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 TEsting for Arterial Disease in Diabetes (TrEAD) Study (NCT04058626), a registered phase not stated study. The primary outcome is Diagnostic Accuracy.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04058626 |
| Phase | Phase not stated |
| Condition | Diabetic Foot, Peripheral Arterial Disease, Diabetic Foot Ulcer |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 305 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Imperial College Healthcare NHS Trust |
| Results posted | Yes |
2. Clinical Question
The TrEAD Study asks how accurately bedside tests identify arterial disease in people with diabetes, using a full lower limb Duplex Ultrasound scan as the reference test. It also describes an interest in whether test results are linked to ulcer healing or amputation, but the registry record lists diagnostic accuracy as the primary outcome and does not report results for those other questions.
Population
Diabetic patients evaluated in the study at 2 hospitals. The record lists diabetic foot conditions and peripheral arterial or vascular disease among the conditions of interest. It does not report detailed eligibility criteria or establish that every participant had a foot ulcer.
Intervention
The bedside tests include the Podiatry Ankle Duplex scan (PAD-scan), Transcutaneous pressure of oxygen (TcPO2), Toe Brachial Pressure Index (TBPI), Duplex Assist and Ankle Brachial Pressure Index (ABPI). The brief summary also describes a focused ultrasound test.
Comparator
The reference test is a full lower limb Duplex Ultrasound scan. Each bedside test is to be compared with its findings; this is a diagnostic reference comparison, not a treatment-control comparison.
Primary question
What is the diagnostic accuracy, reported as a percentage with a 95% confidence interval, of PAD-scan and the other bedside tests compared with the reference scan? The registry record gives the outcome definition but does not report the resulting accuracy percentages or intervals.
3. Trial Design
This is a comparative diagnostic accuracy study, not a randomized treatment trial. The registry record describes diabetic patients at 2 hospitals undergoing bedside tests and a full lower limb Duplex Ultrasound scan, which serves as the reference test. Tests are described as being performed on the same day of presentation, within a timeframe of 1 hour.
The interventions listed are diagnostic tests: TcPO2, TBPI, PAD-scan, Duplex Assist and ABPI. The brief summary also describes a focused ultrasound test and comparisons with commonly used tests. The design is therefore about how test classifications correspond to a reference assessment, rather than whether one treatment improves a clinical outcome. Allocation is not stated, and the listed tests do not form randomized treatment arms or a like-for-like control comparison.
Enrollment is 305, and the study status is COMPLETED. The recorded start date is 2019-03-04 and the primary completion date is 2019-10-18. These dates and the enrollment describe the study record; they do not establish how many participants had usable results for every test. The record reports missing data for ABPI, TBPI and TcPO2, so the available information differs by test.
The registry record identifies one primary outcome measure, diagnostic accuracy, expressed as a percentage with a 95% confidence interval. It does not give the estimates, confidence intervals, test thresholds, or the analysis details used to calculate them. It lists no analyses. Whether tests were interpreted blind to one another or to the reference scan, their order, and the approach to resolving disagreements 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 | Study Participants |
|---|---|
| STARTED | 305 |
| COMPLETED | 305 |
| NOT COMPLETED | 0 |
Analysis population for the primary outcome, as defined in the registry: Missing data were observed in 7 (2.3%) patients for ABPI, 71 (23.3%) patients for TBPI and 16 (5.2%) patients for TcPO2.
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 | Study Participants |
|---|---|---|
| Participants analysed | 305 | |
| Age, Continuous | years | 72 (62 to 79) |
| Sex: Female, Male: Female | Participants | 99 |
| Sex: Female, Male: Male | Participants | 206 |
| Race and Ethnicity Not Collected | Participants | — |
| Active ulceration | Participants | 123 |
| Neuropathy | Participants | 203 |
6. Primary Endpoint
The registry lists the primary outcome as Diagnostic Accuracy, measured over 1 hour; all tests will be performed on the same day of presentation..
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | 95% Confidence Interval |
| Unit | Percent |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is diagnostic accuracy: the proportion of test classifications that agree with the reference assessment, expressed as a percentage. The reference assessment is a full lower limb Duplex Ultrasound scan, and the bedside tests under comparison include PAD-scan and the other listed tests. In general, a reference test gives a common basis for evaluating whether an index test identifies the condition of interest.
The registry record specifies a 95% confidence interval alongside the accuracy percentage. In general, a confidence interval communicates uncertainty around an estimate: a narrower interval indicates greater precision, while a wider interval indicates less precision. The record does not report the actual accuracy percentages or intervals, so their magnitudes and precision cannot be assessed from the registry information.
The stated timeframe is 1 hour, with all tests described as occurring on the same day of presentation. Performing tests close in time can make comparisons less vulnerable to changes in a participant's condition between assessments. That is a general design consideration, not evidence that the tests agree or that any particular test performs well. The registry record does not report the case definition, thresholds, or calculation method for the accuracy outcome.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record establishes the question the study was designed to address: how bedside tests for arterial disease in diabetes compare with a full lower limb Duplex Ultrasound scan. It does not report the diagnostic accuracy results. Although the primary outcome is specified as a percentage with a 95% confidence interval, neither the estimates nor the intervals appear in the record information available for interpretation. Consequently, no conclusion about which test had higher accuracy, how large any difference was, or how precisely accuracy was estimated can be drawn from these details.
The record identifies enrollment of 305 and reports test-specific missing data for ABPI, TBPI and TcPO2. Enrollment is not equivalent to the number with an interpretable result for each test. Missing measurements can change the population contributing to a test's estimate and can affect how comparisons are interpreted. The registry record does not state whether analyses used only complete cases, imputed missing measurements, or applied another method.
The comparison is diagnostic rather than therapeutic. A difference in agreement with the reference scan would describe test performance relative to that reference; it would not by itself demonstrate a difference in ulcer healing, amputation, or another patient outcome. The study summary mentions interest in links between results and healing or amputation, but no results or analysis details for those questions are reported in the registry record.
The registry record does not identify thresholds or define how a positive test result was determined. These details matter because diagnostic accuracy depends on how the test classifies participants and how the reference diagnosis is defined. Nor does the record state whether readers were blinded, how inconclusive findings were handled, or whether all tests were evaluated in the same way.
There is no randomized allocation and no treatment control comparison. The same-day testing description supports a paired diagnostic comparison in principle, because tests are intended to be performed on the same participants. However, the actual analysis method is not reported, and test-specific missingness means the available paired observations may differ. Without posted estimates and analysis details, the registry record documents the planned comparison but does not establish comparative performance or clinical consequences.
9. Statistical Methods Explained
Diagnostic accuracy studies assess how well an index test classifies a condition relative to a reference test. In this study, the registry names a full lower limb Duplex Ultrasound scan as the reference and lists several bedside assessments for comparison. The reference provides a common standard for evaluating whether the bedside test results correspond to the reference findings. This approach estimates agreement with the chosen reference; it does not independently establish that the reference itself is error-free.
What does an accuracy percentage represent?
In general, diagnostic accuracy is the share of classifications that match the reference classification. It combines correct positive and correct negative classifications, so the overall value can depend on how common the target condition is in the population being assessed. Other diagnostic measures, such as sensitivity and specificity, answer more targeted questions about positive and negative classifications. The registry record names diagnostic accuracy as the primary outcome but does not state whether sensitivity, specificity, predictive values, or other measures were also calculated.
Interpretation also depends on the threshold used to label an index test positive or negative, and on the corresponding definition of disease status in the reference test. The registry record does not report these thresholds or definitions. A percentage without them may be difficult to reproduce or compare with findings from another setting. The record also does not describe how equivocal or technically unsuccessful test results were treated.
Why report a confidence interval?
A confidence interval expresses sampling uncertainty around an estimate. In general, an estimate from a study population is not known with perfect precision, and an interval gives a range of values compatible with the data under the statistical method used. The registry specifies a 95% confidence interval for the accuracy outcome, but the resulting intervals are not reported. Without the interval endpoints, the precision of any estimate cannot be judged. A confidence interval is not a guarantee that the true value lies within a particular interval, and it does not address every source of bias, such as imperfect reference classification or missing measurements.
What does same-day testing contribute?
The tests are described as being performed within a timeframe of 1 hour and on the same day of presentation. In general, testing the same participants close together can make within-person comparisons useful: differences are less likely to reflect changes over a long period between assessments. Analyses of paired test results can account for the fact that results from one person are related rather than independent. The statistical method used for the comparisons is not reported in the registry record, so it is not possible to determine whether paired methods were applied.
The reference scan and bedside tests are different diagnostic procedures, not randomly allocated interventions. The comparison therefore concerns correspondence with the reference, rather than a causal contrast between treatment groups. The record states that allocation is not stated and indicates that arms are not a like-for-like control comparison. Treating the test groups as independent arms would not reflect the described diagnostic design.
What can planning calculations tell a reader?
Any sample-size values presented as planning illustrations are not observed outcomes and are not evidence of observed power. The stated illustration assumptions use a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect set as a stated fraction of the observed effect. The record does not report a trial-specific sample-size justification, so the planning illustration should not be read as the original design rationale. For time-to-event outcomes, the stated convention is to give a total number of events; other planning values are participants per arm. No such values should be interpreted as trial results.
The registry record lists one outcome measure and no analyses. The outcome description and study summary explain the intended question, but they do not substitute for a statistical analysis plan or for posted estimates. Details including the handling of missing measurements, the comparison procedure, and any adjustment for multiple testing are not reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The record lists multiple bedside tests against the same reference scan. In general, making several comparisons can increase the chance that at least one result appears noteworthy by chance if each is assessed without accounting for the family of comparisons. A multiplicity plan may define which comparisons are primary and whether adjustment is appropriate. The registry record identifies diagnostic accuracy as the primary outcome, but it does not report a multiplicity adjustment or explain how results across tests were prioritized.
Missing data are explicitly reported for ABPI, TBPI and TcPO2: 7 (2.3%) patients for ABPI, 71 (23.3%) patients for TBPI and 16 (5.2%) patients for TcPO2. These are test-specific missingness figures. The record does not give a corresponding missingness figure for every listed test, nor does it explain why measurements were unavailable. Different amounts of missingness can mean that accuracy estimates are based on different subsets of participants, limiting direct comparisons.
The registry record does not report whether missing data were excluded, imputed, or addressed using another method. It also does not describe an analysis population, such as a prespecified complete-case population, or whether inconclusive test results were counted as errors or omitted. These choices can affect estimated accuracy and its confidence interval.
The record lists no analyses and does not report outcome estimates. It also does not state whether the analysis was prespecified, whether any interim analyses took place, or how the planned comparisons were handled statistically. Those details are not reported in the registry record.
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 |
|---|---|---|---|
| Study Participants | 0 | 305 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Study Participants | 0 of 305 |
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 |
|---|---|
| Study Participants | 0 of 305 |
The registry safety figures list Study Participants as the group at risk, with 305 participants at risk for serious adverse events and 305 at risk for other adverse events. The listed number affected is 0 for serious events and 0 for other events; deaths are listed as 0. No serious adverse event terms are listed.
These figures are counts recorded for the study group. They are not diagnostic accuracy results and do not show whether a bedside test correctly identified arterial disease. They also do not establish that a diagnostic procedure has no risk. A zero recorded count means the registry entry lists no events in that category; it should not be interpreted as proof that an event is impossible or that every possible harm was captured.
The record does not provide descriptions of safety monitoring, event definitions, severity grading beyond the serious and other categories, or follow-up duration for safety reporting. It also does not report a comparative safety analysis across individual diagnostic tests. The figures should therefore be read as the registry's event counts for the study group, not as a complete account of procedural safety or a comparison among tests.
12. What the Result Does, and Does Not, Mean
The study record defines a practical diagnostic question: whether bedside tests identify arterial disease in a way that corresponds to a full lower limb Duplex Ultrasound scan. It documents the intended comparison and the use of same-day testing. These features describe the study's purpose and setting, but they do not reveal how accurate any test was.
The registry record does not report accuracy percentages or their 95% confidence intervals. It therefore cannot support a ranking of PAD-scan, TcPO2, TBPI, Duplex Assist or ABPI, nor can it establish that any test is equivalent, superior, or inferior to another. The absence of posted estimates in this record is not evidence that the tests performed alike or differently.
Even when accuracy estimates are available, they concern agreement with a reference test and need not directly answer whether using a test changes care or patient outcomes. The brief summary mentions possible links between test results and ulcer healing or amputation, but those results are not reported in the registry record. Diagnostic classification and clinical outcomes are distinct questions.
Test-specific missingness is relevant to interpretation. The reported missing data for ABPI, TBPI and TcPO2 mean that usable results were not available for every participant for those tests. The record does not state how missing values were handled or whether their absence could be related to participant characteristics or test performance. The resulting uncertainty cannot be fully assessed without that information and the outcome estimates.
Overall, the registry record establishes what was intended to be measured, the reference test, and some features of study conduct. It does not provide enough result or analysis detail to judge test performance, comparative precision, or implications for healing and amputation.
13. Why This Trial Matters Statistically
Diagnostic test comparisons are statistically different from treatment comparisons. The key question is not whether one randomized group improved more than another, but how closely each bedside test classifies participants relative to a reference assessment. The TrEAD Study record makes that distinction explicit by naming a full lower limb Duplex Ultrasound scan as the reference test.
Evaluating multiple bedside tests in the same diagnostic setting can be useful because the tests address a shared clinical problem. The same-day testing description also raises an important analytical point: measurements from the same participant are related. A sound comparison should reflect that pairing rather than treat every test result as if it came from an unrelated group. The statistical approach used is not reported in the registry record.
Precision and missingness matter alongside the point estimate. The primary outcome is described as a percentage with a 95% confidence interval, while missing data are reported for ABPI, TBPI and TcPO2. Both details are central to understanding what an accuracy result would mean: the interval would communicate statistical precision, and test-specific missingness would help readers assess which observations contributed.
The record also illustrates why a study objective is not the same as a result. It identifies diagnostic accuracy as the primary outcome and mentions interest in healing and amputation, but it does not report estimates or analyses. Without those, conclusions about relative performance or patient outcomes are not justified. The design description remains useful for understanding the intended comparison, while the missing results limit what can be inferred.
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 registry record does not report the diagnostic accuracy estimates or their confidence intervals. It therefore does not permit assessment of the size or precision of test performance, or comparison of the listed tests based on observed results. Although the primary outcome is described, the reported information does not include the calculations or findings needed to interpret it.
Several methodological details are not reported in the registry record: diagnostic thresholds, the definition of a positive reference result, treatment of indeterminate findings, blinding, test order, and the statistical method for comparing paired results. These details can affect estimates and their interpretation. The record also does not explain the reasons for missing measurements or how missingness was handled.
Missing data are reported for ABPI, TBPI and TcPO2, with different figures for each test. This limits certainty that comparisons would be based on equivalent participant sets. The record does not report a detailed analysis population or provide missingness information for every listed test.
The registry entry lists no analyses and does not provide results for the proposed links with ulcer healing or amputation. It does not report a multiplicity strategy for the several bedside tests, or a trial-specific sample-size justification. The stated planning assumptions are illustrations, not evidence of the original design rationale or observed power.
Finally, this is a diagnostic comparison against a named reference scan, not a randomized comparison of interventions. The reference standard itself may not capture every aspect of arterial disease, and agreement with it is not identical to clinical benefit. These limitations concern what can be concluded from the registry information; they do not establish that the study's unreported analyses were conducted in any particular way.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: TEsting for Arterial Disease in Diabetes (TrEAD) Study — NCT04058626.
- Registry record last updated 2021-09-02; status last verified 2021-09.
- Results first posted 2021-09-02.
- 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
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
The registry record identifies the TrEAD Study, NCT04058626, as a completed comparative diagnostic accuracy study sponsored by Imperial College Healthcare NHS Trust. Enrollment is 305. The recorded start date is 2019-03-04, and the primary completion date is 2019-10-18.
The study concerns bedside tests for arterial disease in people with diabetes, compared with a full lower limb Duplex Ultrasound scan. The primary outcome is diagnostic accuracy, reported as a percentage with a 95% confidence interval, with testing described as occurring on the same day of presentation within 1 hour.
The record reports missing measurements for ABPI, TBPI and TcPO2, and lists no analyses. It does not report the primary accuracy estimates or confidence intervals, detailed analysis methods, or findings on ulcer healing and amputation. The available record therefore describes the study question and selected conduct details but does not provide the results needed to evaluate comparative test performance.