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 BK Treatment Study (NCT01034176), a randomized phase 4 study. The primary outcome is Percent Change From Baseline in BK Virus Copies at 3 Months.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01034176 |
| Phase | Phase 4 |
| Condition | BK Viremia |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Quadruple |
| Enrollment | 43 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Brigham and Women's Hospital |
| Results posted | Yes |
2. Clinical Question
Population
The study concerned renal transplant recipients with BK viremia. The registry record describes persistent viremia in its hypothesis, but does not report a more detailed eligibility definition or the characteristics of participants who entered the study. Enrollment was 43. The primary outcome summaries include 20 participants in the levofloxacin arm and 19 in the placebo arm; reasons for the difference between enrollment and those outcome counts are not reported in the registry record.
Intervention
Participants assigned to levofloxacin received 500 mg every day for 30 days, with the dose adjusted for renal function. The registry describes the study drug as oral levofloxacin. This was compared with a placebo described as identical to levofloxacin and taken daily for 30 days.
Comparator
The comparator was placebo. The study used randomized allocation, quadruple masking, and a parallel-group model. The registry record does not specify the allocation procedure or describe which roles were included in the masking designation.
Primary question
The primary question was whether the arms differed in percent change from baseline in BK virus copies at 3 months. The stated measurement interval was baseline and 3 months, and the outcome description specifies BK virus copies per milliliter. The record’s hypothesis links levofloxacin treatment to a reduction or elimination of BK virus in blood, but the primary endpoint is a viral-copy measure, not a direct measure of kidney damage. The registry does not report a primary treatment-effect estimate with a confidence interval or a p-value.
3. Trial Design
The BK Treatment Study was registered as a phase 4, randomized, quadruple-masked, parallel-group trial. It compared levofloxacin with placebo in participants with BK viremia. The registry lists Brigham and Women's Hospital as sponsor and describes the study as multicenter in its official title. Enrollment was 43, and the status is completed. The start is recorded as 2009-02 and primary completion as 2012-06.
The levofloxacin arm received 500 mg every day for 30 days, with dose adjustment for renal function. The placebo was described as identical to levofloxacin and was taken daily for 30 days. The record does not report the actual allocation ratio, the randomization sequence method, concealment procedures, or which participants or study personnel were masked. Those details should not be inferred from the broad design labels.
The primary outcome was percent change from baseline in BK virus copies at 3 months. The registry gives a median as the outcome parameter and standard deviation as the dispersion measure. Primary outcome summaries are reported for 20 participants assigned to levofloxacin and 19 assigned to placebo. The record does not report how participants were handled in the analysis, whether the analysis followed intention-to-treat principles, or why the primary outcome counts do not cover the full enrollment.
One secondary outcome is listed, and the record reports no analyses under its reported analyses listing. The sample-size justification, planned analysis methods, stopping rules, and interim analyses are not reported in the registry record. The posted planning illustration is based on the observed secondary effect and should not be mistaken for the trial's original design calculation.
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 | Levofloxacin | Placebo |
|---|---|---|
| STARTED | 22 | 21 |
| COMPLETED | 20 | 19 |
| NOT COMPLETED | 2 | 2 |
Reasons for not completing this period:
| Reason | Levofloxacin | Placebo |
|---|---|---|
| Physician Decision | 2 | 0 |
| Withdrawal by Subject | 0 | 1 |
| Lost to Follow-up | 0 | 1 |
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 | Levofloxacin | Placebo | Total |
|---|---|---|---|---|
| Participants analysed | 20 | 19 | 39 | |
| Age, Continuous: Age at time of consent | years | 56.22 (32 to 74) | 54.9 (25 to 70) | 55.36 (25 to 74) |
| Sex: Female, Male: Female | Participants | 2 | 7 | 9 |
| Sex: Female, Male: Male | Participants | 18 | 12 | 30 |
| Region of Enrollment: United States | participants | 20 | 19 | 39 |
6. Primary Endpoint
The registry lists the primary outcome as Percent Change From Baseline in BK Virus Copies at 3 Months, measured over Baseline and 3 months.
| Element | Registry entry |
|---|---|
| Result type | Median |
| Measure of spread | Standard Deviation |
| Unit | Percent change of BK virus copies |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint measures percent change in BK virus copies per milliliter between baseline and 3 months. It is a virologic outcome: it describes change in the measured amount of virus in blood over the stated interval. The record's hypothesis proposes that levofloxacin might decrease or eliminate detectable BK virus in blood and thereby impair progression toward BK virus-induced kidney damage. The endpoint directly addresses the viral-copy component of that hypothesis, not kidney injury itself.
The registry reports a median percent change of 70.3 with a standard deviation of 42.5 in the levofloxacin arm, based on 20 participants. The placebo arm has a median of 69.1 and a standard deviation of 39.5, based on 19 participants. The record does not state the sign convention used for percent change. Therefore, the positive values alone do not establish whether they represent an increase or a decrease in viral copies. The summaries are numerically close, but the record does not report a direct primary comparison, confidence interval, or p-value.
A viral-copy endpoint can offer a measurable way to examine change in viremia. It should not be treated as interchangeable with a clinical outcome such as kidney damage. The registry record does not report a primary kidney-damage endpoint or establish how changes in viral copies correspond to such damage in this study.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The primary outcome summaries are similar in their reported central values: 70.3 for levofloxacin and 69.1 for placebo. The accompanying standard deviations are 42.5 and 39.5, respectively. These summaries describe the reported percent-change outcome in the participants included in each arm's primary results. They do not, by themselves, quantify the uncertainty in the difference between arms.
The registry specifies the median as the primary outcome parameter, while also giving a standard deviation as the measure of spread. A median describes the middle of an ordered set of observations; a standard deviation describes dispersion using distances from a mean. Without participant-level data or further methodological detail, the combination should be read as the registry's reported summary rather than as evidence of a particular analysis method. The record does not specify whether the reported medians were adjusted or unadjusted.
The direction of the primary outcome cannot be interpreted confidently from the positive values alone because the registry does not define the sign convention for percent change. The description says the outcome is percent change from baseline to 3 months, but does not say whether a positive value corresponds to more viral copies or fewer. This limits interpretation of the direction of change as well as any claim about which arm had a more favorable result.
No primary comparison estimate, confidence interval, or p-value is reported. Consequently, the posted primary summaries do not show how precisely the between-arm contrast is estimated, and they do not provide a formal test of whether the arms differ. The arm-level values should not be converted into a treatment-effect estimate by subtracting them or by treating the dispersion measures as confidence limits.
The secondary outcome is supported by an unadjusted comparison: the estimated risk difference is 0.066, with a confidence interval from -0.216 to 0.348 and an unadjusted p-value of 0.648. That interval includes values on both sides of no difference and spans a substantial range of possible effects. It therefore leaves considerable uncertainty about the direction and magnitude of the secondary contrast. It does not substitute for a primary-outcome analysis, which is not reported.
The trial enrolled 43 participants, while the primary summaries include 20 in the levofloxacin arm and 19 in the placebo arm. The reasons that outcome counts differ from total enrollment, and the handling of missing outcomes, are not reported in the registry record. With no reported primary inferential analysis, no stated analysis population, and incomplete information about outcome availability, the primary result should be interpreted as descriptive rather than as a conclusive estimate of comparative effect.
9. Statistical Methods Explained
The registry identifies this as a randomized, quadruple-masked, parallel-group study. Randomization is intended to make assignment independent of participants' prognosis on average, reducing systematic differences between treatment groups. Masking can reduce the influence of expectations on participant behavior, care, outcome assessment, or analysis. These are general statistical and design principles; the registry's broad labels do not specify how randomization or masking was implemented in this trial. Details of sequence generation, concealment, and the roles masked are not reported in the registry record.
What does the primary summary describe?
The primary outcome is percent change in BK virus copies from baseline to 3 months. The registry reports the median for each arm and a standard deviation. A median is a measure of central location that is less affected by extreme observations than a mean. A standard deviation describes how spread out observations are around their mean. Because the outcome parameter and dispersion measure summarize data in different ways, the pair does not reveal the full distribution, and the record does not explain the choice of these summaries.
Percent change requires a direction convention: positive values can have different meanings depending on how change is defined. The registry gives the baseline-to-follow-up description but does not define that convention. As a result, the reported positive median values cannot be translated into a direction of viral change using the record alone. Nor can the arm summaries establish a between-arm effect without a comparison estimate and an account of its uncertainty.
How should uncertainty be read?
A confidence interval is a range of estimates compatible with the observed data under the method used to construct it. In repeated use, a procedure with a stated confidence level has a long-run coverage interpretation under its assumptions; it is not a probability statement about a single fixed treatment effect. The primary outcome has no reported confidence interval, so its precision cannot be assessed from an interval estimate in the registry record.
For the secondary comparison, the registry reports a risk difference of 0.066 and a confidence interval from -0.216 to 0.348. The interval extends across zero, which represents no risk difference on that scale. Its width indicates that the estimate is compatible with a range of effects, including effects in either direction. The unadjusted p-value is 0.648. A p-value describes how unusual data at least as inconsistent with a specified null model would be if that model and the test assumptions held. It is not the probability that the null hypothesis is true, and it does not measure clinical importance.
The registry also gives risk-ratio and odds-ratio estimates for the secondary comparison. These are different ways of expressing relative group contrasts; unlike a risk difference, they compare risks proportionally or through odds. Their interpretation depends on the outcome definition and the underlying risks. They are secondary, unadjusted estimates, and should not be treated as confirmatory evidence independent of the other reported comparisons.
Why do planning illustrations differ from trial results?
Sample-size planning asks how many participants would be needed under specified assumptions to detect an effect at a chosen significance level and power. The registry's planning illustration uses the observed secondary effect, two-sided significance level 0.05, equal allocation, and a normal approximation. It presents participants per arm for 80% power and participants per arm for 90% power when planning for 100% of the observed effect, 75% of the observed effect, or 50% of the observed effect. The respective 80% planning figures are 735, 1,330, and 3,042 participants per arm; the corresponding 90% figures are 983, 1,780, and 4,072 participants per arm.
These are planning illustrations, not participants enrolled and not observed power. They use the observed effect as an input, so they do not establish what effect the original investigators expected or what sample size they planned before enrollment. The assumptions behind the trial's original sample-size calculation are not reported in the registry record. A planning calculation based on a noisy observed effect can be especially uncertain, because the observed effect may not represent the effect that would be seen in a larger study.
What is not established by the record?
The registry reports no primary analysis method, adjustment strategy, analysis population, missing-data method, or interim-analysis plan. It also does not report a statistical rationale for using the stated endpoint summaries or explain whether any model assumptions were checked. These omissions prevent a detailed appraisal of whether the analysis matched the original plan. General principles such as adjusting for baseline values, accounting for skewed outcomes, or addressing missing observations cannot be assumed to have been applied in this study.
For a two-group comparison, effect estimates and confidence intervals are generally more informative than a significance test alone because they convey both direction and precision. For a count or continuous outcome with unusually variable observations, the choice of summary and model can matter; over-dispersion, in general, means variability exceeds what a simpler model assumes and may make standard errors too small if ignored. The registry does not report a count model or an over-dispersion assessment for the primary outcome, and such methods should not be attributed to the study.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists one primary outcome and one secondary outcome, but does not report how the investigators planned to manage multiple statistical tests. Multiplicity arises when several outcomes, time points, subgroups, or analyses are examined: the chance of finding at least one apparently unusual result can increase as the number of tests grows. This general concern does not establish that a particular adjustment was required or omitted in the original protocol; the plan is not reported in the registry record.
The secondary comparison is unadjusted, and its p-value is 0.648. It should be interpreted as an unadjusted result rather than as evidence that accounts for a broader family of possible tests. No multiplicity-adjusted estimate or p-value is reported. The primary endpoint has no reported p-value or confidence interval, so the registry record does not allow readers to assess a primary inferential test alongside the secondary result.
Missing outcome data are also difficult to assess. The trial enrollment is 43, while primary outcome summaries list 20 participants in the levofloxacin arm and 19 in the placebo arm. The record does not explain the difference, report the number of missing primary outcomes, describe reasons for missingness, or state how missing observations were handled. It does not identify an intention-to-treat, per-protocol, or other analysis population. These details matter because analyses based on different participant sets can answer different questions and can be affected differently by missing data.
The registry does not report sensitivity analyses for missing outcomes, imputation methods, exclusions, or deviations from the assigned intervention. It also does not report interim analyses, stopping rules, or a statistical analysis plan. In the absence of those details, it is not possible to determine whether the posted results follow a prespecified analysis or whether all planned outcomes and analyses are represented.
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 |
|---|---|---|---|
| Levofloxacin | 1 | 20 | 5.0% |
| Placebo | 1 | 19 | 5.3% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Levofloxacin | 0 of 20 |
| Placebo | 1 of 19 |
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 |
|---|---|
| Levofloxacin | 2 of 20 |
| Placebo | 0 of 19 |
Most frequent serious adverse event terms
| Event term | Organ system | Levofloxacin | Placebo |
|---|---|---|---|
| Neoplasm, malignant | Neoplasms benign, malignant and unspecified (incl cysts and polyps) | 1 of 20 | 0 of 19 |
| suicidal ideation | Psychiatric disorders | 0 of 20 | 1 of 19 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Levofloxacin | Placebo |
|---|---|---|---|
| achilles tendon strain/injury | Musculoskeletal and connective tissue disorders | 2 of 20 | 0 of 19 |
Serious events with the highest arm-level rate: suicidal ideation (5.3%), neoplasm, malignant (5.0%).
The registry reports serious adverse events in 1 participant in each arm. For other adverse events, it reports 2 affected participants in the levofloxacin arm and 0 in the placebo arm. Deaths are recorded as 0 in the levofloxacin arm and 1 in the placebo arm. These are descriptive counts from the registry record; they do not establish that an event was caused by the assigned treatment.
The record also lists suicidal ideation at 5.3% and Neoplasm, malignant at 5.0% among its top serious-event terms. It does not specify the arm associated with either term, provide a corresponding event count in that listing, or explain the percentages' denominator. Those percentages therefore cannot be assigned to a treatment group from the registry information alone.
Safety counts should be read with attention to the number of participants at risk and to the trial's limited enrollment. Small counts can vary substantially by chance and do not provide a precise estimate of event frequency. The registry does not report event timing, severity details beyond the serious-event classification, relationship to study drug, or withdrawals due to adverse events. The figures are a record of reported events, not a causal comparison or a basis for medical advice.
12. What the Result Does, and Does Not, Mean
The record documents a randomized comparison of levofloxacin and placebo and reports primary arm summaries for percent change in BK virus copies at 3 months. Those summaries are 70.3 with standard deviation 42.5 for levofloxacin and 69.1 with standard deviation 39.5 for placebo. They describe the posted outcome data but do not provide a formal estimate of the between-arm difference or its precision.
The result does not establish the direction of viral change, because the percent-change sign convention is not reported. It also does not establish whether any difference between groups is compatible with a meaningful effect, because a primary confidence interval and p-value are not reported. Similar central values alone do not demonstrate equivalence, and the record provides no equivalence margin or equivalence analysis.
The registry's hypothesis links reduced BK virus in blood with impaired progression toward virus-induced kidney damage. However, the primary outcome reported is viral-copy change, not a direct measure of kidney damage. The registry record does not report a primary kidney-damage result or demonstrate that the viral endpoint predicts kidney outcomes in this trial. No conclusion about clinical benefit or harm follows from the posted primary summaries alone.
The secondary comparison is unadjusted and imprecise, and it cannot supply the missing primary inferential analysis. The record also does not explain the primary outcome counts, identify the analysis population, or describe missing-data handling. These gaps constrain the strength of any interpretation. The posted results are best treated as descriptive trial information whose statistical precision and analysis choices are incompletely documented, not as a definitive answer to the treatment question.
13. Why This Trial Matters Statistically
This study illustrates why a randomized design and a complete statistical report are both important. Random assignment and masking can support a fair comparison, but the design labels alone do not reveal how allocation was carried out, whether masking was maintained, or how outcomes were analyzed. The registry's limited methodological detail leaves important questions about implementation and analysis unanswered.
It also demonstrates the distinction between arm-level summaries and a treatment-effect estimate. A median and a standard deviation describe the outcome within each group, but do not by themselves quantify the uncertainty in the contrast between groups. A primary estimate with a confidence interval would communicate both the direction and precision of the comparison. The registry does not report that information for the primary endpoint.
The endpoint definition matters as much as the numerical summary. Percent change has a direction that depends on its convention, and that convention is not stated in the record. A biologic measurement can be relevant to a clinical hypothesis without being identical to a patient-important outcome. Keeping the measurement's meaning separate from the hypothesized downstream consequence prevents overinterpretation.
Finally, the planning illustration shows how strongly sample-size calculations can depend on the assumed effect. Its values are derived from the observed secondary effect under stated assumptions and are not evidence of the study's original design rationale. The original sample-size justification is not reported. This distinction helps prevent retrospective planning figures from being mistaken for evidence that the completed study had adequate power or that its observed result is precise.
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 primary outcome is reported as a median with a standard deviation, but the registry does not explain this choice or give further distributional information. It also does not define the sign convention for percent change. Both omissions complicate interpretation of the primary arm summaries, including the direction of viral change and the relationship between the reported median and its spread.
The registry does not report a primary between-arm estimate, confidence interval, or p-value. It lists no reported analyses, and the primary method, analysis population, and adjustment strategy are not described. As a result, the reported summaries cannot be placed in the context of a documented inferential analysis or checked against a stated analysis plan.
Outcome counts in the primary results are 20 for levofloxacin and 19 for placebo, compared with total enrollment of 43. The record does not explain this difference or state whether missing observations, exclusions, or other analysis choices account for it. No missing-data method or sensitivity analysis is reported. The absence of these details limits assessment of potential bias from incomplete follow-up.
The single secondary comparison is unadjusted and has a broad confidence interval. The registry does not report a multiplicity plan, so the confirmatory status of that result is unclear. The planning illustration uses the observed secondary effect and stated assumptions; it does not provide the original sample-size rationale. Safety listings are also limited: event attribution, timing, and the denominator for the listed serious-event percentages are not reported in the registry record.
These limitations are specific to what the registry reports and does not report. They do not establish that the trial was conducted improperly, but they prevent a complete appraisal of the analysis and the precision of its primary treatment comparison.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: BK Treatment Study — NCT01034176.
- Registry record last updated 2017-04-24; status last verified 2017-03.
- Results first posted 2017-03-06.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
The BK Treatment Study is a completed phase 4 randomized, quadruple-masked, parallel-group trial sponsored by Brigham and Women's Hospital. It enrolled 43 participants and compared levofloxacin 500 mg every day for 30 days, with dose adjustment for renal function, against placebo taken daily for 30 days. The registry describes the study as multicenter.
The primary outcome was percent change in BK virus copies from baseline to 3 months. The reported medians were 70.3 for levofloxacin and 69.1 for placebo, with standard deviations of 42.5 and 39.5. A primary comparison estimate and its uncertainty are not reported. One secondary outcome and an unadjusted comparison are posted. The registry does not report the primary analysis method, analysis population, missing-data handling, multiplicity plan, or original sample-size justification.