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 Evaluation of Anti-Xa Levels in Surgery Patients Receiving Fixed Dose Heparin (NCT02970032), a non-randomized early/phase 1 study. The primary outcome is Number of Participants With Anti-Xa Levels Within Target Range (0.1-0.35 IU/mL).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02970032 |
| Phase | EARLY/Phase 1 |
| Condition | Deep-Venous Thrombosis, Pulmonary Embolism, Venous Thromboembolism |
| Allocation | Non-Randomized |
| Design model | Crossover |
| Masking | None (open label) |
| Enrollment | 20 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University of Utah |
| Results posted | Yes |
2. Clinical Question
Population
Surgical patients undergoing microvascular surgery who are receiving a heparin infusion for venous thromboembolism prophylaxis. The registry summary says patients were identified while on heparin; the attending surgeon, rather than the study, determined whether to initiate the infusion.
Intervention
For patients whose anti-Xa levels were outside the target range, the study used pharmacist-driven, real-time heparin dose adjustment under a pilot protocol, with follow-up steady-state anti-Xa monitoring.
Comparator
The initial observational approach was a fixed heparin infusion of 500 units/hour, with anti-Xa monitoring. The record does not describe a randomized, concurrent control group; patients with out-of-range levels could cross over to dose adjustment.
Primary question
Among patients receiving a fixed infusion of 500 units/hour, how many had anti-Xa levels in the target range of 0.1 to 0.35 IU/mL? The registry summary also frames the question as the percentage of patients in range. The recorded primary endpoint is a participant count, but the registry record does not report its result.
The study addresses whether monitoring identifies patients whose anti-Xa levels are outside the intended range while receiving fixed-dose heparin, and whether a pilot dose-adjustment approach can guide subsequent infusion changes. Anti-Xa levels are used to monitor anticoagulant therapy, according to the endpoint description. The clinical context is prevention of venous thromboembolism in patients undergoing microvascular surgery, with deep-venous thrombosis, pulmonary embolism, and venous thromboembolism listed as conditions.
The study is not structured as a randomized comparison of fixed dosing against dose adjustment. All patients were to begin in the observational arm, and only patients with out-of-range levels were eligible to cross over to the interventional approach. This pathway means the groups represent different stages of management and patient circumstances, not interchangeable treatment assignments. The registry record does not report the primary outcome count, the number of patients who crossed over, or the subsequent anti-Xa results. Consequently, it does not permit a quantitative answer to the clinical question from the results recorded there.
3. Trial Design
This completed, early-phase study was registered as a non-randomized crossover trial with no masking. Enrollment was 20. The study involved an observational approach using a fixed-dose heparin infusion and anti-Xa monitoring, followed by a possible crossover to real-time dose adjustment for patients whose anti-Xa levels were out of range. The registry record describes the intervention as a pilot protocol, rather than as a randomized assignment between competing strategies.
The brief summary states that the proposed research did not dictate initiation of the heparin drip intraoperatively. Patients were identified after they had been placed on a fixed-dose infusion at their attending surgeon’s discretion. Those whose levels were outside the target range were to receive pharmacist-driven dose adjustments and follow-up steady-state anti-Xa measurements. Monitoring was to stop under conditions described in the arm description, including obtaining in-range peak levels or discontinuation of the infusion around surgery; the available description is truncated, so further details are not reported in the registry record.
The primary outcome was the number of participants with anti-Xa levels within the target range of 0.1–0.35 IU/mL while on an infusion of 500 units/hour. The summary describes this outcome as a percentage, while the endpoint entry specifies a participant count. The registry record gives a timeframe of through study completion, an average of 1 year. A secondary outcome is the number of rate adjustments, but its result is not reported in the registry record.
The study started on 2016-11-10, had a primary completion date of 2017-09-10, and is marked completed. The sponsor is the University of Utah. Because treatment allocation was non-randomized and crossover was triggered by out-of-range levels, comparisons between the two treatment stages are not like-for-like comparisons. The registry record does not report a detailed statistical analysis plan, a sample-size justification, or the number of participants who completed each stage.
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: All 20 patients that were enrolled in the standard heparin dose arm crossed over into the real time heparin dose adjustment arm per the pilot protocol with undetectable anti-Xa levels (\<0.10).
Standard Heparin Dose
| Stage | Standard Heparin Dose Followed by Dose Adjustment |
|---|---|
| STARTED | 20 |
| COMPLETED | 20 |
| NOT COMPLETED | 0 |
Real Time Heparin Dose Adjustment
| Stage | Standard Heparin Dose Followed by Dose Adjustment |
|---|---|
| STARTED | 20 |
| COMPLETED | 20 |
| NOT COMPLETED | 0 |
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 | Standard Heparin Dose Followed by Dose Adjustment |
|---|---|---|
| Participants analysed | 20 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 20 |
| Age, Categorical: >=65 years | Participants | 0 |
| Sex: Female, Male: Female | Participants | 13 |
| Sex: Female, Male: Male | Participants | 7 |
| Race and Ethnicity Not Collected | Participants | — |
| Weight | Kilograms | 20 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Participants With Anti-Xa Levels Within Target Range (0.1-0.35 IU/mL), measured over Through study completion, an average of 1 year..
| Element | Registry entry |
|---|---|
| Result type | Count Of Participants |
| Measure of spread | not applicable |
| Unit | Participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint concerns the number of participants whose anti-Xa levels fell within the target range of 0.1–0.35 IU/mL while receiving a fixed heparin infusion at 500 units/hour. The registry summary describes the intended outcome as the percentage of patients in range, whereas the primary outcome entry is recorded as a count of participants. Neither form of the primary result is reported in the registry record.
Anti-Xa levels are used to monitor anticoagulant therapy, as stated in the endpoint description. The target-range measure therefore assesses whether measured levels meet the study’s specified laboratory range during fixed-dose infusion. It is a monitoring endpoint: it records a laboratory category, not a clinical event such as deep-venous thrombosis or pulmonary embolism. The registry’s listed conditions do not establish that these conditions occurred as study outcomes.
For interpretation, the denominator and assessment rules matter. A participant count needs a clearly defined group of eligible or assessed participants; a percentage additionally requires a denominator. The endpoint entry does not report either a result or the denominator used for a percentage. The registry record also does not specify the precise sampling schedule, how repeated measurements were handled in determining participant status, or whether a participant needed a particular number of in-range measurements to count as within range. Without those details and the outcome result, the endpoint’s observed frequency and precision cannot be assessed.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies the intended primary measure and target range, but it does not report the observed primary outcome. There is no posted count of participants with anti-Xa levels in range, no reported percentage, and no stated denominator for such a percentage. As a result, the record does not establish how often the target range was reached during fixed-dose infusion or how precisely that frequency was estimated.
The design also limits interpretation of any comparison between fixed dosing and real-time dose adjustment. All patients were initially in the observational approach, and only those with out-of-range levels were to cross over. This means the intervention group was selected based on a measurement that was already outside the desired range. Patients who received dose adjustment therefore cannot be treated as a comparable control group for those who remained on the fixed infusion. Differences between stages could reflect the selection pathway, changes over time, monitoring, or dose adjustment, and the registry record does not report an analysis that separates these possibilities.
For a crossover study, repeated observations from the same participant are related. General statistical interpretation should account for that dependence when multiple measurements or treatment stages contribute data. The record does not describe how repeated anti-Xa measurements were reduced to the participant-level endpoint or how within-person dependence was handled. No model, test, confidence interval, or p-value is recorded among the analyses.
The registry lists enrollment of 20, but enrollment alone does not tell readers how many participants had evaluable primary endpoint data, how many had out-of-range levels, or how many received dose adjustments. Those figures are not reported in the registry record. The sample-size assumptions describe a planning illustration based on an observed effect, equal allocation, a normal approximation, and a two-sided significance level of 0.05. Such planning calculations are not observed power and do not substitute for a reported outcome or its uncertainty. The actual sample-size justification is not reported in the registry record.
The safety entries list serious adverse events for both named groups, including a count of 1 in each, with no deaths recorded in either group. These entries should not be interpreted as a direct safety comparison: the study was non-randomized, the intervention was available after out-of-range levels, and the registry does not clarify whether group entries refer to distinct participants or overlapping treatment stages. The serious-event term pulmonary embolism is listed at 5.0%, but the registry record does not define the context or denominator for that percentage.
Overall, the posted information describes a monitoring and dose-adjustment pathway, not a causal estimate of the benefit or harm of dose adjustment. The primary outcome and rate-adjustment results are absent. Any conclusion about the frequency of in-range anti-Xa levels, treatment effects, or comparative safety would go beyond the results reported in the registry.
9. Statistical Methods Explained
Statistical interpretation depends on what was measured, how participants entered each treatment stage, and how the results were summarized. In this study, the primary endpoint is a participant count for anti-Xa levels within the specified target range during infusion at 500 units/hour. The registry summary also describes the intended measure as a percentage. A count reports the number meeting a criterion; a percentage expresses that count relative to a defined denominator. The denominator and observed result are not reported in the registry record, so neither a rate nor its precision can be interpreted.
Why does the crossover pathway matter?
In a randomized comparison, assignment to treatment is intended to make groups comparable, on average, with respect to measured and unmeasured factors. This study was non-randomized. Patients were first observed while receiving fixed-dose heparin, and patients with out-of-range anti-Xa levels could then receive real-time adjustment. Eligibility for the adjustment stage therefore depended on a preceding measurement. Comparing outcomes across those stages would mix the effect of adjustment with the reasons patients entered the adjustment stage.
Crossover designs can also involve repeated observations from the same participant. Those observations are generally correlated: a participant’s measurements may share characteristics that make them more alike than measurements from different participants. General statistical methods for repeated or paired data account for this dependence; treating each measurement as independent can make uncertainty appear smaller than it is. The registry does not report the measurement-level data, a repeated-measures method, or a participant-level rule for determining whether the primary endpoint was met. It is therefore not possible to assess whether or how these issues were handled.
What does uncertainty mean for this endpoint?
A confidence interval is a statistical range that expresses uncertainty around an estimate under a specified method. For a participant count or percentage, it can help distinguish a relatively precise estimate from one compatible with a broad range of underlying values. No primary estimate or confidence interval is reported in the registry record. The record also does not report a hypothesis test or p-value for the primary endpoint. Without an estimate and an uncertainty measure, readers cannot judge the precision of the observed frequency, even if the study’s enrollment is known.
The outcome is a laboratory target-range status, not a time-to-event outcome. A participant-level summary could be based on a defined measurement or on multiple measurements, but the registry record does not explain which measurements determine status. The stated timeframe is through study completion, an average of 1 year. The precise timing and number of anti-Xa assessments for each participant are not reported in the registry record. This matters because the summary can differ depending on whether it represents a measurement at a specified time, any measurement in range, or a participant’s status after a defined monitoring process.
What role does the planning illustration have?
The sample-size assumptions describe a planning illustration computed from the observed effect, with a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. These are assumptions for a planning calculation, not a description of a randomized trial design or an analysis of the observed data. Sample-size calculations can illustrate how a proposed effect and assumptions relate to a future study’s planning requirements; they do not show that the present study had adequate power or that an effect was detected.
The record does not give the trial’s own sample-size justification or the effect estimate used in the planning illustration. It also does not report the calculated planning values in the information available for interpretation. Therefore no numerical planning requirement can be discussed. A planning illustration is not observed power: observed power is not a substitute for reporting the estimated effect and its uncertainty, and calculations based on an observed effect are particularly dependent on that estimate.
What analyses are documented?
No analysis records are listed. The statistical plan, including any prespecified model, handling of missing observations, adjustment for repeated measurements, or approach to subgroup and secondary-outcome analyses, is not reported in the registry record. The record lists the number of rate adjustments as a secondary outcome but does not report its result. There is also no reported statistical comparison between the observational and dose-adjustment stages.
General methods for count or binary outcomes may include estimates of proportions with confidence intervals, but selecting a method depends on the outcome definition, denominator, and data structure. Here, the registry identifies a count-type primary outcome, yet does not provide the result or the rules needed to reproduce an estimate. Recalculations from posted summary statistics are not possible from the recorded primary endpoint information. No recalculated result should be substituted for an analysis that the sponsor may have conducted but that is not reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists a primary outcome concerning participants whose anti-Xa levels were within the target range and a secondary outcome concerning the number of rate adjustments. It does not report results for either outcome. Although the record identifies two outcome measures, it does not describe a multiplicity strategy, such as prioritizing tests or adjusting interpretation when several outcomes are analyzed. The analysis plan is not reported in the registry record, so it is not possible to determine whether additional outcomes or analyses were prespecified.
Missing data are also not described. The registry does not report how many participants had usable anti-Xa measurements, whether any participants withdrew or had incomplete monitoring, or how missing measurements would affect the participant-level endpoint. It does not say whether the primary endpoint was analyzed among all enrolled participants, only those with an available measurement, or another analysis population. These details are important because the observed count and percentage can depend on who is included and how incomplete records are handled.
The registry’s enrollment figure is not a substitute for an analysis-population description. In a study with crossover triggered by out-of-range levels, the numbers contributing to the initial monitoring stage and subsequent adjustment stage may differ, and participants may contribute data to both. The record does not report those stage-specific counts or clarify how overlap was represented in the analysis. It also does not report a method for accounting for repeated measurements or within-participant dependence.
Consequently, the available record does not support an assessment of selective outcome reporting, missing-data bias, or multiplicity-adjusted inference. Those issues remain unresolved rather than evidence that a particular analysis choice was made.
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 |
|---|---|---|---|
| Standard Heparin Dose | 1 | 20 | 5.0% |
| Real Time Heparin Dose Adjustment | 1 | 20 | 5.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Standard Heparin Dose | 0 of 20 |
| Real Time Heparin Dose Adjustment | 0 of 20 |
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 |
|---|---|
| Standard Heparin Dose | 1 of 20 |
| Real Time Heparin Dose Adjustment | 1 of 20 |
Most frequent serious adverse event terms
| Event term | Organ system | Standard Heparin Dose | Real Time Heparin Dose Adjustment |
|---|---|---|---|
| Pulmonary embolism | Respiratory, thoracic and mediastinal disorders | 1 of 20 | 1 of 20 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Standard Heparin Dose | Real Time Heparin Dose Adjustment |
|---|---|---|---|
| Pulmonary Embolism | Respiratory, thoracic and mediastinal disorders | 1 of 20 | 1 of 20 |
Serious events with the highest arm-level rate: pulmonary embolism (5.0%).
The registry lists serious adverse event entries for the Standard Heparin Dose group and the Real Time Heparin Dose Adjustment group. Each entry records 20 at risk and 1 affected for serious adverse events, and 20 at risk and 1 affected for other adverse events. Deaths are recorded as 0 in each group. Pulmonary embolism appears among the top serious-event terms at 5.0%.
These entries require caution. The design was non-randomized, and patients could enter the dose-adjustment stage after an out-of-range anti-Xa result. The named groups are therefore not established as independent, comparable treatment groups. The registry record does not clarify whether participants could be counted in both entries, what period of observation applies to each group, or what denominator is used for the 5.0% pulmonary embolism figure. The repeated at-risk counts should not be added or interpreted as separate sets of participants.
The adverse-event figures are descriptive registry entries, not evidence of a causal safety difference between strategies. The record does not provide event-level timing, severity details beyond the serious-event classification, attribution to heparin or dose adjustment, or a statistical comparison. The absence of recorded deaths does not establish that the study had enough information to exclude uncommon harms. The pulmonary embolism term also should not be treated as a study efficacy result: it is listed as a serious adverse event, and the registry does not explain its relationship to the study’s conditions or endpoint.
12. What the Result Does, and Does Not, Mean
The record’s main contribution is to describe a clinical monitoring question and a pathway for adjusting heparin infusions when anti-Xa levels are outside a target range. It specifies a fixed infusion rate of 500 units/hour, a target range of 0.1–0.35 IU/mL, and real-time adjustment under a pilot protocol for patients with out-of-range measurements. It also identifies a primary endpoint intended to count participants whose levels were in range.
The record does not report the primary endpoint result, a percentage, or a denominator. It does not report the number of participants who crossed over, the number of dose adjustments, or the follow-up anti-Xa results. It therefore cannot show how often participants reached the target range, how much levels changed after adjustment, or how precise any such estimate would be. The completed status indicates the study’s registry status, not that results are available in the record.
The non-randomized crossover design also does not support a simple causal comparison between the fixed-dose and dose-adjustment stages. Participants entered the latter stage because their levels were out of range, so the stages differ by design. Any apparent change after adjustment could be affected by that selection and by the timing and repetition of measurements. The statistical analysis needed to address those features is not reported in the registry record.
These limitations do not show that the protocol failed, nor do they establish that it achieved its target. They define what can be concluded from the recorded information: the study was designed to monitor anti-Xa levels and adjust infusions for out-of-range results, but the posted record does not supply outcome findings that quantify performance or comparative effects. Clinical decisions should not be based on this incomplete registry information alone.
13. Why This Trial Matters Statistically
This study is statistically informative as an example of how a clinical monitoring pathway can complicate comparisons. The fixed-dose stage was observational, while the dose-adjustment stage was reserved for patients with out-of-range anti-Xa levels. That rule is clinically meaningful but also makes treatment-stage groups systematically different. A direct comparison between them would not have the protection against selection bias that random allocation is designed to provide.
The endpoint illustrates the difference between a clearly stated measurement target and a fully interpretable result. The record names the target range and the infusion rate, but does not give the participant count, denominator, or percentage that would answer the primary question. It also does not explain how repeated measurements were translated into participant status. Statistical interpretation requires both a well-defined estimand—the quantity the study intends to estimate—and results reported in a form that allows its uncertainty to be judged.
The crossover pathway raises a further analytic issue: repeated anti-Xa measurements from the same patient are not necessarily independent. Methods should reflect the participant-level structure when repeated measurements contribute to an estimate. The registry record does not describe such a method. Its planning assumptions are not an analysis of the observed data and do not remedy the absence of an effect estimate or uncertainty interval.
Finally, the safety entries demonstrate why descriptive counts need design context. Identical at-risk entries across groups do not establish independent groups, and a serious-event listing cannot by itself establish a treatment-related difference. Transparent reporting of outcome definitions, participant flow, missing measurements, analysis populations, and uncertainty would be needed for a more complete statistical assessment. The record identifies the question, but leaves these key interpretive elements unreported.
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 primary limitation is that the registry record does not report the primary outcome result. Although it defines the target range and states that the endpoint is a participant count, it does not provide the count, a percentage, or the denominator. The secondary outcome, number of rate adjustments, is also listed without a result. Consequently, the record does not permit estimation of the frequency of in-range levels or the amount of adjustment required.
The study’s non-randomized, crossover pathway restricts comparisons. Patients receiving real-time adjustment were selected because their earlier anti-Xa levels were out of range. This makes the observational and intervention stages unsuitable as straightforward control and treatment groups. The record does not report an analytic strategy addressing this selection or the likely dependence of repeated measurements within a participant.
Important operational details are absent or incomplete. The available arm descriptions are truncated, and the registry does not specify the sampling schedule, the rule for classifying a participant as in range, the number of measurements per participant, or how measurements taken at different stages were used. It does not report participant flow, stage-specific enrollment, missing observations, or the analysis population. These omissions limit reproducibility and make it difficult to judge how representative the endpoint would be of the monitoring process.
The registry record also does not report a statistical analysis plan, sample-size justification, inferential analysis, confidence intervals, or p-values. The planning assumptions do not establish study power or replace estimates with uncertainty. Safety entries are descriptive and lack sufficient context for comparative interpretation, particularly given possible overlap between stages. These limitations concern what is documented in the registry record; they do not establish what analyses may have been conducted outside it.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Evaluation of Anti-Xa Levels in Surgery Patients Receiving Fixed Dose Heparin — NCT02970032.
- Registry record last updated 2019-07-24; status last verified 2019-07.
- Results first posted 2019-06-24.
- 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
NCT02970032, titled “Evaluation of Anti-Xa Levels in Surgery Patients Receiving Fixed Dose Heparin,” is a completed, early-phase, non-randomized crossover study sponsored by the University of Utah. Enrollment was 20. The study began on 2016-11-10, with primary completion on 2017-09-10.
Patients undergoing microvascular surgery were monitored while receiving fixed-dose heparin at 500 units/hour. The primary question concerned the number of participants with anti-Xa levels in the target range of 0.1–0.35 IU/mL. Patients with out-of-range levels could receive pharmacist-driven real-time dose adjustment under a pilot protocol. The record lists the number of rate adjustments as a secondary outcome.
The registry record does not report the primary outcome result, the secondary outcome result, or a statistical analysis. Its safety entries list serious and other adverse events for both named groups, but the non-randomized crossover design and lack of denominator context preclude a simple comparative reading. The posted information describes the study pathway but does not quantify its outcome findings.