Treating Kidney Donors With Valganciclovir to Reduce Viral Transmission to Recipients: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Treating Kidney Donors With Valganciclovir to Reduce Viral Transmission to Recipients (NCT01329185), a randomized phase 2 study. The primary outcome is Incidence of EBV or CMV Related Disease in Transplant Recipient.

2. Clinical Question

The study rationale was that reducing viral transmission from donor to recipient might reduce viral infection or disease after transplantation. The brief summary describes a hypothesis about reducing EBV and CMV viremia during the first year after transplantation. The registered primary endpoint is narrower in a different way: it counts recipients with EBV- or CMV-related disease. Viremia and clinically related disease are not interchangeable outcomes, so the endpoint should be interpreted according to the disease-incidence definition in the registry record.

The posted primary outcome records 2 participants with an event in the placebo group and 0 in the valganciclovir group. Those counts describe the recorded outcome; they do not by themselves establish the size or precision of a treatment effect. A two-arm binary comparison is marked as not estimable in the registry record. Separate results for EBV and CMV, or for viremia apart from disease, are not reported in the registry record.

3. Trial Design

This was a phase 2, randomized, parallel-group, placebo-controlled study with quadruple masking. The registry record identifies University of Minnesota as the sponsor and lists the study as completed. Enrollment is reported as 17. The study began in 2011-06, and primary completion is recorded as 2014-04.

Randomization assigned eligible consenting kidney transplant donors to valganciclovir or placebo before transplantation. The intended treatment period was 14 days before transplant. The active regimen is listed as 450mg of valganciclovir twice a day; the placebo regimen is one placebo in the morning and one in the evening. The registry record describes donors as the people receiving the assigned study medication and transplant recipients as the people whose viral outcomes were assessed.

In general, random assignment is used to make treatment groups comparable, on average, with respect to characteristics that could affect outcomes. Masking is intended to limit the influence of treatment knowledge on care, outcome assessment, or reporting. The registry record labels the study quadruple masked, but it does not report which roles were masked or how masking was maintained.

The posted outcome counts are 2 events among 10 participants in the placebo group and 0 among 7 participants in the valganciclovir group. These are the group counts relevant to the posted primary outcome; they should not be read as a complete account of follow-up or as proof that every assigned donor-recipient pair contributed an outcome. The analysis population and the handling of participants without outcome data are not reported in the registry record.

The record does not report the randomization sequence method, allocation concealment procedure, eligibility criteria in detail, or the planned sample-size justification. It also does not report a statistical analysis plan. These omissions limit assessment of implementation and of whether the posted outcome analysis followed a prespecified plan.

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

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.

Population: Eligible kidney transplant donors were enrolled at the University of Minnesota Medical Center.

6. Primary Endpoint

The registry lists the primary outcome as Incidence of EBV or CMV Related Disease in Transplant Recipient, measured over At least 1 year.

The primary endpoint is the incidence of EBV- or CMV-related disease in transplant recipients of enrolled donors. The registry defines the measure as the number of participants with the outcome, gives the unit as participants, and lists the timeframe as at least 1 year. The posted counts are 2 in the placebo group and 0 in the valganciclovir group.

A binary disease endpoint represents whether a participant met the recorded outcome definition during the stated observation period. In general, a disease endpoint can be more directly relevant to clinical consequences than detection of a virus alone, while viremia can capture viral presence without necessarily indicating related disease. The registry record does not provide a detailed diagnostic definition, adjudication procedure, or separate counts for EBV-related and CMV-related disease.

The brief summary describes an aim to reduce both EBV and CMV viremia in the first year after transplantation. However, the registered primary outcome is disease incidence, not a separately reported measure of viremia. That distinction matters when interpreting what the results address: the posted primary counts concern the combined EBV- or CMV-related disease endpoint. They do not show how many events were attributed to each virus, whether a participant had viremia without disease, or the timing of any event.

The registry record does not report whether every participant was followed for the full timeframe, how incomplete follow-up was handled, or whether the outcome was assessed using a prespecified blinded process. The available counts therefore describe the posted endpoint but leave important details about its measurement and ascertainment unclear.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical interpretation begins with identifying the outcome, the groups being compared, and the unit of analysis. Here, the primary outcome is a count of participants with EBV- or CMV-related disease, and the registry describes it as a binary endpoint. The treatment assignment was made to donors, while the outcome was measured in transplant recipients. The posted result gives the outcome count and group size for each assignment group, but the registry record does not explain whether any donor-recipient linkage or clustering was considered in the analysis.

What does a binary outcome comparison usually estimate?

In general, a binary comparison can describe how often an outcome occurred in each group and estimate a contrast between those groups. Depending on the analysis plan, that contrast could be expressed on an absolute or relative scale. These are different summaries: an absolute contrast describes a change in event probability, while a relative contrast compares event occurrence proportionally. The registry record does not report a comparative estimate on either scale for this outcome. No such estimate should be reconstructed from the posted counts when the record itself marks the comparison as unavailable or not estimable.

In general, estimates are more informative when accompanied by uncertainty intervals. A confidence interval reflects the range of values compatible with the observed data under the assumptions of the statistical method. It is not a guarantee that the true effect lies within that range, and its width depends on the amount and pattern of information in the data. No confidence interval for the primary comparison is reported in the registry record, so the precision of a treatment contrast cannot be assessed from an interval.

Why can sparse outcomes make comparison difficult?

General statistical methods for binary outcomes rely on information from the observed events and non-events. When events are uncommon or absent in a group, some common estimation procedures can become unstable or fail to produce a finite estimate. Different methods can behave differently in this situation, so the choice of method matters. The registry record does not identify a method for sparse data, explain the reason the comparison was not estimable beyond its stated notice, or report an alternative analysis. This is why the count of zero in one group should be described literally rather than turned into a claim of no risk or a precise relative effect.

Randomization supports a fair comparison by assigning treatment independently of participants' prognostic characteristics in expectation. It does not guarantee that the groups will be identical, particularly when enrollment and event counts are limited. In general, prespecified adjustment can account for selected baseline factors, but adjustment requires a stated model and appropriate data. The registry record does not report baseline characteristics, an adjustment set, or an adjusted outcome model.

What do the planning assumptions mean?

The registry's sample-size assumptions describe planning illustrations computed from the observed effect. They specify a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect to detect described as a fraction of the observed effect. These assumptions explain a calculation framework, not the original design rationale. The registry record does not report the trial's own sample-size justification or any numerical planning result in the registry record for interpretation.

In general, a planning calculation asks how much information a future study might need under chosen assumptions. It depends on the selected effect, variability or event frequency, significance level, allocation, and analysis method. When the observed effect is based on sparse data or cannot be estimated reliably, a calculation anchored to it may be especially uncertain. A planning illustration is not a measure of the probability that the completed study detected an effect. It is not observed power, and it does not replace a reported effect estimate with uncertainty.

What can be inferred from the registry analysis fields?

The record reports one primary outcome measure and no secondary outcomes posted. It reports no analyses for the primary endpoint and marks a two-arm binary comparison as missing or not estimable. These entries distinguish outcome reporting from inferential reporting: group counts are posted, but a statistical comparison is not. The registry record does not state whether analyses were conducted but omitted, whether the comparison could not be fitted, or whether another analysis was planned.

General statistical reporting is strongest when it identifies the analysis population, outcome definition, estimator, model assumptions, missing-data approach, and uncertainty measure. Those details allow readers to assess whether the method matches the design and whether the result is robust to assumptions. The registry record does not report these details. Accordingly, the most defensible statistical description is the posted group counts, the recorded endpoint and timeframe, and the explicit absence of an estimable two-arm comparison.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Placebo", "Valganciclovir")
n      <- c(10, 7)
events <- c(2, 0)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Placebo  10  2  20.0  2.5  55.6  5.7  51.0  6.0  51.8
ARM  Valganciclovir  7  0  0.0  0.0  41.0  0.0  35.4  0.3  36.9

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists one primary outcome measure and no secondary outcomes posted. It does not report a multiplicity adjustment or explain whether additional outcomes or analyses were considered outside the posted results. Without that information, it is not possible to assess how the primary outcome was positioned among any broader set of planned comparisons. The absence of posted secondary outcomes should not be taken to mean that no other outcomes were collected.

The record does not describe missing-data procedures, participant flow, exclusions from analysis, or follow-up completeness. It also does not identify an analysis population such as all randomized participants or participants with observed outcomes. Those details matter because a result based on all assigned participants can differ from one restricted to participants with available outcome data. The posted group counts are not enough to determine which approach was used.

In general, missing outcome data can affect a comparison if the likelihood of missingness differs between groups or is related to the outcome. Methods for handling missing information depend on the data and assumptions; no particular method can be attributed to this study from the registry record. The timeframe is listed as at least 1 year, but the record does not report the completeness or duration of individual follow-up.

The registry record reports no analyses and states that values are missing or not estimable for a two-arm binary comparison. It does not report whether an analysis was attempted, what prevented estimation, or whether a prespecified alternative was used. These omissions limit assessment of multiplicity, missingness, and the population underlying the posted counts.

12. 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.

Most frequent non-serious adverse event terms

The registry's serious adverse event figures list 0 affected participants among 10 at risk in the placebo group and 0 affected among 7 at risk in the valganciclovir group. These figures describe the serious adverse events recorded in the posted safety results; they do not establish that the risk of serious harm is absent. The registry lists no top serious adverse event terms.

The separate figures for other adverse events list 2 affected participants among 10 at risk in the placebo group and 0 affected among 7 at risk in the valganciclovir group. These counts should not be combined with the primary disease endpoint: they are safety entries, not counts of EBV- or CMV-related disease unless the registry explicitly identifies them that way. The record does not provide event descriptions or severity details for these other events.

Death figures are not reported in the registry record. Nor does the record provide enough detail to establish how adverse events were defined, collected, or attributed to treatment. With no serious events recorded in either group, the posted figures are limited descriptive information rather than a precise comparison of safety between regimens.

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

The result establishes what the registry record reports for the primary endpoint: 2 participants in the placebo group and 0 in the valganciclovir group had EBV- or CMV-related disease. It also establishes that the record does not provide an estimable two-arm binary comparison. That combination supports a descriptive account of the recorded outcomes, not a precise estimate of the treatment contrast.

The counts do not show how much the underlying chance of disease may differ between groups. They do not show whether the apparent pattern is compatible with chance variation, nor do they quantify uncertainty with a confidence interval or test. The zero-event count in one group is not proof that events cannot occur under that regimen. The missing comparative estimate is especially important when interpreting a small number of recorded events.

The outcome concerns EBV- or CMV-related disease in recipients, not necessarily every instance of viral transmission or viremia. The brief summary describes an aim involving viremia, while the registered primary outcome measures disease. Separate virus-specific results and viremia results are not reported in the registry record. The posted primary outcome therefore cannot establish what happened for EBV and CMV separately.

The record also does not establish that every participant had complete follow-up for at least 1 year, nor does it report the analysis population, missing-data handling, detailed outcome criteria, or adjusted analyses. Randomization and masking are features of the registered design, but the registry record does not supply enough implementation and analysis detail to evaluate their conduct fully.

In general, a study's observed result is evidence about the participants and outcomes recorded, interpreted through its design and analysis. It is not a guarantee of the same result in other populations or settings. The posted data should be read as limited descriptive evidence, with the absence of a comparative estimate and the unreported analysis details kept in view.

14. Why This Trial Matters Statistically

This study raises a design and analysis question that is statistically important: an intervention is given to donors, while the primary clinical outcome is measured in recipients. In general, this structure requires clear linkage between donor treatment assignment and recipient outcome, and a transparent account of which participants contribute to each analysis. The registry record identifies the donor treatment and recipient endpoint but does not describe the linkage or analysis details.

The primary outcome is binary and the posted event counts are sparse. Such data make it important to report both the observed counts and an appropriate estimate of uncertainty. The registry record gives the counts but does not provide an estimable two-arm comparison. This illustrates why descriptive event totals alone may be insufficient for assessing the magnitude and precision of an effect.

The distinction between viremia and disease is also statistically consequential. A trial can have a stated biological or virological aim and a registered primary clinical endpoint that measures a different outcome. Readers need to know exactly which outcome was analyzed, whether components were combined, and whether component-specific results are available. Here, the posted primary measure combines EBV- or CMV-related disease, while separate virus-specific and viremia results are not reported in the registry record.

Finally, planning calculations and trial findings serve different purposes. The registry describes planning assumptions based on the observed effect, but such illustrations cannot replace a prespecified design justification or compensate for the unavailable comparison. Clear reporting of sample-size rationale, analysis methods, missing data, and uncertainty would help readers evaluate how much the evidence can support. This record shows why transparent registration and complete outcome reporting are central to statistical interpretation.

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 specific to this registry record constrain interpretation. The primary outcome is reported as a combined EBV- or CMV-related disease measure, with no separate counts for the two viruses. The brief summary refers to viremia, but results for viremia are not reported in the registry record. The diagnostic definition and outcome-assessment procedures for related disease are also not described.

The primary result consists of 2 events in the placebo group and 0 in the valganciclovir group, and the registry marks the binary comparison as not estimable. No effect estimate, confidence interval, or test result is reported. This prevents evaluation of the size and precision of a between-group difference from the posted record.

The registry record does not report the original sample-size justification, the statistical analysis plan, the analysis population, participant flow, missing-data procedures, baseline characteristics, or details of follow-up completeness. Although the primary timeframe is listed as at least 1 year, individual follow-up information is not reported. The record also does not explain which roles were masked or how masking was implemented.

Safety reporting is limited: serious adverse event counts and other adverse event counts are listed, but event descriptions and deaths are not reported in the registry record. These details are important for interpreting safety patterns and cannot be inferred from the event counts alone.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Treating Kidney Donors With Valganciclovir to Reduce Viral Transmission to Recipients — NCT01329185.
• Registry record last updated 2019-11-01; status last verified 2019-10.
• Results first posted 2014-06-20.
• 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

The registry record describes a completed phase 2, randomized, parallel, quadruple-masked, placebo-controlled study sponsored by University of Minnesota. Enrollment is reported as 17. The study began in 2011-06, with primary completion recorded as 2014-04.

Kidney transplant donors received valganciclovir or placebo for 14 days before transplantation. The primary outcome was the incidence of EBV- or CMV-related disease in transplant recipients at least 1 year after transplantation. The posted count was 2 in the placebo group and 0 in the valganciclovir group.

The registry record does not report an estimable two-arm binary comparison, a confidence interval, or a test result. It lists no secondary outcomes posted and does not report the analysis population or missing-data approach. The posted results therefore support a descriptive account of the primary outcome counts, with substantial limits on comparative statistical interpretation.