HALT Progression of Polycystic Kidney Disease Study A: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for HALT Progression of Polycystic Kidney Disease Study A (NCT00283686), a randomized phase 3 study. The primary outcome is Study A: Percent Annual Change in Total Kidney Volume.

2. Clinical Question

The central statistical question is whether the two randomized treatment strategies were associated with different average annual percentage changes in total kidney volume among participants in Study A. The registry also reports a comparison between two blood-pressure target groups. These are separate comparisons within a factorial trial, rather than a single comparison of four unrelated regimens.

The treatment comparison is ACE-I + ARB versus ACE-I Alone. The blood-pressure comparison is Low Blood Pressure Group versus Standard Blood Pressure Group. Total kidney volume was assessed by abdominal MRI at baseline and at 2-, 4- and 5-year follow-up. The outcome is expressed as a percentage change per year, so the comparison concerns the rate of change in kidney volume, not simply a single final measurement.

The registry reports average group outcomes and mixed-model comparisons. These results describe the posted endpoint analyses; they do not, by themselves, establish how every participant’s kidney volume changed or explain the clinical importance of any difference.

3. Trial Design

HALT Progression of Polycystic Kidney Disease Study A is listed as a Phase 3, randomized, quadruple-masked, factorial study. The registry records enrollment of 558 and identifies the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) as sponsor. The study status is completed. Its recorded start is 2006-01 and its primary completion is 2014-06.

The factorial design combined two treatment dimensions: RAAS medication and blood-pressure target. Participants were assigned to lisinopril plus telmisartan or lisinopril plus placebo, together with either standard control at 120-130/70-80 mm Hg or low control at 95-110/60-75 mm Hg. This yields four described combinations. The posted primary results, however, are presented as marginal comparisons: ACE-I + ARB against ACE-I Alone, and Low Blood Pressure Group against Standard Blood Pressure Group.

The registry summary places Study A in early disease, defined as GFR >60 mL/min/1.73 m2. It distinguishes this study from a concurrent study of moderately advanced disease, but the present results concern Study A only. The summary says participants in Study A would be followed for at least 5 years; the primary endpoint timeframe lists baseline and 2-, 4- and 5-year follow-up.

The reported arm counts for the primary outcome are 271 for ACE-I + ARB, 282 for ACE-I Alone, 271 for the Low Blood Pressure Group and 282 for the Standard Blood Pressure Group. These are counts attached to the two marginal comparisons, not four independent sets of participants. The registry does not explain the relationship between the overall enrollment and the analysis counts. Randomization, masking and factorial allocation describe the design, but allocation procedures and details of how masking was maintained are not reported in the registry record.

The listed secondary outcomes include eGFR, albuminuria, aldosterone, left ventricular mass index, renal blood flow, all-cause hospitalizations and physical and mental quality-of-life summaries. The registry lists 9 outcome measures and 18 analyses.

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:

Analysis population for the primary outcome, as defined in the registry: Analyses were conducted on all participants who had at least one total kidney volume measurement using intention to treat.

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 Study A: Percent Annual Change in Total Kidney Volume, measured over Baseline and 2-, 4- and 5-year follow-up.

The primary endpoint is annual percentage change in total kidney volume, measured using abdominal magnetic resonance imaging at baseline and at 2-, 4- and 5-year follow-up. It describes the average rate of change in a structural measure over the follow-up period, rather than a single kidney-volume value at one visit. The registry identifies the endpoint as a mean and reports 95% confidence intervals for the group estimates.

Total kidney volume is used in this study as a measure of cystic disease progression. As a general statistical interpretation, a rate-based endpoint can make repeated measurements over time relevant to the comparison: it focuses attention on how the measure changes, rather than only on its value at the end. That does not mean the endpoint fully represents kidney function or every aspect of disease experience. The registry separately lists eGFR and other outcomes, reinforcing that kidney volume is one outcome among several considered.

The posted group means are 6.0 for ACE-I + ARB and 6.2 for ACE-I Alone, with respective 95% confidence intervals of 5.5 to 6.4 and 5.7 to 6.7. For blood-pressure groups, the means are 5.6 for Low Blood Pressure Group and 6.6 for Standard Blood Pressure Group, with respective 95% confidence intervals of 5.2 to 6.1 and 6.1 to 7.1. The unit is percentage of total kidney volume; the registry describes the endpoint as annual percentage change.

The population description says analyses used intention to treat and included all participants with at least one total kidney volume measurement. Further details about the construction of the annual change measure, handling of measurements at different visits, and treatment of missing follow-up measurements are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The endpoint is continuous: it is a numeric measure expressed as annual percentage change in total kidney volume. The registry reports group means and 95% confidence intervals. The randomized factorial design included two factors, medication assignment and blood-pressure target. In the posted primary analyses, results are grouped by each factor: ACE-I + ARB versus ACE-I Alone, and Low Blood Pressure Group versus Standard Blood Pressure Group.

What does a mean describe?

A mean is the arithmetic average of the observations in a group. As a general statistical explanation, it gives a compact summary of the group’s central level, but it does not show the full distribution of participant outcomes. Participants can have values that differ substantially from the mean. The registry does not report an additional measure of spread for the primary endpoint; the displayed uncertainty measure is a 95% confidence interval.

How should a confidence interval be read?

A confidence interval gives a range of values compatible with the estimate under the statistical method and assumptions used. In general, a 95% confidence interval reflects the long-run coverage property of the procedure, rather than a 95% probability that a particular fixed effect lies in the interval. It conveys precision as well as direction. The interval for the medication comparison is reported as -0.8 to 5.0, while its p-value is 0.52. The interval for the blood-pressure comparison is -1.6 to -0.2, with p = 0.006. Those are sponsor-reported comparison results, not newly calculated estimates.

Why use a mixed model?

The registry identifies the comparison method as Mixed Models Analysis. In general, mixed models can analyze repeated measurements while representing dependence among observations from the same participant; repeated observations are not ordinarily independent. These models can also accommodate variation in trajectories across participants. Those are general properties, not claims about the specific model used in this trial. The registry record does not report the model formula, covariance structure, fixed effects, random effects, assumptions, or exact approach used to obtain the annual change estimate.

The endpoint description refers to measurements at baseline and at 2-, 4- and 5-year follow-up. Repeated measurements can be informative about the course of an outcome over time, but the statistical treatment of incomplete sequences matters. The primary analysis population is described as all participants with at least one total kidney volume measurement, using intention to treat. The registry does not give enough detail to determine how the model handled missing measurements or whether additional assumptions or sensitivity analyses were used.

What does the factorial structure contribute?

In general, a factorial design evaluates more than one assigned factor within a shared trial structure. It can estimate the effects associated with each factor and may also allow assessment of whether the factors interact. Here, the registry posts two marginal comparisons, one for medication and one for blood-pressure target. It does not report an interaction estimate in the listed primary results. Therefore, these comparisons should not be read as evidence that the effect of one factor is identical at every level of the other factor.

As general context, a marginal comparison summarizes groups across the levels of the other factor, according to the analysis used. The trial’s actual model and averaging procedure are not described in detail in the registry record. The arm descriptions make clear that the medication regimens were paired with both blood-pressure targets, while the reported comparisons combine across those assignments.

What does the p-value add?

A p-value describes how incompatible the observed result is with a specified null hypothesis under the model and its assumptions. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. The reported p-values are 0.52 for the medication comparison and 0.006 for the blood-pressure comparison. Interpreting them requires the analysis assumptions and context, including whether and how multiple outcomes or comparisons were considered; those details are not reported in the registry record.

The record lists 9 outcome measures and 18 analyses. It does not provide a multiplicity adjustment or a complete prespecified statistical analysis plan. A significant result among multiple analyses can have a different interpretation from a single prespecified test, so the unreported multiplicity approach is relevant to how much weight to place on an isolated p-value.

What cannot be reconstructed?

The registry reports the summary estimates and mixed-model comparisons but does not report participant-level data, model diagnostics, a detailed missing-data strategy, or a sample-size justification. Those omissions prevent independent reproduction of the full model-based analysis from the posted summary statistics. The design-based sample-size assumptions listed with planning illustrations are not the trial’s observed power, and they do not establish what the trial was originally designed to detect.

10. Analyses Reported by the Sponsor

The registry’s own comparison results are the mixed-model analyses. For ACE-I + ARB versus ACE-I Alone, it reports a mean difference in final values of -0.2, a 95% confidence interval from -0.8 to 5.0 and p = 0.52. For Low Blood Pressure Group versus Standard Blood Pressure Group, it reports -1.0, a 95% confidence interval from -1.6 to -0.2 and p = 0.006. These values should be distinguished from the group means and their confidence intervals, which are separate summaries.

A recalculation from posted summary statistics, when available, is an unadjusted calculation and need not reproduce a model-based analysis using repeated measurements. In this record, no separate recalculated comparison estimate is reported among the registry entries for this analysis. The sponsor’s mixed-model results therefore remain the reported inferential analyses; the group means and their confidence intervals provide descriptive context but are not a substitute for that model.

The registry gives no full model specification, so the precise reasons a summary-statistic calculation might differ from a mixed-model estimate cannot be assessed. Any comparison between approaches would need to account for the repeated-measures structure, the analysis population and handling of incomplete follow-up. The stated results should be quoted as recorded rather than recomputed or treated as if they arose from a simple unadjusted two-group test.

11. Multiplicity, Missing Data and Analysis Populations

The primary population is described as intention to treat and includes all participants who had at least one total kidney volume measurement. This wording defines the stated analysis population, but it does not explain how participants with no post-baseline measurement were handled, whether every randomized participant contributed to the model, or how incomplete follow-up affected the endpoint estimate. The registry record does not report the extent or pattern of missing measurements, the assumptions used to address missing data, or sensitivity analyses for alternative assumptions.

The endpoint was assessed at baseline and at 2-, 4- and 5-year follow-up. For a repeated-measures outcome, missingness at one or more visits can influence the information available for estimating change. As a general statistical point, a mixed model may use available observations under particular assumptions about missingness, but the record does not report enough model or missing-data detail to say which assumptions applied. The phrase intention to treat does not, by itself, specify how missing outcome measurements were addressed.

The registry lists 9 outcome measures and 18 analyses, as well as two primary comparison results. It does not report a multiplicity adjustment, a testing hierarchy, a prespecified primary contrast within the factorial design, or the full statistical analysis plan. When many outcomes or comparisons are examined, the chance of at least one small p-value can increase; this is a general statistical concern, not a claim about what occurred in this trial. Without the planned approach, it is not possible to determine whether the posted p-values were adjusted or how the comparisons were prioritized.

The record also does not report a sample-size justification or the target effect used in trial planning. Enrollment is recorded as 558, while endpoint analyses have group counts of 271 and 282 for each of the two marginal comparisons. The registry does not reconcile those figures. These limitations mean the posted results can be interpreted as the reported analyses, but the basis for the analysis population, missing-data assumptions and control of multiplicity remains unclear.

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 serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: pregnancy, puerperium and perinatal conditions - other, specify (3.9%), renal and urinary disorders - other, specify (3.3%), surgical and medical procedures - other, specify (2.5%), abdominal pain (2.1%), hepatobiliary disorders - other, specify (1.8%).

The registry lists serious adverse event counts and the numbers at risk for each group. For ACE-I + ARB, 58 participants are listed as affected among 273 at risk; for ACE-I Alone, 90 are listed among 285 at risk. For the Low Blood Pressure Group, the corresponding figures are 69 among 274 at risk, and for the Standard Blood Pressure Group, 79 among 284 at risk. These are group-level counts, not a complete description of event timing, severity within each category, recurrence or causal attribution.

The registry also lists serious-event terms with percentages, including pregnancy, puerperium and perinatal conditions at 3.9%, renal and urinary disorders at 3.3%, surgical and medical procedures at 2.5%, and abdominal pain at 2.1%. Other listed terms are hepatobiliary disorders at 1.8% and neoplasms, including cysts and polyps, at 1.5%. The record does not explain the denominator for these term percentages in the registry record for this analysis, so they should not be interpreted as percentages of a particular randomized group.

Another adverse-event count is listed for each group, but its category definition is not reported in the registry record. Death counts are not reported in the posted data. These safety figures are descriptive; they do not establish that an event was caused by an assigned regimen or support a complete comparison of safety between groups.

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

The results describe average annual percentage changes in total kidney volume among the participants included in the registry’s endpoint analyses. For the medication comparison, the two posted group means are close, and the sponsor’s mixed-model result has p = 0.52 with an interval spanning zero. For blood-pressure target, the posted group means differ, and the sponsor’s mixed-model interval is -1.6 to -0.2 with p = 0.006. Those are statements about the recorded outcome and analyses, not conclusions about every outcome in the trial.

A statistical difference is not automatically a clinically important difference. The registry results do not provide a threshold for a meaningful change in annual kidney volume, nor do they connect these endpoint estimates to an individual participant’s prognosis. Likewise, a p-value is not a measure of treatment benefit, and confidence intervals do not describe the range of responses among individuals.

The endpoint is total kidney volume, not kidney function itself. The registry lists eGFR, albuminuria and other secondary outcomes, but their results are not included in the information analyzed. The posted primary endpoint therefore cannot stand in for all aspects of disease progression, quality of life or safety. The serious adverse event counts and terms also require separate interpretation and do not establish causality.

The factorial design includes both medication and blood-pressure assignments, but the listed analyses do not report whether the effects of these factors interacted. The results cannot answer whether a medication comparison varies according to blood-pressure target. Missing-data methods, model details and multiplicity handling are also not reported in the registry record, limiting assessment of robustness.

Overall, the record supports a careful description of the reported means, confidence intervals and model-based comparisons. It does not justify a treatment recommendation, a claim that all participants experienced the average outcome, or a broad conclusion about the full balance of benefits and harms. The interpretation should remain tied to Study A, its stated analysis population and the total-kidney-volume endpoint.

14. Why This Trial Matters Statistically

This study raises several statistical issues that matter in clinical research. First, its factorial design evaluates two randomized dimensions within one trial: medication strategy and blood-pressure target. The posted comparisons are marginal comparisons for each dimension. Recognizing that structure prevents treating the four regimen combinations as if they were unrelated trials and highlights the importance of knowing whether interaction effects were planned and reported.

Second, the endpoint is measured repeatedly. Total kidney volume was assessed at baseline and at multiple follow-up visits, and the registry identifies a mixed-model analysis. Repeated observations from one participant are related, so analyses that ignore that dependence may not represent the data structure appropriately. The model details are not reported, making clear reporting of such methods important for appraisal and reproducibility.

Third, estimates should be read together with uncertainty. The two comparisons have different patterns in their reported intervals and p-values, but statistical evidence alone does not establish clinical importance. The interval and estimate help convey direction and precision; the p-value is not a measure of effect size. Keeping these roles distinct is central to sound interpretation.

Finally, the record illustrates why analysis populations, missing-data handling and multiplicity plans matter. The endpoint population is described as intention to treat with at least one measurement, but the exact missing-data approach is absent. The registry lists multiple outcomes and analyses without describing adjustment or a testing hierarchy. These reporting gaps do not erase the posted results, but they constrain how confidently readers can assess the full analysis strategy. Transparent plans and model descriptions would make it easier to evaluate whether reported estimates answer the intended questions.

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 the available Study A record. The primary outcome is described as annual percentage change measured across repeated MRI visits, but the exact calculation of that rate is not reported. The mixed-model analysis is named without a model formula, covariance structure, adjustment variables or diagnostic information. As a result, readers cannot reconstruct the sponsor’s inferential analysis from the posted summaries alone.

The stated analysis population includes participants with at least one total kidney volume measurement and is labeled intention to treat. The record does not explain the treatment of participants without a measurement, the amount or timing of missing follow-up data, or the assumptions and sensitivity analyses used for incomplete outcome data. The relationship between the overall enrollment of 558 and the reported endpoint group counts is also not explained.

The factorial allocation raises the possibility that the effect of one assigned factor could depend on the other. The listed results do not include an interaction estimate or describe how the marginal comparisons were constructed. The registry also does not report a multiplicity plan despite listing 9 outcome measures and 18 analyses. These omissions limit evaluation of the inferential context of the reported p-values.

The recorded medication-comparison confidence interval is -0.8 to 5.0 alongside an estimate of -0.2 and p = 0.52. Those values are quoted as recorded; the registry does not explain the interval’s construction. The posted summaries also do not give results for the listed secondary endpoints in the information analyzed. Safety data lack detail about the definition of the additional adverse-event count, the denominator for serious-event term percentages and deaths. Consequently, these results give a partial view of efficacy and safety rather than a complete account of the trial.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: HALT Progression of Polycystic Kidney Disease Study A — NCT00283686.
• Registry record last updated 2020-04-21; status last verified 2020-04.
• Results first posted 2015-02-27.
• 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

HALT Progression of Polycystic Kidney Disease Study A is a completed Phase 3 randomized, quadruple-masked factorial trial sponsored by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The registry records enrollment of 558 and describes Study A as enrolling participants with early disease, defined as GFR >60 mL/min/1.73 m2.

The primary outcome is annual percentage change in total kidney volume, measured by abdominal MRI at baseline and at 2-, 4- and 5-year follow-up. The posted results compare ACE-I + ARB with ACE-I Alone and Low Blood Pressure Group with Standard Blood Pressure Group. The mixed-model results are -0.2, 95% confidence interval -0.8 to 5.0, p = 0.52 for the medication comparison, and -1.0, 95% confidence interval -1.6 to -0.2, p = 0.006 for the blood-pressure comparison.

The registry lists multiple secondary outcomes and serious adverse event information. Detailed model specifications, missing-data methods, multiplicity handling and a complete statistical analysis plan are not reported in the registry record.