Vitamin B12 and Folate Administration on Homocysteine Concentrations After Nitrous Oxide Anesthesia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Vitamin B12 and Folate Administration on Homocysteine Concentrations After Nitrous Oxide Anesthesia (NCT00901394), a randomized na study. The primary outcome is Change in Plasma Total Homocysteine Concentration (tHcy).

2. Clinical Question

The registry frames the question around whether B-vitamins before nitrous oxide anesthesia prevent an increase in homocysteine. It also notes that homocysteine has been linked to cardiovascular complications. That rationale is not itself a trial result: the posted endpoint is a laboratory measurement, not a cardiovascular outcome.

The record reports one primary outcome and no secondary outcomes. It does not give a separately stated hypothesis for each pair of groups, nor does it report which specific contrasts were tested in the mixed-model analysis. Consequently, the clinical question can be described in broad terms, but the exact pairwise questions behind the reported test are not reported in the registry record.

3. Trial Design

The registry identifies this as a randomized, quadruple-masked, parallel-group trial. It lists enrollment as 63 and status as completed. The study start is recorded as 2009-03, with primary completion recorded as 2010-01. The phase is listed as NA. Washington University School of Medicine is named as sponsor.

Three groups are described: B12-folic acid with nitrous oxide, nitrous oxide with placebo, and an oxygen-nitrogen control group. The posted outcome data give group sizes of 20, 19, and 20, respectively. The registry does not report details of the randomization procedure, allocation concealment, masking procedures, or the way the anesthesia conditions were implemented. Those details are not reported in the registry record.

The primary outcome was change in plasma total homocysteine concentration, measured in mcmol/L. The registry describes the summary as a median with a 95% confidence interval. It defines change using baseline and the peak postoperative measurement, with the peak determined from the value within 30 minutes after anesthesia ended and the value on the morning of postoperative day 1.

The sponsor's analysis is described as a mixed models analysis involving the three groups, with a reported p <0.05. The record does not provide a model specification, an effect estimate for the overall test, or estimates for pairwise contrasts. Further details of the planned statistical analysis 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

Reasons for not completing this period:

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 Change in Plasma Total Homocysteine Concentration (tHcy), measured over Immediately postoperatively and on postoperative day 1.

The primary endpoint measures the change in plasma total homocysteine concentration from the preoperative baseline to the peak postoperative measurement. The registry defines that peak as the maximum of the measurement obtained within 30 minutes after anesthesia ended and the measurement taken on the morning of postoperative day 1. The unit is mcmol/L.

Homocysteine is the biological marker at the center of the study question. The registry's brief summary describes it as a metabolite linked to cardiovascular complications and frames the trial as testing whether B-vitamins before nitrous oxide anesthesia prevent its increase. Measuring the change allows the analysis to focus on postoperative movement relative to each participant's baseline rather than on a single postoperative concentration alone. That is a general explanation of why change-from-baseline outcomes may be used; the registry does not state a separate justification for choosing this endpoint.

The endpoint is reported as a median and a 95% confidence interval for each group. A median describes the middle of the observed distribution, while the confidence interval conveys uncertainty around the reported group summary under the analysis used. The record does not describe how those intervals were constructed or how repeated measurements were incorporated into the endpoint calculation beyond its definition of the peak.

This is a laboratory endpoint, not a direct measure of cardiovascular events or other clinical outcomes. The registry explicitly states that there were no secondary outcomes. It does not report an additional endpoint that would show whether any change in homocysteine was accompanied by a change in cardiovascular complications.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry reports a randomized, parallel-group design with quadruple masking. In general, random assignment is intended to make comparison groups similar, on average, with respect to factors known and unknown at the start of a trial. Masking is generally used to reduce the influence of expectations on care, measurement, or assessment. The record does not report the specific randomization or masking procedures, so their implementation cannot be evaluated from the registry entry.

What does the median describe?

A median is the middle value in an ordered set of observations. It can be useful when a distribution is skewed or contains extreme observations because it is less affected by unusually large or small values than an arithmetic mean. The registry identifies the primary summaries as medians, but does not describe the distribution of individual changes or explain why the median was selected.

What does a confidence interval convey?

A confidence interval gives a range of values compatible with the data and the method used to calculate the interval, under the assumptions of that method. A narrower interval generally indicates greater precision than a wider interval. The posted 95% confidence intervals accompany each group's median change. They are not intervals for between-group differences, and the registry does not specify how the intervals for medians were calculated.

For the control group, the reported interval extends from -0.8 to 1.9 mcmol/L; the intervals for the two nitrous oxide groups are reported as 0.2 to 3.6 and 0.6 to 4.8 mcmol/L. These intervals should be read as uncertainty around the respective group summaries, not as a direct comparison among groups. A confidence interval for a contrast would address a different question.

What does the mixed-model result mean?

A mixed model is a general statistical approach that can account for multiple sources of variation, including correlated observations when measurements are repeated on the same participant. The particular structure and assumptions depend on how the model is specified. The registry names a mixed models analysis, but the model terms, covariance structure, handling of repeated measurements, and adjustments are not reported in the registry record. It is therefore not possible to assess those details or reproduce the analysis from the entry.

The reported p <0.05 is evidence against the null hypothesis used for the sponsor's test, under the analysis assumptions. A p-value is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of an effect. Because the registry does not identify the exact hypothesis or provide its estimate, the p-value alone cannot tell readers which groups differed or by how much.

Why do pairwise comparisons matter?

An analysis involving three groups can address an overall question about group differences, or it can involve specific comparisons between selected groups. Those are not interchangeable questions. An overall test can indicate evidence of some group difference without identifying which groups account for it. Pairwise estimates, confidence intervals, and a clear description of the testing plan would help explain the pattern. The registry does not report those contrast estimates or specify the comparison structure.

General statistical practice also considers whether multiple hypotheses are tested, because conducting multiple tests can increase the chance of a false-positive result if no adjustment is made. Whether an adjustment was planned or applied is not reported in the registry record. No secondary outcomes are posted, but that alone does not disclose how comparisons within the primary outcome were handled.

How should planning illustrations be understood?

Sample-size calculations based on an observed effect are planning illustrations, not evidence that a completed trial had a particular probability of detecting an effect. The registry's stated illustration assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. For time-to-event calculations, the stated convention is to report a total number of events; other calculations use participants per arm. These assumptions describe planning calculations, not the trial's own design justification, which is not reported in the registry record. The registry does not report a sample-size justification or interim analyses.

General concerns about over-dispersion are relevant when observed variability exceeds what a statistical model assumes: uncertainty can then be understated if the model does not accommodate that extra variation. The registry does not report enough information about the model or data distribution to assess whether over-dispersion was relevant. That is a general methodological point, not a finding about this trial.

10. Analyses Reported by the Sponsor

The registry reports the sponsor's analysis as a mixed models analysis involving the three groups, with p <0.05. It does not provide a model estimate, a test statistic, an exact p-value, or a group-specific contrast. The result therefore supports only the statement that the reported analysis met its stated significance threshold; it does not quantify a particular between-group difference.

A recalculated two-arm estimate is not available in the registry record. The posted group medians and confidence intervals are not enough to reconstruct a valid contrast and its uncertainty. No independently recalculated effect estimate should be treated as a substitute for the sponsor's analysis. The registry does not flag a discrepancy between a sponsor analysis and a recalculation.

For interpretation, the sponsor's reported analysis remains the inferential result in the record, but its scope is limited by missing details about the hypothesis and model. The group summaries can be described on their own terms; they do not reveal which contrast produced the reported p-value.

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome and explicitly states that there were no secondary outcomes. It also lists one analysis. This gives a narrow outline of the posted outcome record, but it does not establish how many statistical tests were conducted or whether comparisons within the primary outcome were planned in advance.

Multiplicity arises when several hypotheses are tested. In general, more testing can increase the chance of obtaining at least one small p-value by chance, so a prespecified testing strategy or adjustment may be important. Whether the sponsor used a multiplicity adjustment, a hierarchical testing procedure, or another approach is not reported in the registry record. The reported p <0.05 should therefore be interpreted in light of the analysis that is described, without assuming an unreported adjustment or an unreported testing plan.

The registry does not report the analysis population, the number of participants with endpoint measurements, or how missing measurements were handled. It also does not report whether participants were analyzed according to assigned group, whether any participants were excluded, or how deviations from the planned treatment were addressed. These details matter because missing data and analysis-population choices can affect both the estimated result and its uncertainty.

The endpoint uses baseline and postoperative measurements, including the morning of postoperative day 1. The record does not report the completeness of these measurements or explain how a peak was defined when one of the postoperative measurements was unavailable. The mixed-model method is named, but its assumptions and missing-data handling are not described. No conclusion about the presence or absence of missing data can be drawn from the registry entry.

These reporting gaps do not demonstrate that the analysis was inappropriate. They mean that readers cannot fully assess the multiplicity strategy, reproduce the model, or evaluate the influence of missing observations from the registry record alone.

12. Safety Results

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

Deaths

Other (non-serious) adverse events

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

Most frequent non-serious adverse event terms

The registry reports serious adverse events as zero in each group. It lists 20 participants at risk in the B-vitamins plus nitrous oxide group, 19 in the nitrous oxide plus placebo group, and 20 in the nitrous oxide-free group plus placebo. Deaths are reported as zero in all three groups.

For other adverse events, the registry reports zero in the B-vitamins plus nitrous oxide group, 2 in the nitrous oxide plus placebo group, and 1 in the nitrous oxide-free group plus placebo. These are the posted event counts; they should not be interpreted as estimates of comparative risk. The record does not provide event descriptions for these non-serious events, their timing, severity, or the way they were collected. No serious adverse-event terms are listed.

Zero reported serious events does not establish that serious events could not occur, particularly in a trial of this size and with the follow-up described. Conversely, the nonzero counts do not establish that an intervention caused an event. The registry does not report a formal comparative safety analysis or enough detail to interpret differences in event ascertainment.

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

The results establish that the registry posted group-level medians for change in plasma total homocysteine, together with 95% confidence intervals, and that the sponsor reported a mixed-model analysis with p <0.05. The values describe the measured endpoint in the three trial groups. They do not supply a numerical estimate of the difference between any two groups.

The entry does not identify the exact hypothesis behind the reported p-value or give the model estimate and contrast-specific uncertainty. As a result, the evidence cannot be translated into a clear estimate of how much the vitamin group differed from either comparator. The p-value alone does not show the size, direction, or clinical importance of a specific contrast.

The trial's stated rationale concerns homocysteine and its link to cardiovascular complications, but the primary endpoint is homocysteine concentration. No secondary outcomes are reported, and the registry does not post a cardiovascular outcome result. A change in a laboratory marker should not be treated as evidence of a change in cardiovascular events.

The safety record reports no serious adverse events or deaths in the groups, alongside the listed counts of other adverse events. These descriptive counts do not by themselves establish comparative safety. The registry entry does not report enough information about event definitions, follow-up, or formal safety comparisons to support stronger conclusions.

More complete interpretation would require the model specification, the tested hypothesis, pairwise effect estimates with confidence intervals, and information about analysis populations and missing measurements. Those details are not reported in the registry record. The findings should therefore be understood as posted group summaries and an incompletely described inferential result, rather than as a definitive account of all treatment contrasts or clinical consequences.

14. Why This Trial Matters Statistically

This trial is statistically instructive because its reported inferential result is broader than the numerical summaries available for interpretation. The registry gives medians and confidence intervals for each group, then reports a mixed-model p-value for an analysis involving three groups. Without the tested hypothesis and contrast estimates, readers cannot connect that p-value to a particular pair of groups or quantify the size of a difference.

It also illustrates why confidence intervals around separate group summaries are not interchangeable with confidence intervals for comparisons. Each interval describes uncertainty around its own group's median. A treatment contrast has its own estimate and uncertainty, which depend on the comparison and analysis. The group summaries alone do not provide those quantities.

The endpoint focuses on a biological marker selected to address the study rationale, while the registry reports no secondary outcomes. That distinction matters statistically and clinically: a result for a laboratory measure does not, by itself, answer whether a clinical event changed. The posted record supports description of the marker, not a conclusion about cardiovascular outcomes.

Finally, a named method is not a full analysis plan. Mixed models can be specified in different ways, and interpretation depends on those choices, the handling of repeated measurements, and the handling of missing data. The registry's limited methodological detail makes the record a useful example of why model descriptions and contrast-specific estimates are important for evaluating trial results.

15. 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 are specific to what the registry reports for this trial. The population is not described beyond the anesthesia context, and eligibility criteria and participant characteristics are not reported in the registry record. Details of randomization, allocation concealment, and the masking procedures are also not reported, limiting assessment of how the design was implemented.

The primary endpoint is defined using the peak of two postoperative measurements, but the record does not describe measurement completeness, laboratory procedures, or the handling of unavailable values. It reports group medians and confidence intervals but does not state how the intervals were calculated. The reported mixed models analysis is not described in sufficient detail to reproduce or evaluate its assumptions.

The registry gives p <0.05 but does not identify the tested hypothesis, provide an effect estimate, or report pairwise contrasts. It also does not describe multiplicity handling. These omissions make it difficult to determine which group differences, if any, were supported by the reported test and how precisely they were estimated.

The analysis population and missing-data approach are not reported in the registry record. A sample-size justification and interim analyses are also not reported. The observed group summaries therefore cannot answer whether the study was designed around a particular target effect or how exclusions and missing observations may have influenced the analysis.

Safety reporting is limited to event counts and the absence of listed serious-event terms. Details about non-serious events and comparative safety analyses are not reported. Finally, no secondary outcomes are posted, so the record does not provide clinical outcome evidence beyond the homocysteine endpoint.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Vitamin B12 and Folate Administration on Homocysteine Concentrations After Nitrous Oxide Anesthesia — NCT00901394.
• Registry record last updated 2020-09-16; status last verified 2020-08.
• Results first posted 2020-09-16.
• 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.

19. Record Summary

NCT00901394 is a completed randomized, quadruple-masked, parallel-group trial sponsored by Washington University School of Medicine. The registry lists enrollment as 63 and the phase as NA. Study start is recorded as 2009-03 and primary completion as 2010-01.

The three groups received B12-folic acid with nitrous oxide, nitrous oxide with placebo, or oxygen-nitrogen with placebo. The primary outcome was change in plasma total homocysteine from baseline to the defined peak postoperative measurement, reported as a median with a 95% confidence interval. The sponsor's mixed models analysis is reported as p <0.05, without a stated contrast estimate or detailed model specification. No secondary outcomes are reported. Serious adverse events and deaths are listed as zero in all groups; other adverse-event counts are also posted.