when variation in data is greater than a statistical model assumes. If a model does not account for that extra variation, its standard errors may be too small and its confidence intervals too narrow. This is a general issue for some count outcomes; it is not a reported feature of this trial. The registry does not identify an analysis model or report data that would allow over-dispersion to be assessed.
Overall, the design information explains what comparison was intended, while the absence of analyses and results prevents evaluation of the observed treatment effect, its precision, or the appropriateness of the statistical methods actually used.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists DVT as the primary outcome and pulmonary embolism and sepsis as secondary outcomes. Considering multiple outcomes can increase the chance of finding an apparently notable result by chance if each is tested separately. In general, investigators may address this with a prespecified hierarchy, adjustment, or a clear distinction between confirmatory and exploratory analyses. The registry record does not report whether any such approach was planned or used.
The primary endpoint description also includes several ascertainment methods and follow-up periods. The record indicates that the primary outcome has several categories or time points and is not reduced to one comparison. It does not report how the different periods or sources of diagnosis were combined, whether they were analyzed separately, or which comparison was intended as primary for inference. Consequently, the registry does not support a single primary effect estimate or an assessment of multiplicity across those measures.
Missing outcome data are a central issue: the registry states that no outcome measure data are available. It attributes this to the principal investigator leaving the university in 2013 and unsuccessful attempts to contact the investigator and study team. That explanation concerns the availability of results in the registry; it does not establish whether individual participant outcomes were missing during trial conduct. Reasons for participant-level missingness, loss to follow-up, and methods for handling missing data are not reported in the registry record.
The record lists 0 analyses and does not identify an intention-to-treat, per-protocol, or other analysis population. It also does not report how participants were assigned in practice, whether treatment changes occurred, or how departures from the planned strategy were handled. As a result, neither the population used for an effect estimate nor the consequences of incomplete follow-up can be evaluated.
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 |
|---|---|---|---|
| All Participants | 0 | 152 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| All Participants | 0 of 152 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| All Participants | 0 of 152 |
The registry’s adverse-event entry is labeled All Participants. It reports 0 serious adverse events, 0 other adverse events, and 0 deaths, with 152 listed as at risk for each category. These are the recorded figures in the registry, not a comparison between the intravenous and subcutaneous strategies.
Because the record does not present arm-specific safety counts, it is not possible to compare event occurrence between treatment groups. The record also does not provide event definitions, reporting procedures, follow-up duration for these figures, or detail about how the at-risk population was determined. The entries should therefore be read narrowly as registry-recorded aggregate counts. They do not establish that no event occurred during the trial, that all events were captured, or that the strategies had equivalent safety.
In general, safety comparisons require consistent definitions, comparable observation periods, and counts by assigned treatment. A zero entry can reflect the recorded data, but without the collection and analysis details it cannot explain whether any events were not reported or how safety differed between strategies. No causal conclusion about adverse events is supported by these aggregate figures.
12. What the Result Does, and Does Not, Mean
The registry record documents a randomized comparison of continuous low-dose intravenous heparin with subcutaneous heparin used as standard of care. It identifies DVT as the primary endpoint and describes planned ascertainment through ultrasound, usual clinical diagnosis, and later follow-up. These details establish the study question and intended measurement approach.
They do not establish which strategy had fewer DVT events, whether any observed difference favored either strategy, or how precisely a difference could be estimated. No primary outcome data, treatment-arm event counts, effect estimates, confidence intervals, or p-values are reported. The registry’s completed status does not fill that evidence gap. The listed secondary outcomes also have no reported results.
In general, absence of a reported treatment effect is not evidence that the strategies had the same effect. It is also not evidence that one strategy was better. Equivalence or non-inferiority would require a defined margin and an analysis designed to assess it; neither is reported in the registry record. Likewise, the design description alone cannot establish the success or failure of prevention.
The aggregate adverse-event entries are similarly limited. They do not provide a comparative safety analysis, and they should not be treated as proof of no adverse events in either treatment group. The registry gives useful information about the trial’s design, endpoint plan, and reasons outcome results are unavailable, but it cannot answer the comparative clinical question from results.
Accordingly, the defensible interpretation is descriptive: the trial planned a randomized comparison and recorded an enrollment of 152, but its outcome findings are not available in the registry record. No treatment-effect conclusion or precision assessment can be made from the available results information.
13. Why This Trial Matters Statistically
This trial matters statistically because its design illustrates the difference between a well-defined comparison and an interpretable result. Random allocation was intended to compare an intravenous strategy with a subcutaneous standard-of-care strategy. The primary endpoint was clinically relevant to the stated prevention question, and the registry specifies how DVT was intended to be detected over follow-up.
Yet statistical inference depends on outcome information, not design details alone. Without event counts and an analysis, there is no estimate to interpret and no way to assess its precision. A randomized design can reduce bias in a comparison, but it cannot recover findings that are unavailable. This distinction is important when reading completed trials: completion status and a detailed endpoint description are not substitutes for posted results.
The ascertainment plan also raises a general measurement issue. Scheduled ultrasound screening was planned for the first 70 patients, while later diagnoses were to follow standard care, with longer-term collection at 6 months. In general, differences in how an endpoint is sought can influence its detection. Evaluating that possibility would require information on implementation and analysis that is not reported in the registry record.
The record also illustrates why safety summaries need treatment-specific context. Aggregate adverse-event counts without arm-level detail cannot support a comparison. Similarly, planning assumptions cannot be interpreted as evidence of observed power or treatment efficacy. The registry describes assumptions for planning calculations, but it does not report trial outcome results or the original sample-size justification.
For clinical researchers and biostatisticians, the key lesson is to separate protocol-level information from results-level evidence. The record supports a clear account of the intended question and design, while the missing outcomes prevent statistical conclusions about the intervention comparison.
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 trial-specific limitation for interpretation is the absence of primary and secondary outcome data. The registry states that no outcome measure data are available and explains that the principal investigator left the university in 2013; attempts to contact the investigator and study team were unsuccessful. This leaves no reported DVT counts, treatment comparison, or estimate of uncertainty.
The endpoint plan used different ascertainment approaches over the course of enrollment. Ultrasound screening was planned for the first 70 patients on study days 0 and 5; after day 5 and for all remaining subjects, diagnosis was to follow standard care. New DVT was to be recorded daily through discharge or a maximum of 28 days, with diagnosis also collected at 6 months. The record does not say whether these procedures were completed as planned, how outcomes were verified, or how the varying sources and periods were analyzed.
The registry identifies the trial as unmasked but does not report whether assessors were masked. It also does not report allocation concealment, the randomization procedure, the assignment ratio, adherence, treatment changes, or analysis populations. The statistical analysis plan and original sample-size justification are not reported in the registry record. These omissions prevent assessment of whether the eventual analysis addressed the design and endpoint as intended.
The adverse-event entry is aggregate and does not distinguish treatment groups. Its event definitions and collection methods are not described. Therefore, it cannot support a comparative safety interpretation. The listed secondary outcomes have no reported results, and no multiplicity approach is described.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Using Intravenous Heparin Versus Standard of Care Subcutaneous Heparin to Prevent Clots After Surgery — NCT01608906.
- Registry record last updated 2021-07-29; status last verified 2021-07.
- Results first posted 2021-07-29.
- 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.
Continue through the Clinical Biostats statistical pathway
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18. Record Summary
The registry identifies NCT01608906 as a completed, randomized, parallel-group study with no masking. Its stated comparison was continuous low-dose intravenous heparin, titrated to a PTT of 40-45, versus subcutaneous heparin 5000 units 3 times/day as standard of care. Recorded enrollment was 152.
The primary outcome was development of DVT, with follow-up from the start of intervention to 6 months. Pulmonary embolism and sepsis were listed as secondary outcomes. The registry describes ultrasound screening for the first 70 patients, followed by standard-care diagnosis after day 5 and for remaining subjects, with daily recording through discharge or a maximum of 28 days and further collection at 6 months.
The registry states that no outcome measure data are available, attributing this to the principal investigator leaving the university in 2013 and unsuccessful contact attempts. It lists 0 analyses. Aggregate adverse-event entries report 0 serious events, 0 other events, and 0 deaths for All Participants. These entries do not provide arm-specific comparisons. The registry record therefore describes the trial and its intended endpoint but does not report evidence of the comparative treatment effect.