FDG Uptake in Vaginal Tampons is Due to Urine: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for FDG Uptake in Vaginal Tampons is Due to Urine (NCT01215318), a randomized na study. The primary outcome is Number of FDG Positive Tampoons.

2. Clinical Question

The clinical question concerns whether modifying a vaginal tampon is associated with a different frequency of FDG-positive tampons during FDG PET/CT examinations. The registry identifies urinary contamination as a possible explanation for FDG uptake and describes the study aim as determining the artifact’s etiology and identifying ways to prevent it. The posted primary outcome counts tampons with an SUV > 3.

This framing describes an outcome comparison, not proof of the biological source of uptake. A difference in the count could be compatible with a role for tampon modification, but the count alone does not identify the material or process responsible for FDG uptake. The registry also records tampon position relative to the pubococcygeal line as a secondary outcome, allowing a separate description of position by group.

3. Trial Design

The registry describes a randomized, double-masked, parallel-group study marked completed. It lists an enrollment of 44 and the condition Cancer. The recorded start date is 2010-02-02, and the primary completion date is 2010-08-02. These dates describe the registry record; further information about recruitment or conduct is not reported in the registry record.

The two groups used modified or unmodified vaginal tampons during FDG PET/CT. The intervention is classified as a device, and the intervention name is modified vaginal tampon. The arm descriptions distinguish patients using modified vaginal tampons from patients using unmodified vaginal tampons. The registry does not describe how the modification was made, how randomization was implemented, or which people were masked. Those procedural details are not reported in the registry record and should not be inferred from the design labels.

The primary outcome is a count of FDG-positive tampons using the stated SUV > 3 threshold, with a timeframe of 1 month. The only posted secondary outcome is tampon position relative to the pubococcygeal line, recorded in millimeters over the same timeframe. The registry lists Irene Burger as sponsor. Phase is recorded as NA, which does not supply a clinical phase classification.

The design labels describe the intended comparison, but they do not establish that every planned method was followed as intended. Details such as the allocation procedure, analysis population, missing-outcome handling, prespecified statistical methods, and any interim analyses are not reported in the registry record. The posted outcome values can therefore be described, while conclusions about unreported design and analysis decisions remain limited.

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: Women with urogenital carcinoma were excluded.

Overall Study

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.

6. Primary Endpoint

The registry lists the primary outcome as Number of FDG Positive Tampoons, measured over 1 month.

The primary endpoint is the number of FDG-positive tampons, with a positive tampon defined in the registry as having an SUV > 3. SUV is the uptake measure named in the endpoint definition. The registry gives a 1 month timeframe. This count operationalizes FDG uptake as a threshold-based outcome: each tampon is classified according to whether its SUV crosses the stated cutoff, and the recorded result is the number meeting that definition.

A threshold can make an outcome easier to interpret as a count of positive observations, but it also discards information about how far individual values lie above or below the cutoff. The record does not report individual SUV values, the distribution of uptake measurements, or a rationale for choosing the cutoff. It therefore does not show how robust the count would be to a different threshold.

The endpoint is relevant to the stated aim because the study concerns FDG uptake in vaginal tampons during PET/CT examinations. It can describe how often the defined finding was recorded in each group. By itself, however, the count does not establish the source of uptake or explain the mechanism. The registry does not report a primary statistical comparison, confidence interval, or p-value for this count outcome.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical information available for this study is uneven across outcomes. The primary endpoint is a count, but the registry does not report a statistical comparison for it. The secondary endpoint is continuous and has group means and standard deviations, from which an unadjusted mean-difference calculation is posted. The distinction matters: descriptive values show what was recorded, while an inferential estimate adds an expression of uncertainty under specified assumptions.

What does a confidence interval communicate?

General explanation: a confidence interval describes the uncertainty around an estimate using a method with stated statistical assumptions. A narrow interval indicates greater precision under those assumptions; a wide interval indicates less precision. It does not assign a probability that a particular fixed value is correct. For the secondary mean difference, the interval extends from -9.453 to 7.853 mm. Because it includes zero and values on either side, the data and calculation do not isolate a clear direction for the average difference. The interval should not be treated as an equivalence finding; equivalence requires a prespecified margin and a suitable analysis, neither of which is reported in the registry record.

What does the unadjusted recalculation mean?

The posted secondary comparison is a simple unadjusted recalculation from group summary statistics. It compares the reported average position in the two arms without adjustment for other variables. The estimate is -0.8 mm, and the reported unadjusted p-value is 0.856. These quantities describe the recalculation, not a sponsor-reported statistical analysis: the registry lists no reported analyses. No discrepancy is flagged in the record. The calculation does not establish that the groups were comparable on other characteristics, and it cannot account for covariates or analysis choices that are not reported.

General explanation: a p-value measures how incompatible the observed data are with a specified null model, assuming that model and the analysis assumptions apply. It is not the probability that the null hypothesis is true, a measure of clinical importance, or a measure of the probability that results will replicate. Interpretation also depends on the study design, analysis plan, data quality, and whether the result was selected from multiple examined outcomes.

Why does the endpoint type matter?

The primary endpoint is a count of tampons crossing a threshold. Count outcomes can have different statistical properties from continuous outcomes such as millimeter measurements. General explanation: count data may be more variable than a simple model expects, a property called over-dispersion. If over-dispersion is present and not handled appropriately, standard errors and confidence intervals from a model that assumes less variation may be misleading. The registry does not report a primary count model, a measure of dispersion, or a primary confidence interval, so it is not possible to assess how count variability was handled.

The primary measure also converts an uptake measurement into a positive-versus-not-positive classification. General explanation: thresholding can simplify interpretation, but it can make results sensitive to the chosen cutoff and removes information about the magnitude of measurements within each category. The registry states the SUV > 3 definition, but does not report a rationale for that threshold or an analysis using alternative thresholds. No conclusion about sensitivity to threshold choice can therefore be drawn from the record.

How should the planning illustrations be read?

The registry includes planning illustrations based on the observed secondary effect, under a stated two-sided significance level of 0.05, equal allocation, and a normal approximation. They describe participants per arm for 80% or 90% power when planning for 100%, 75%, or 50% of the observed effect. For 100% of the observed effect, the illustrations give 4,832 participants per arm for 80% power and 6,469 for 90% power. For 75% of the observed effect, they give 8,591 for 80% power and 11,500 for 90% power. For 50% of the observed effect, they give 19,328 for 80% power and 25,875 for 90% power.

These are planning illustrations computed from the observed secondary effect, not the trial’s own design justification. They do not describe the number enrolled or the number analyzed, and they are not observed power. The observed effect is itself uncertain, particularly given the broad confidence interval. Planning around a fraction of that estimate illustrates how sample-size requirements change when the target effect is smaller; it does not establish which effect size would be clinically important or expected in a future study.

The registry does not report a sample-size justification, a prespecified primary analysis, missing-data methods, interim analyses, or details of any adjustment for multiple outcomes. Such information is needed to evaluate whether the analyses followed a prespecified plan and how uncertainty was handled. Without it, the posted descriptive results and recalculated secondary comparison should be interpreted as limited evidence about the recorded outcomes, rather than as a complete statistical account of the trial.

10. Multiplicity, Missing Data and Analysis Populations

The registry records the primary count outcome and one secondary outcome, and it lists no reported analyses. It does not state whether the outcomes were prioritized through a prespecified testing hierarchy, whether any adjustment for multiple comparisons was planned, or whether additional outcomes or analyses were considered during the study. These details are not reported in the registry record. Without them, the weight to give an isolated secondary result is difficult to judge.

General explanation: when multiple hypotheses are tested, the overall chance of a false-positive result can rise if each test is interpreted independently. A multiplicity plan can define which outcome is primary, how secondary tests are ordered, or how significance thresholds are adjusted. The registry identifies a primary outcome, but does not report a broader testing strategy. This does not prove that no such strategy existed; it means it is unavailable in the record.

Information about missing data and analysis populations is also not reported in the registry record. The group records give outcome values and group sizes, but do not describe whether all randomized participants contributed data, whether any outcomes were unavailable, or how missing measurements were handled. No intention-to-treat, per-protocol, or other analysis population is identified. It is therefore not possible to evaluate the influence of exclusions or incomplete observations.

The record also does not report whether analyses were adjusted for baseline characteristics, whether the statistical methods were prespecified, or whether interim analyses occurred. Those omissions limit assessment of analytic flexibility and potential bias. They should be treated as gaps in the registry information, not as evidence that particular methods were or were not used. The primary count comparison lacks a reported inferential estimate, making these missing details especially relevant to interpretation.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The adverse-event records list zero serious adverse events and zero other adverse events in the modified-tampon group, with 20 at risk in each category. The unmodified-tampon group record likewise lists zero serious adverse events and zero other adverse events, with 24 at risk in each category. The deaths fields are not populated; death information is not reported in the registry record.

These figures describe what the registry records, not proof that no adverse events occurred. The record does not provide event definitions, ascertainment procedures, reporting windows, severity details beyond the serious-event grouping, or information about missing safety observations. It also does not describe whether the safety population matched the population used for the efficacy outcomes.

General explanation: a zero event count can occur when no events are observed or when event ascertainment and reporting do not capture events; the posted numbers alone cannot distinguish these possibilities. The figures should therefore be read as registry-reported counts within the stated at-risk groups, not as a comprehensive assessment of safety or evidence that either tampon type is free of risk.

12. What the Result Does, and Does Not, Mean

The registry documents a randomized comparison of modified and unmodified vaginal tampons during FDG PET/CT, with a primary outcome defined by a threshold for FDG uptake. The primary arm records contain different observed counts of FDG-positive tampons. The study’s stated purpose was to examine the source of the imaging artifact and possible means of prevention, but the posted primary data do not include a reported inferential comparison.

The secondary analysis describes tampon position and provides an unadjusted estimate with a confidence interval and p-value. That result does not establish a clear difference in average position, and it cannot explain the primary count pattern because no analysis relating position to uptake is reported. The statistical evidence available is therefore descriptive for the primary endpoint and limited for the secondary endpoint.

These results do not demonstrate that modified tampons prevent FDG uptake, establish that urine is the source of uptake, or show that tampon position causes the observed pattern. Such conclusions would require evidence beyond the posted group counts and the secondary summary comparison, including an appropriate analysis and information about the measurement and study procedures. The registry record does not report those details.

Nor does the absence of a clear secondary positional difference establish that the groups are equivalent. A nonsignificant result can reflect uncertainty, and the posted interval spans both negative and positive values. Equivalence would require a defined margin and an analysis designed to assess it; neither is reported in the registry record. In the same way, the lack of a primary p-value or interval does not permit a conclusion about statistical significance for the count outcome.

The most defensible reading is narrow: the record reports outcome counts and group summaries from a completed randomized study, while important inferential and methodological details are unavailable. The findings describe what was recorded in the trial, but do not settle the causal mechanism or provide a definitive estimate of the effect of tampon modification.

13. Why This Trial Matters Statistically

This trial is statistically instructive because it places a threshold-based count outcome beside a continuous secondary outcome. The primary measure is a count of observations meeting an SUV cutoff, while the secondary measure is a mean position in millimeters. Those outcomes require different summaries and potentially different statistical models. Treating them as interchangeable would obscure what each can answer.

The record also illustrates the difference between reporting observed values and reporting uncertainty. Group counts can show what was recorded, but a statistical comparison requires a method that reflects variability and the structure of the data. For the primary count, the registry does not report a comparison estimate or interval. Readers therefore cannot assess the precision of the group contrast from the posted record. The secondary outcome has an unadjusted recalculation, but its uncertainty must still be considered rather than relying on its point estimate alone.

Another relevant issue is the use of a cutoff. A threshold translates uptake measurements into a positive count, which may be useful for describing an imaging finding. At the same time, it hides variation within each classification and depends on the chosen threshold. The registry defines the cutoff but does not report why it was selected or whether results were examined under other definitions.

Finally, the planning illustrations show why sample-size planning depends on the effect size one aims to detect. They are based on the observed secondary effect and are explicitly planning calculations, not a record of the trial’s design rationale or an estimate of observed power. This distinction matters because an unstable observed estimate should not be mistaken for a reliable planning target.

In combination, these features make the study a useful example of why readers need the outcome definition, analysis method, uncertainty estimate, and missing-data information—not only arm-level values—to evaluate clinical research 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.

Several limitations specific to this record constrain interpretation. The primary outcome is reported as group counts, but no two-arm inferential comparison is available. The registry notes that values were missing or not estimable for a two-arm comparison of this count outcome. Consequently, there is no reported primary effect estimate, confidence interval, or p-value with which to assess precision or statistical compatibility with a null comparison.

The endpoint is defined using SUV > 3, but the record does not report individual SUV measurements, the rationale for the threshold, or sensitivity analyses using other thresholds. A threshold-based count cannot show how far observations were from the cutoff. The record also does not describe the modification itself in enough detail to assess which features might influence uptake or contamination.

Participant eligibility, baseline characteristics, randomization procedures, masking procedures, and the analysis population are not reported in the registry record. Missing-data handling and the timing and completeness of outcome assessment are also not described. These omissions prevent assessment of balance between groups, potential selection effects, and the consequences of incomplete observations.

The secondary result is an unadjusted recalculation from summary statistics, and the registry lists no reported analyses. No multiplicity approach or prespecified analysis plan is reported. The study’s relatively limited posted information means the secondary comparison cannot establish a mechanism, and it does not compensate for the absent primary comparison. The record also does not report a sample-size justification, so the relationship between the enrollment and the intended precision or power cannot be assessed.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: FDG Uptake in Vaginal Tampons is Due to Urine — NCT01215318.
• Registry record last updated 2019-08-28; status last verified 2019-08.
• Results first posted 2019-08-28.
• 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.

18. Record Summary

NCT01215318 is a completed randomized, double-masked, parallel-group study of modified versus unmodified vaginal tampons during FDG PET/CT. The registry lists Cancer as the condition, an enrollment of 44, Irene Burger as sponsor, a start date of 2010-02-02, and a primary completion date of 2010-08-02.

The primary outcome counts tampons with SUV > 3 over 1 month. The arm records report 2 positive tampons for modified tampons and 10 for unmodified tampons, but no inferential comparison is reported for this count outcome. The one secondary outcome is tampon position relative to the pubococcygeal line; an unadjusted recalculation is reported with a wide confidence interval. Analysis methods, missing-data handling, analysis populations, and multiplicity procedures are not reported in the registry record.

Overall, the posted record provides descriptive outcome information but limited evidence for a causal or mechanistic conclusion.