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 Serum Concentration of Lidocaine After Local Injection During Mohs Micrographic Surgery (NCT00793169), a registered phase not stated study. The primary outcome is The Number of Subjects With Detectable Serum Lidocaine Concentrations (<0.1 ug/mL) at Each Blood Draw..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00793169 |
| Phase | Phase not stated |
| Condition | Basal Cell Carcinoma, Squamous Cell Carcinoma |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 19 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Northwestern University |
| Results posted | Yes |
2. Clinical Question
The study asks whether lidocaine injected locally during Mohs micrographic surgery is followed by measurable serum lidocaine concentrations, and whether high serum concentrations are sustained after intralesional anesthesia on the face or neck. The registry record frames the concern in relation to concentrations that could cause systemic symptoms, but it does not report a concentration associated with symptoms or give symptom results.
Population
Participants with basal cell carcinoma or squamous cell carcinoma of the face or neck who required Mohs micrographic surgery. The registry lists enrollment as 19. The study description also refers to 10 subjects, so the intended number in that description differs from the recorded enrollment; the reason is not reported in the registry record.
Intervention
Local lidocaine injection was used during the surgical procedure. The listed study procedure is blood drawing, with samples collected before, during, and after Mohs micrographic surgery. A brief questionnaire is also mentioned in the study description.
Comparator
No randomized comparator is described. The registry identifies the study as non-randomized and says allocation was not stated. The blood draws at different points in the procedure are repeated observations, not separate treatment arms or a like-for-like control comparison.
Primary question
How many participants had detectable serum lidocaine concentrations at each blood draw during the stated 6 hours? The endpoint title specifies concentrations as <0.1 ug/mL. The registry record does not provide the count at each draw or clarify the assay interpretation of that threshold.
3. Trial Design
This was a completed cross-sectional study, sponsored by Northwestern University. The registry lists a start of 2007-09 and primary completion of 2008-07. The study description focuses on people with basal cell carcinoma or squamous cell carcinoma of the face or neck who were undergoing Mohs micrographic surgery. Enrollment is recorded as 19, while the summary describes a study of 10 subjects; the reason for the difference is not reported in the registry record.
The study followed participants through their procedure rather than assigning them to randomized treatment groups. Its listed procedure was blood drawing, and the arm description says blood was collected before, during, and after surgery. The summary also mentions a brief questionnaire. Exact blood-draw times, the number of draws per participant, the lidocaine dose and injection schedule, and any variation in the surgical procedures are not reported in the registry record.
The primary endpoint is described as the number of subjects with detectable serum lidocaine concentrations (<0.1 ug/mL) at each blood draw, with a timeframe of 6 hours. The population note says the analysis was per protocol. The record lists one outcome measure and no analyses. It does not provide a participant flow account, the number with samples available at each draw, or details of exclusions from the per-protocol population.
Because the design does not identify a randomized control group, observations across blood-draw times should be read as measurements within the surgical setting, not as a treatment-versus-control effect. The registry does not report a protocol, a statistical analysis plan, or whether measurement times and analytic choices were prespecified.
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 | Detectable Lidocaine Concentrations at Each Blood Draw |
|---|---|
| STARTED | 19 |
| COMPLETED | 19 |
| NOT COMPLETED | 0 |
Analysis population for the primary outcome, as defined in the registry: Analysis was per protocol.
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 | Detectable Lidocaine Concentrations at Each Blood Draw |
|---|---|---|
| Participants analysed | 19 | |
| Age, Continuous | years | 60 (42 to 96) |
| Sex: Female, Male: Female | Participants | 7 |
| Sex: Female, Male: Male | Participants | 12 |
| Region of Enrollment: United States | participants | 19 |
6. Primary Endpoint
The registry lists the primary outcome as The Number of Subjects With Detectable Serum Lidocaine Concentrations (<0.1 ug/mL) at Each Blood Draw., measured over 6 hours.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | Participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint counts participants meeting the registry’s stated definition of detectable serum lidocaine concentrations at each blood draw. The endpoint title includes the threshold <0.1 ug/mL, and the timeframe is 6 hours. Since measurements were taken before, during, and after Mohs micrographic surgery, this outcome is intended to describe the pattern of detectability across the procedure and its observation period. It is a count of participants, not a mean concentration or a continuous measure of change.
Repeated blood measurements can describe whether serum lidocaine was detected at different collection points. They may therefore address the study’s stated interest in concentration after local injection and whether high levels are sustained. However, the registry record does not give the count at any individual draw, the concentration values, or a definition of what qualifies as a high level beyond the endpoint wording.
The threshold wording is not fully explained in the record: it names detectable concentrations and then gives <0.1 ug/mL. The assay’s detection limit, handling of values below that limit, and rationale for the cutoff are not reported in the registry record. Without the per-draw results and measurement details, the endpoint definition alone does not establish how often concentrations were detected or how they changed over time.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies the primary outcome but does not report its results. It therefore does not establish how many participants had detectable serum lidocaine concentrations at any particular blood draw, whether counts changed over the procedure, or whether any concentration remained high. The endpoint’s stated timeframe is 6 hours, but the exact measurement schedule and results within that period are not reported in the registry record.
Some event counts are recorded under the grouping Detectable Lidocaine Concentrations at Each Blood Draw: 0 serious events among 19 at risk and 2 other events among 19 at risk. These are the values in the record’s serious and other event fields. The record does not identify the two other events or clarify how these fields relate to the primary endpoint. The serious-event terms are not listed. The event counts should not be treated as the missing primary outcome results.
The study is cross-sectional and has no randomized comparator described. Measurements taken at different stages can provide observations about the participants who were sampled, but do not by themselves estimate a contrast against an untreated or otherwise comparable group. They also do not establish that a change in concentration was caused by a particular component of care. The timing of injections, surgery, and blood draws would matter for interpretation, but the detailed schedule is not reported in the registry record.
The outcome is a participant count at each draw. To interpret those counts, readers would need to know how many participants contributed a sample at each time, how missing samples were handled, and whether measurements from the same participant were accounted for in the analysis. These details are not reported in the registry record. The per-protocol population is named, but its inclusion criteria and size are not stated.
The record lists enrollment as 19, while its study description refers to 10 subjects. That discrepancy makes it especially important not to infer the denominator for each primary outcome measurement from the enrollment figure alone. The available serious and other event denominators are both 19, but they do not demonstrate that all 19 had complete primary endpoint measurements.
The registry describes planning calculations as illustrations based on the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. Those are planning assumptions, not evidence that this study used such an analysis or had a randomized two-arm design. Planning sample sizes are not observed power. The registry does not report the underlying primary outcome results or a sponsor analysis that could be interpreted as a comparative finding.
Overall, the posted record supports a description of the study question, setting, endpoint definition, and limited event counts. It does not support a conclusion about the frequency or duration of detectable concentrations, clinical symptoms, or a causal treatment effect. Those conclusions require outcome and measurement details that are not reported in the registry record.
9. Statistical Methods Explained
The central statistical issue is that this study describes repeated blood measurements in a surgical setting, not a randomized comparison. General statistical concepts can help explain what the endpoint could show, but the registry record does not provide enough results or analysis detail to reconstruct an estimate.
What does a participant count at each draw represent?
The primary outcome is a count of participants meeting a concentration criterion at each blood draw. In general, a count is most interpretable when its denominator is clear: readers need to know how many participants were eligible for that measurement and how many actually contributed a usable sample. The enrollment figure alone does not establish the denominator at each draw. The registry record does not report per-draw counts, denominators, or missing-sample handling.
Repeated measurements from one person are statistically related. In general, a person’s measurements across time are not independent observations, because they share characteristics and are collected within the same individual. An analysis comparing several draws should account for that within-person structure if it aims to estimate a time pattern or test differences. The registry lists no analyses, and a method for handling repeated measurements is not reported in the registry record.
How should the concentration threshold be read?
The endpoint title describes detectable serum lidocaine concentrations and includes the threshold <0.1 ug/mL. A threshold turns a concentration measurement into a classification, such as whether a participant meets a stated criterion. In general, such a classification can be easier to summarize than a full concentration distribution, but it discards information about how far measured concentrations lie from the cutoff. Interpretation also depends on the assay and on how results below its detection limit are treated.
The registry does not report the assay method, its detection limit, the reason for selecting the threshold, or how measurements at or around the boundary were classified. It also does not provide continuous concentration values. Consequently, the threshold’s analytical meaning cannot be evaluated from the registry record alone. The wording should be retained as registered rather than assumed to have a different inequality or interpretation.
What does a confidence interval add?
In general, a confidence interval expresses the uncertainty around an estimated quantity under the assumptions of the analysis. For a participant proportion or count, an interval can show that the estimate is compatible with a range of values rather than being known exactly. Its interpretation depends on the model, sampling process, and denominator. The registry record does not report a confidence interval for the primary endpoint, and there are no per-draw results from which one could interpret an interval.
With repeated measurements, an interval for a difference between draws would also need to reflect that measurements come from the same people. A simple calculation treating every blood draw as an independent participant could misstate uncertainty. The registry does not say whether any such comparison was performed; it lists no analyses.
Why can variation exceed a simple model’s expectation?
General statistical models for counts or proportions make assumptions about how observations vary. Over-dispersion means the observed variation is greater than the model expects. If present, a model that ignores it can produce uncertainty estimates that are too narrow. In repeated-measurement data, participant-to-participant differences and dependence across draws can contribute to extra variation. The registry provides no results that permit an assessment of over-dispersion, and it does not report a model or diagnostic checks.
The endpoint is a count at each draw rather than a stated count of events over person-time. Time-to-event methods therefore cannot be assumed to apply. The record gives a 6-hour timeframe but no event-time outcome, censoring information, or time-to-event analysis.
What do the planning assumptions mean?
The registry’s planning note describes illustrative sample-size calculations based on the observed effect, a stated fraction of that effect, a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. Such calculations answer a hypothetical planning question: how many participants might be needed under the specified assumptions to detect a chosen effect with a chosen power. They do not describe the actual design unless the trial record says those assumptions were used to plan and conduct the study.
Here, the registry identifies a non-randomized study and does not describe two like-for-like arms. Accordingly, equal allocation is an assumption for a planning illustration, not a description of the observed study groups. Sample-size illustrations are not observed power and cannot supply missing primary outcome findings. The record does not state a sample-size justification for the actual study or a prespecified effect to detect.
More broadly, the record does not provide a statistical analysis plan, hypothesis-testing procedure, confidence intervals, adjustment strategy, or detailed analysis population. These absences do not imply that no methods were used; they mean the methods are not reported in the registry record. The endpoint definition and design can be described, but a numerical assessment of precision or model adequacy is not possible without the omitted results and analytic details.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists one outcome measure and no analyses. It does not report a multiplicity plan or say whether additional outcomes, time points, or statistical tests were prespecified. When several outcomes or repeated time points are tested, general statistical practice recognizes that the chance of at least one apparently notable result can increase. Whether that issue arose in this study cannot be determined from the registry record.
The primary analysis population is described as per protocol, but the criteria for that population and its size are not reported. The record does not explain whether any participants were excluded after enrollment or how protocol deviations were handled. It also does not state how incomplete blood draws, unusable samples, or missing questionnaire responses were managed. These details matter because the available participants could differ across measurement times.
The enrollment figure is 19, whereas the study description refers to 10 subjects. The reason for the difference is not reported in the registry record. The serious and other event fields each list 19 at risk, but those denominators do not establish the number included in each primary endpoint analysis.
No imputation method, sensitivity analysis, or missing-data assumption is reported in the registry record. There is also no stated method for accounting for repeated measurements, no reported confidence interval, and no analysis output. It is therefore not possible to assess the impact of missingness, the handling of multiple comparisons, or the robustness of the primary analysis from the registry entry.
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 |
|---|---|---|---|
| Detectable Lidocaine Concentrations at Each Blood Draw | 0 | 19 | 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 |
|---|---|
| Detectable Lidocaine Concentrations at Each Blood Draw | 2 of 19 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Detectable Lidocaine Concentrations at Each Blood Draw |
|---|---|---|
| Headache | Surgical and medical procedures | 1 of 19 |
| Shaky | Surgical and medical procedures | 1 of 19 |
The registry’s event fields list 0 serious events among 19 at risk and 2 other events among 19 at risk for the grouping titled Detectable Lidocaine Concentrations at Each Blood Draw. These counts should be read as registry entries, not as a complete description of clinical safety. The two other events are not identified, and the serious-event terms are not listed. The deaths field is null, so deaths are not reported in the registry record rather than documented as zero.
The group title links the entry to detectable lidocaine concentrations, but the record does not explain how that grouping relates to adverse events or to the primary endpoint. The event counts do not report how many participants met the concentration criterion at each blood draw, and they do not describe symptoms, severity, timing, or attribution. The record also does not state whether events were actively sought or how they were classified. These fields therefore provide limited event-count information and should not be used to infer that concentrations did or did not produce systemic symptoms.
12. What the Result Does, and Does Not, Mean
The study addresses a specific measurement question: whether serum lidocaine is detectable around Mohs micrographic surgery on the face or neck, and whether high levels are sustained after local injection. The registry record identifies the population, the repeated blood-draw approach, and the endpoint’s stated threshold. It also reports limited event counts. Those elements describe what the study set out to examine, but the primary outcome results themselves are not reported in the registry record.
Without the counts at each draw, the concentration values, or the assay details, readers cannot determine the observed frequency, timing, or magnitude of detectable serum concentrations. The record also does not report symptom results, so the stated concern about systemic symptoms cannot be answered from the posted results. A null or absent primary result should not be inferred from the missing outcome information.
The non-randomized cross-sectional design can describe measurements in the observed surgical context, but it does not provide a randomized control comparison. It cannot, on its own, establish that a particular concentration pattern was caused by the injection or distinguish the role of other aspects of surgery. Exact timing and dose details are not reported in the registry record, further limiting interpretation of any potential temporal pattern.
The recorded enrollment of 19 and the summary’s reference to 10 subjects are both part of the registry record; the reason for the difference is not stated. Nor is the number contributing to each blood draw reported. Thus, neither the overall enrollment nor the event-field denominators should be substituted for missing primary endpoint denominators.
The responsible interpretation is narrow: the record documents a completed study designed to measure serum lidocaine around surgery and includes a small amount of event-count information, but it does not report the primary results needed to describe the observed concentrations. It therefore cannot support a conclusion about whether concentrations were detectable, sustained, or associated with symptoms.
13. Why This Trial Matters Statistically
This trial is statistically interesting because it focuses on repeated measurements within a surgical episode. The primary question is not simply whether a single concentration crosses a threshold; it concerns measurements before, during, and after local injection. A sound interpretation of such data depends on keeping the participant and measurement time distinct, and on recognizing that observations from the same participant are related.
The endpoint is also an example of how a continuous laboratory measurement can be reduced to a binary classification. That can make a result easier to communicate, but it places importance on the threshold, assay properties, and treatment of measurements near or below the detection limit. The registry states a threshold but does not report the supporting measurement details or primary counts. This illustrates why an endpoint definition is not a substitute for results.
The entry also highlights the difference between trial design and sample-size planning assumptions. The registry describes a non-randomized study without a like-for-like control comparison, while its planning note refers to equal allocation between two arms. That assumption is an illustrative calculation framework, not proof that two randomized arms existed or that the study had a comparative design. Planning estimates should not be mistaken for actual power or findings.
Finally, the record contains a difference between its enrollment figure and its summary’s stated subject count, as well as limited event counts without event terms. These features show why denominator clarity, population definitions, missing-data reporting, and complete outcome reporting are central to statistical interpretation. The design and registered question can be understood, but the primary concentration pattern cannot be assessed from the reported results.
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 main limitation for interpreting this study is that the registry record does not report the primary outcome values or participant counts at each blood draw. It therefore does not show the frequency or timing of detectable concentrations. The assay method, detection limit, concentration distribution, and reason for the threshold are also not reported, leaving the endpoint’s measurement properties unclear.
The registry lists enrollment as 19, while the study summary describes 10 subjects. The reason for this difference is not reported in the registry record. The per-protocol analysis population is named, but its size and criteria are absent. The number of participants with complete samples at each measurement time and the handling of missing or unusable samples are also not stated.
The record gives only broad timing language: blood draws occurred before, during, and after the procedure, with a 6-hour timeframe for the primary outcome. It does not provide exact draw times, lidocaine dose, injection details, or a more specific schedule. Those omissions limit assessment of the temporal pattern the study set out to examine.
There is no randomized comparator described, and allocation is not stated. The record lists no analyses and does not report a statistical analysis plan, methods for repeated measurements, confidence intervals, or a multiplicity strategy. Finally, the event fields do not name the two other events, and serious-event terms and deaths are not reported in the registry record. Together, these omissions restrict both statistical precision assessment and clinical interpretation.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Serum Concentration of Lidocaine After Local Injection During Mohs Micrographic Surgery — NCT00793169.
- Registry record last updated 2021-12-06; status last verified 2021-12.
- Results first posted 2010-11-30.
- 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
This completed cross-sectional study, sponsored by Northwestern University, concerns serum lidocaine measurements around Mohs micrographic surgery on the face or neck. The registry lists basal cell carcinoma and squamous cell carcinoma as conditions, enrollment of 19, a start of 2007-09, and primary completion of 2008-07. The study description refers to 10 subjects, and the reason for the difference from the enrollment figure is not reported in the registry record.
Blood was drawn before, during, and after surgery. The primary endpoint counts participants with the stated detectable concentration criterion at each draw over 6 hours, and the population note says the analysis was per protocol. The primary outcome counts and concentration results are not reported in the registry record. Event fields list 0 serious events and 2 other events among 19 at risk; the other events are not identified. No randomized comparator or analysis results are reported.