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 A Clinical Study of the Performance of a Glucose Blinding Protein-Based Continuous Glucose Monitor (GBP CGM) (NCT01469715), a na phase 2 study. The primary outcome is Absolute Relative Difference (ARD).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01469715 |
| Phase | Phase 2 |
| Condition | Type 1 Diabetes Mellitus |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 16 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University of Virginia |
| Results posted | Yes |
2. Clinical Question
Population
Participants with Type 1 Diabetes Mellitus. The registry lists an enrollment of 16. It describes assessment during low, normal, and high glucose conditions, including meal and insulin challenges.
Intervention
The device under evaluation is the Glucose Binding Protein-Based Continuous Glucose Monitor, abbreviated GBP CGM. The study description says each participant will wear one active GBP-CGM and one inactive GBP-CGM.
Comparator
The study is a single-group study, not a randomized comparison. The record does not describe a separate clinical comparator arm. Sensor readings are paired with YSI plasma glucose readings as a reference for assessing performance; that reference measurement is not a treatment control group.
Primary question
How closely do GBP CGM sensor glucose readings correspond to reference plasma glucose readings, as assessed by Absolute Relative Difference across normal, hyperglycemic, and hypoglycemic ranges? The registry also describes interest in warm-up time, trend accuracy, and sensor lag, but does not report numerical results for those measures.
The study description frames the investigation around device performance during a 24 hour period involving a regular dinner meal, a liquid breakfast meal, insulin dosing intended to induce hypoglycemia to a goal of 55 mg/dL, and a regular lunch meal. It also describes low, normal, and high glucose conditions. These are planned assessment conditions, not reported evidence that a particular level of accuracy was achieved.
The registry says the GBP CGM uses a glucose binding protein-based detection method and describes an expectation that this method could improve recognition of glucose at low levels. That expectation is a rationale for investigation, not an endpoint result. The posted record does not give an estimated accuracy value or a statistical comparison establishing that the device performs differently from another monitor.
3. Trial Design
This is a completed, Phase 2, single-group device study sponsored by the University of Virginia. The registry lists enrollment of 16 and dates of 2011-11 for study start and 2012-07 for primary completion. Allocation is recorded as NA, masking as none, and the model as single group. The study is therefore not a randomized comparison of treatment groups, and the active and inactive sensors described in the arm information should not be read as separate randomized arms.
The intervention is the GBP CGM. The registry describes all participants as wearing one active GBP-CGM and one inactive GBP-CGM. The study purpose is to evaluate warm-up, accuracy, and lag performance. Its brief description places monitoring around meals and an insulin challenge intended to reach a low-glucose goal, with assessment spanning low, normal, and high glucose levels. The registry does not report further procedural details, such as the sequence or timing of all assessment activities beyond the stated challenge description.
The primary outcome is titled Absolute Relative Difference and has a timeframe of 25.5 hours. The description gives glucose ranges for the planned assessment and says the study data include 208 paired sensor-YSI plasma glucose readings for each GBP CGM sensor inserted for 24 hours during hyperglycemic and hypoglycemic challenge conditions. These details characterize the intended measurement data; they do not constitute a reported accuracy estimate.
The registry lists one outcome measure and zero analyses. It does not provide a numerical result for the primary outcome, its variability, or a confidence interval. A protocol, statistical analysis plan, sample-size justification, and details of analysis populations are not reported in the registry record. Consequently, the listed design details support a description of what was intended, but not a reconstruction of the full analysis strategy or a judgment about whether the planned assessment was completed as intended.
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 | GBP-CGM |
|---|---|
| STARTED | 16 |
| COMPLETED | 16 |
| 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 | GBP-CGM |
|---|---|---|
| Participants analysed | 12 | |
| Age, Continuous | years | 42 (SD 4) |
| Sex: Female, Male: Female | Participants | 8 |
| Sex: Female, Male: Male | Participants | 4 |
| Duration of Diabetes | years | 22 (SD 11) |
6. Primary Endpoint
The registry lists the primary outcome as Absolute Relative Difference (ARD), measured over 25.5 hours.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | percentage of error |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is titled Absolute Relative Difference (ARD), expressed as a percentage of error. The registry defines it using the sensor glucose value and the reference glucose value: 100*(G sensor-G reference)/G reference. It specifies assessment when the reference glucose is Normal (70-180 mg/dl), Hyperglycemic (>180 mg/dl), and Hypoglycemic (<70 mg/dl). The reference is described as YSI plasma glucose.
In general, a relative error expresses a measurement difference in relation to the reference value, making the error scale-dependent rather than simply reporting a difference in glucose units. The registry’s displayed formula retains the direction of the difference: readings above the reference produce a positive signed value, and readings below it produce a negative signed value. Although the endpoint title uses the word Absolute, the formula as written does not show absolute-value bars or another step that removes the sign. Whether the analysis took an absolute value is not reported in the registry record, so the calculation should be interpreted according to the stated formula rather than assuming an unlisted transformation.
The glucose-range categories make it possible to assess performance separately under different reference glucose conditions. The record also says paired readings can support static accuracy measures, Point CG-EGA, trend accuracy, warm-up time, and sensor lag. Those are described as possible performance parameters, not additional numerical findings. No ARD estimate, distribution, or range-specific result is reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record gives a measurement framework for assessing the GBP CGM, but it does not report a numerical primary endpoint result. It identifies ARD as the primary outcome, defines the reference glucose ranges, and describes paired sensor and YSI measurements. It does not provide a mean or median ARD, a measure of variability, an interval estimate, or a formal test result. Therefore, the posted record does not establish how close the sensor readings were to reference readings in any glucose range.
The stated rationale is that the device uses a different glucose-detection method from commercially available models and is expected by the investigators to recognize glucose rather than other substances. This is an expectation in the study description, not a demonstrated finding. Without reported outcome values, it cannot be assessed from the registry record whether the device met an accuracy target, how performance varied across glucose ranges, or whether low-glucose performance differed from performance at normal or high glucose levels.
The record describes 208 paired sensor-YSI plasma glucose readings for each GBP CGM sensor inserted for 24 hours during hyperglycemic and hypoglycemic challenge conditions. A count of paired observations describes the data structure, but does not by itself show the size or precision of an accuracy estimate. Repeated readings from the same participant or sensor may be related rather than statistically independent. The registry does not report how that dependence was handled, whether observations were excluded, or the number of analyzable paired readings used for any particular estimate.
The single-group design also limits what can be inferred about comparative performance. The record does not describe random assignment to a separate device or control group. The YSI measurements function as a reference for evaluating sensor readings, not as a randomized comparator. Thus, even a reported sensor-reference agreement result would address measurement performance against that reference, not comparative clinical benefit or outcomes.
The safety information lists 0 serious adverse events among 16 participants at risk and 4 participants with other adverse events among 16 at risk. These counts provide limited safety context, but they do not fill the gap in the unreported accuracy results. The record does not list serious adverse event terms, and deaths are not reported in the registry record. Overall, the posted information documents the study question, design, outcome definition, and selected safety counts; it does not provide enough outcome data to quantify device accuracy or its precision.
9. Statistical Methods Explained
The primary measure is a relative sensor error against a reference glucose reading. In general, relative error expresses the size and direction of a measurement discrepancy in relation to the reference value. It can help describe measurement performance over a range of reference values, while an error stated only in glucose units does not itself express the discrepancy relative to the reference. The registry labels the endpoint Absolute Relative Difference and supplies the formula 100*(G sensor-G reference)/G reference. As written, that formula is signed. The record does not explain whether an absolute-value operation was applied in the actual analysis.
What does the reference comparison represent?
The registry identifies YSI plasma glucose as the reference paired with each sensor reading. In general, a reference comparison evaluates agreement between a device measurement and a designated comparator measurement. It does not establish that the reference has no measurement error, and it does not make the study a randomized comparison of devices. The record does not report additional details about reference measurement procedures, calibration, or quality control.
The endpoint is categorized by reference glucose: Normal (70-180 mg/dl), Hyperglycemic (>180 mg/dl), and Hypoglycemic (<70 mg/dl). These categories are defined by the reference measurement, not by the sensor result. The study description separately mentions an insulin challenge with a goal of 55 mg/dL, as well as meal conditions. That goal describes the planned challenge; it is not a reported observed glucose value or an outcome estimate.
Why report more than one accuracy summary?
In general, a mean summarizes the arithmetic average and can be influenced by unusually large errors, while a median describes the central ordered observation and is less influenced by extreme values. Absolute deviations describe error magnitude without direction, whereas signed differences retain whether the sensor reading is higher or lower than the reference. The registry mentions median and mean absolute deviations and median and mean absolute relative deviation among possible static accuracy metrics. It does not report those calculated values. The distinction between signed and absolute quantities matters because a signed average can be small when positive and negative errors offset, even when individual errors are not small.
The record also mentions Point CG-EGA, Rate CG-EGA, warm-up time, and sensor lag. In general, static accuracy summaries concern agreement at measurement points, while trend measures assess changes or rates over time. Warm-up time concerns the interval before a sensor produces usable readings, and lag concerns delay between a changing reference and the sensor response. These concepts describe different aspects of performance and cannot be substituted for one another. Numerical results for these measures are not reported in the registry record.
How should repeated readings be understood?
The registry describes 208 paired sensor-YSI plasma glucose readings for each GBP CGM sensor inserted for 24 hours during hyperglycemic and hypoglycemic challenge conditions. In general, multiple measurements from one participant or sensor may be correlated because they share conditions and a measurement device. Treating correlated readings as if they were independent can make uncertainty appear smaller than it is. Methods that account for clustering or repeated measurements can address this dependence, but the analysis approach is not reported in the registry record. The number of paired readings alone does not reveal the number of independent participants contributing to a particular estimate.
What would an interval estimate add?
In general, a confidence interval describes uncertainty around an estimated quantity under the assumptions of the analysis. A narrow interval indicates greater precision under those assumptions, while a wide interval indicates less precision. The registry does not report a confidence interval for ARD, so the precision of any accuracy estimate cannot be evaluated from the posted record. No interval should be inferred from the paired-reading count alone.
The registry’s sample-size-planning description concerns a planning illustration based on an observed effect, with two-sided significance level 0.05, equal allocation between two arms, a normal approximation, and the effect to detect expressed as a fraction of the observed effect. It distinguishes planning illustrations for participants per arm from total event counts for time-to-event settings. Those are generic illustration assumptions, not evidence of the original study’s design justification. This study is recorded as single group, not a two-arm randomized comparison, and no observed effect is reported. The protocol’s sample-size justification is not reported in the registry record. Planning illustrations must not be interpreted as observed power or as evidence that the study had adequate precision.
More broadly, a statistical test and an estimate answer different questions. A test evaluates compatibility with a specified null hypothesis under a statistical model, while an estimate describes the magnitude of the measured quantity. Neither can be reconstructed because the registry does not report an endpoint estimate, a test, or the statistical model used. General statistical concepts explain how such outputs might be interpreted, but they cannot replace the missing analysis details.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists one outcome measure and zero analyses. It does not report numerical primary endpoint findings or results for the additional performance parameters mentioned in the outcome description. A statistical analysis plan, a hierarchy of outcomes, and any multiplicity adjustment are not reported in the registry record.
In general, multiplicity arises when several outcomes, subgroups, time points, or statistical tests are examined. Repeated testing can increase the chance of a finding that appears notable by chance; prespecified testing strategies can address that issue. The record does not establish how many analyses were planned or performed, so it is not possible to assess multiplicity handling or determine whether the listed glucose categories were treated as separate confirmatory analyses.
Missing-data rules and the handling of incomplete sensor-reference pairs are not reported in the registry record. In general, missing measurements can affect both the estimate and its precision, particularly if the reasons for missingness are related to device performance or participant conditions. The record does not state how many participants or paired readings contributed to each outcome analysis, whether any readings were excluded, or how missing observations were handled.
The analysis populations are also not reported in the registry record. The enrollment of 16 does not establish that all enrolled participants contributed to every endpoint analysis. No intention-to-treat, per-protocol, or evaluable-device population is specified. These omissions limit assessment of the analysis denominator, potential selection effects, and the relationship between enrollment and the data used to calculate performance.
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 |
|---|---|---|---|
| GBP-CGM | 0 | 16 | 0.0% |
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 |
|---|---|
| GBP-CGM | 4 of 16 |
Most frequent non-serious adverse event terms
| Event term | Organ system | GBP-CGM |
|---|---|---|
| Erythema (score=2) | Skin and subcutaneous tissue disorders | 4 of 16 |
The adverse-event information lists 0 serious adverse events among 16 participants at risk. It lists 4 participants with other adverse events among 16 at risk. These are the registry’s reported counts; they should be read as separate serious and other adverse-event categories, not as evidence about the nature, timing, or cause of individual events.
The serious adverse event terms are not listed. The death count is not reported in the registry record. The record does not provide event descriptions, severity details for the other adverse events, exposure time by participant, or an assessment of whether events were related to the device or study procedures. Consequently, these counts offer only a limited summary of the posted safety information.
In general, the absence of reported serious events in a small study does not establish that a device has no serious risks. Safety counts also cannot be directly compared across studies without considering differences in participants, follow-up, exposure, and event definitions. The registry’s safety entries do not answer the separate question of sensor accuracy, for which numerical results are not reported.
12. What the Result Does, and Does Not, Mean
This study addresses a measurement question: how the GBP CGM’s sensor readings correspond to YSI plasma glucose readings across specified glucose ranges and challenge conditions. The registry describes the device, single-group design, paired measurement approach, and planned performance measures. These registry entries establish the intended evaluation framework, but the posted results do not include a numerical ARD estimate or another reported accuracy analysis.
Accordingly, the record does not show how accurate the device was, how much its readings varied, whether its performance differed across glucose ranges, or how precisely any estimate was measured. It also does not report numerical findings for warm-up time, trend accuracy, or sensor lag. The study description’s expectation that the detection method could improve recognition of glucose at low levels is a hypothesis or rationale, not a result.
The data description includes 208 paired sensor-YSI plasma glucose readings for each GBP CGM sensor inserted for 24 hours during hyperglycemic and hypoglycemic challenge conditions. That describes the planned or available measurement structure, not the performance result. In general, paired observations need to be analyzed in a way that accounts for their context and any repeated measurements. The analysis method is not reported in the registry record.
The design is single group and not randomized. YSI is the reference for evaluating sensor readings, not a clinical comparator group. The record therefore does not support a randomized comparative claim, and it does not report clinical outcomes that would establish a treatment effect. No conclusion about medical use or patient benefit follows from the endpoint definition or the investigators’ expectation alone.
The registry reports 0 serious adverse events among 16 participants at risk and 4 participants with other adverse events among 16 at risk, with limited additional detail. These safety entries should not be treated as a complete account of possible harms. Taken together, the record supports a description of what the study set out to measure and a narrow reading of the posted safety counts; it does not quantify device accuracy or resolve comparative performance.
13. Why This Trial Matters Statistically
This study is statistically relevant because continuous glucose monitoring generates repeated measurements across changing conditions, while device accuracy is commonly assessed against a reference measurement. The registry’s design description makes clear that the performance question involves both the size and direction of sensor-reference discrepancies and the glucose range in which they occur. Such distinctions matter: an overall summary can conceal different performance patterns at low, normal, and high reference glucose levels.
The study also illustrates why an endpoint definition is not the same as an endpoint result. The record names ARD, gives a formula and range categories, and describes paired observations. Yet no numerical accuracy estimate, uncertainty interval, or analysis is reported. Without those results, readers cannot judge either the magnitude of measurement error or the precision of the estimated performance. A substantial count of repeated readings does not alone establish precision, because observations may be clustered within participants and sensors.
The endpoint label and formula also require careful reading. The label includes Absolute, whereas the displayed expression is signed. That difference affects interpretation: a signed quantity retains whether a sensor reading is high or low relative to the reference, while an absolute quantity represents magnitude without direction. The registry does not clarify which form was analyzed.
Finally, the single-group design separates measurement validation from comparative clinical evaluation. The reference readings can anchor an accuracy assessment, but they do not create randomized device groups. The registry’s stated expectation about low-glucose performance should therefore remain distinct from evidence. The study record is useful for identifying the measurement question and its methodological requirements, while its missing results sharply limit statistical conclusions.
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 in the registry record is the absence of numerical primary endpoint results. No ARD estimate, variability measure, confidence interval, or statistical test is reported. The additional accuracy and dynamic performance measures named in the description also lack posted numerical findings. As a result, the record cannot establish the magnitude or precision of sensor performance.
The displayed ARD formula is signed even though the endpoint title says Absolute Relative Difference. The registry does not explain whether an absolute value was used in the analysis. It also does not report whether results were summarized by participant, sensor, glucose category, or individual paired reading. This leaves uncertainty about the precise estimand and summary method.
The record describes 208 paired readings for each sensor and 24-hour sensor insertion, while the primary outcome timeframe is listed as 25.5 hours. It does not explain the relationship between those time descriptions or the analysis window used for each reported endpoint. Details of sensor handling, calibration, exclusions, reference measurement procedures, and repeated-measure modeling are not reported in the registry record.
Enrollment was 16, and the study is a single-group, nonrandomized evaluation with no masking. There is no separate randomized clinical comparator group. The record does not report the number of participants or readings included in each analysis, missing-data procedures, protocol deviations, or analysis populations. A sample-size justification and statistical analysis plan are not reported in the registry record.
The safety entries are limited to counts, without event terms for serious events or further details on the other adverse events. Deaths are not reported in the registry record. These design and reporting limitations constrain interpretation, but they should not be mistaken for evidence that a particular result was favorable or unfavorable.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: A Clinical Study of the Performance of a Glucose Blinding Protein-Based Continuous Glucose Monitor (GBP CGM) — NCT01469715.
- Registry record last updated 2015-07-31; status last verified 2015-07.
- Results first posted 2015-07-31.
- 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 a completed Phase 2, single-group study sponsored by the University of Virginia, with enrollment of 16 participants with Type 1 Diabetes Mellitus. Study start is listed as 2011-11 and primary completion as 2012-07. Allocation is NA, masking is none, and the intervention is the GBP CGM.
The primary outcome is Absolute Relative Difference, assessed against YSI plasma glucose across normal, hyperglycemic, and hypoglycemic reference ranges. The record describes meal and insulin challenge conditions and paired sensor-reference readings. It lists one outcome measure and zero analyses, and does not report a numerical accuracy result or its precision.
Safety entries list 0 serious adverse events among 16 participants at risk and 4 participants with other adverse events among 16 at risk. Serious event terms and deaths are not reported in the registry record. The record supports describing the study question and design, but not drawing a numerical conclusion about device accuracy.