Acetazolamide and Spironolactone to Increase Natriuresis in Congestive Heart Failure: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Acetazolamide and Spironolactone to Increase Natriuresis in Congestive Heart Failure (NCT01973335), a randomized phase 4 study. The primary outcome is Acetazolamide Arm: Natriuresis 24 h.

2. Clinical Question

The study is described as a randomized, triple-masked, phase 4 trial with a factorial model. Its two objectives address different treatment contrasts: the acetazolamide regimen versus high-dose loop diuretics, and upfront spironolactone added to loop diuretic therapy. The posted primary result addresses the first contrast by pooling the corresponding arms across the spironolactone assignment. It should not be read as a standalone estimate of spironolactone's effect or as a clinical-outcome comparison.

3. Trial Design

The registry describes NCT01973335 as a phase 4 randomized trial using a factorial model and triple masking. The sponsor was Hasselt University. The record lists the study as starting in 2013-11, with primary completion in 2017-04, and status as completed. Enrollment was 34.

The four arm descriptions represent the combinations of two treatment factors: acetazolamide with low-dose loop diuretics versus high-dose loop diuretics, and upfront spironolactone versus no spironolactone. This arrangement allows the acetazolamide contrast to be considered across the spironolactone groups, and the spironolactone contrast across the loop-diuretic regimens. The registry does not report the allocation ratio or describe the specific procedures used to maintain masking.

For the primary endpoint, the posted arm summaries are: acetazolamide/low-dose loop diuretics with upfront spironolactone, n=8, mean 324.0 mmol and standard deviation 133.0; high-dose loop diuretics with upfront spironolactone, n=6, mean 300.0 mmol and standard deviation 165.0; acetazolamide/low-dose loop diuretics without spironolactone, n=9, mean 211.0 mmol and standard deviation 96.0; and high-dose loop diuretics without spironolactone, n=9, mean 190.0 mmol and standard deviation 91.0. These are arm-level summaries, while the reported primary analysis compares the two loop-diuretic strategies across both spironolactone groups.

The registry lists 21 outcome measures and 2 analyses. Secondary outcomes include NT-proBNP change after 72 h, renal-function outcomes, and hormone measures after 72 h. A protocol-level account of the analysis plan, including allocation procedures and any planned interim analyses, is 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.

Before assignment: None, every patient that was enrolled was immediately randomised and started with the protocol of the study.

Overall Study

Analysis population for the primary outcome, as defined in the registry: 2 patients not analysed because of errors with 24 h urinary collection

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 Acetazolamide Arm: Natriuresis 24 h, measured over 24h.

The primary endpoint is total natriuresis after 24 h, measured in mmol. According to the registry description, urine is collected for 24 h after the first administration of diuretics under the study protocol. Natriuresis is calculated as the total amount of urine in litres multiplied by urinary sodium concentration in mmol/L. The endpoint therefore combines urine volume and sodium concentration to quantify sodium excretion over the collection period.

This measure was used to compare the acetazolamide and low-dose loop-diuretic regimen with high-dose loop diuretics. In the stated comparison, the relevant groups include participants with and without upfront spironolactone. The endpoint is an early physiological measure of diuretic response; it is not itself a measure of survival, symptoms, hospital admission, or long-term kidney function. The registry lists some of those kinds of outcomes separately among secondary measures, but the primary endpoint is limited to the 24-hour urine collection.

In general, a continuous endpoint such as natriuresis retains information about the magnitude of each participant's measured response rather than reducing the result to a simple event count. Its interpretation depends on valid and sufficiently complete measurement. The registry specifically notes that 2 patients were not analysed because of errors with the 24-hour urinary collection. The record does not report further details about the collection errors or how they were handled beyond that statement.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: each participant's 24-hour natriuresis is measured in mmol. The registry reports the mean and standard deviation for each of the four factorial arms. The mean describes the average observed endpoint in an arm, while the standard deviation describes the spread of individual measurements around that arm's mean. In general, a standard deviation is not a confidence interval for the mean and does not indicate the precision of the treatment comparison by itself.

The sponsor reports a two-sided t-test and a mean difference based on final values. A t-test evaluates whether the observed difference in group means is inconsistent with a null hypothesis of no mean difference, under the test's assumptions. A two-sided test considers departures in either direction. The registry gives a mean difference of 30 mmol, a 95% confidence interval from -63 to 123, and p=0.515. The record does not give enough detail to identify any adjustment beyond the stated test or to describe additional model terms.

In general, a confidence interval communicates the uncertainty around an estimated effect under the analysis assumptions. Its endpoints mark values reasonably compatible with the data and model at the stated confidence level; it is not a guarantee that the true effect lies within the interval. Because this interval includes zero and spans negative and positive values, the result does not pin down a clear direction. The p-value is a measure of how unusual data at least as inconsistent with the null would be if the null and test assumptions held. It is not the probability that the null hypothesis is true.

The factorial structure matters for interpretation. There are two treatment factors: the loop-diuretic strategy and upfront spironolactone. The primary endpoint description says that the acetazolamide/low-dose loop-diuretic groups, with and without spironolactone, are compared with the high-dose loop-diuretic groups, also with and without spironolactone. Thus, the reported primary contrast addresses the loop-diuretic factor across the spironolactone arms. The arm-level means alone do not establish whether there is an interaction between the factors. An interaction analysis, or a distinct estimated spironolactone effect, is not reported in the registry record.

In general, over-dispersion means that observed variability is greater than a model expects. It can make standard errors too small if the model does not account for that extra variability. The registry reports standard deviations for the endpoint but does not report an over-dispersion assessment or a model designed to address it. Since the endpoint is continuous and the posted analysis is a t-test, the registry does not describe a count model or an over-dispersion adjustment.

The endpoint's measurement process is also relevant. Natriuresis is derived from urine volume and urinary sodium concentration over 24 h. In general, measurement errors in either component can affect the derived endpoint. The registry states that 2 patients were not analysed because of errors with the urine collection, but does not report the nature of those errors, the treatment groups involved, or whether the errors were related to participant characteristics or outcomes.

The registry record does not report a sample-size justification, a target power for the trial, an interim-analysis plan, or a detailed statistical analysis plan. It also does not report the prespecified significance level for the trial's sponsor analysis. The posted planning illustrations, if used, are based on the observed effect and assumptions stated for those illustrations; they are not observed power and do not establish the trial's original design rationale. Any specific protocol-level choices not described in the registry record should remain unknown.

For planning in general, calculations based on an observed effect are illustrations rather than guarantees of future performance. An observed effect can be imprecise, particularly when the trial is small, and the planning assumptions may not match a future study. The analysis record also does not provide enough information to assess model diagnostics, distributional assumptions, or sensitivity analyses. These omissions limit how fully the statistical methods can be independently evaluated.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Acetazolamide/Low-dose Loop Diuretics, Upfront Spi", "High-dose Loop Diuretics, Upfront Spironolactone", "Acetazolamide/Low-dose Loop Diuretics, no Spironol", "High-dose Loop Diuretics, no Spironolactone")
n   <- c(8, 6, 9, 9)
m   <- c(324, 300, 211, 190)
sp  <- c(133, 165, 96, 91)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Acetazolamide/Low-dose Loop Diuretics, Upfront Spi  8  324.000  133.000  212.809  435.191
CARM  High-dose Loop Diuretics, Upfront Spironolactone  6  300.000  165.000  126.843  473.157
CARM  Acetazolamide/Low-dose Loop Diuretics, no Spironol  9  211.000  96.000  137.208  284.792
CARM  High-dose Loop Diuretics, no Spironolactone  9  190.000  91.000  120.051  259.949

11. Analyses Reported by the Sponsor

The sponsor-reported analysis is a two-sided t-test of final values and gives a mean difference of 30 mmol, a 95% confidence interval from -63 to 123, and p=0.515. This is the primary numerical estimate reported for the acetazolamide comparison. The interval is compatible with effects in either direction, and the p-value does not provide evidence against the test's null at conventional levels.

No discrepancy is flagged between the sponsor analysis and a recalculated result in the registry information used for this analysis. The sponsor's reported analysis therefore remains the relevant result to interpret; there is no separate recalculated estimate to substitute for it. The registry does not provide sufficient detail to reconstruct a more adjusted analysis or to verify unreported modelling choices from the arm summaries alone.

The test compares the loop-diuretic strategies across the spironolactone groups, as described for the primary endpoint. It should not be mistaken for a reported test of the separate spironolactone objective. The registry record does not report a separate numerical primary estimate for that factor.

12. Multiplicity, Missing Data and Analysis Populations

The registry lists 21 outcome measures and 2 analyses, including a primary natriuresis endpoint and several secondary outcomes. The secondary outcomes include NT-proBNP change after 72 h, worsening renal function, persistent renal impairment, peak plasma aldosterone concentration after 72 h, and peak plasma renin activity after 72 h. Numerical results for these secondary outcomes are not reported in the registry record.

When a study assesses multiple outcomes or treatment contrasts, the chance of at least one apparently notable finding can increase. In general, multiplicity procedures can control that risk, but the registry does not report whether an adjustment was planned or used, how outcomes were prioritized beyond the stated primary endpoint, or whether the two study objectives were treated as a shared family of hypotheses. These details should not be inferred from the number of outcomes or analyses listed.

Missing-data information is limited. The primary endpoint description states that 2 patients were not analysed because of errors with 24-hour urinary collection. The registry does not report which arms these participants belonged to, whether the missingness was related to treatment or participant characteristics, or whether any imputation or sensitivity analysis was performed. The treatment of missing data for the other outcome measures is not reported in the registry record.

The primary comparison is described as including the acetazolamide groups with and without upfront spironolactone and the high-dose loop-diuretic groups with and without upfront spironolactone. The record does not provide a fuller analysis-population definition, such as details of adherence, protocol deviations, or exclusions beyond the urine-collection errors. It also does not report whether the analysis followed an intention-to-treat principle.

In general, multiplicity and missing-data choices affect how confidently estimates can be interpreted, particularly when several outcomes and treatment factors are examined. Without a reported analysis plan or fuller accounting of missingness, the primary result can be described as posted, but the broader inferential framework remains unclear.

13. 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 serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: hospital readmission due to heart failure (71.4%), serious hyperkalemia (0.0%).

The registry reports serious and other adverse-event counts by arm, with separate numbers at risk and affected, as well as deaths. For serious adverse events, the listed affected counts are 3 among 9 at risk in the acetazolamide/low-dose loop-diuretic arm with upfront spironolactone, 5 among 7 in the high-dose loop-diuretic arm with upfront spironolactone, 2 among 9 in the acetazolamide/low-dose loop-diuretic arm without spironolactone, and 3 among 9 in the high-dose loop-diuretic arm without spironolactone. The record also reports other adverse-event counts and deaths by arm.

The registry lists hospital readmission due to heart failure at 71.4% and serious hyperkalemia at 0.0% among its top serious-event terms. The record does not clarify in this information how those term percentages relate to the arm-level counts or provide further context for their denominators. They should therefore be read as registry-reported figures, not treated as directly comparable rates without that context.

Adverse-event counts are descriptive and do not, on their own, establish that an event was caused by a treatment. The registry information does not provide enough detail to compare safety formally, account for exposure time, or interpret deaths as treatment-related. Small arm-level counts also make simple comparisons especially uncertain.

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

The central result is an imprecise estimate of the difference in average 24-hour natriuresis between acetazolamide with low-dose loop diuretics and high-dose loop diuretics. The sponsor-reported mean difference is 30 mmol, with a 95% confidence interval from -63 to 123 and p=0.515. These statistics do not establish a clear direction or a precise magnitude of effect.

The result does not prove that the regimens are equivalent. Equivalence requires a prespecified margin and an analysis designed to determine whether the plausible difference falls within that margin; such a margin is not reported in the registry record. Nor does the result establish that one regimen is superior. The confidence interval includes values on both sides of no difference, and the p-value is not a measure of the probability that a treatment works.

The endpoint concerns sodium excretion over a 24-hour collection. It does not by itself answer questions about longer-term clinical outcomes, including survival, symptoms, or later hospital use. Secondary outcomes are listed in the registry, but their numerical results are not reported in the record. The separate stated objective about upfront spironolactone also lacks a numerical primary estimate in the record.

The arm means and standard deviations provide descriptive information for the four factorial groups, but they do not replace the reported primary contrast. The analysis combines across spironolactone groups for the acetazolamide question. Without a reported interaction assessment, the arm summaries should not be used to infer that the loop-diuretic contrast is the same or different under each spironolactone condition.

In general, a statistically non-significant result can reflect uncertainty as well as a small effect. The posted data support describing uncertainty in the 24-hour natriuresis contrast; they do not support a definitive claim about clinical benefit, equivalence, or a distinct spironolactone effect.

15. Why This Trial Matters Statistically

This trial is statistically informative as an example of how a factorial design can address more than one treatment factor within one study. The four arm combinations reflect the loop-diuretic strategy and the presence or absence of upfront spironolactone. The primary endpoint description focuses on the acetazolamide contrast across the spironolactone groups, while the study summary states a separate spironolactone objective. Distinguishing those questions is essential: a result for one factor should not be presented as an estimate for the other.

The endpoint also illustrates the difference between an early physiological measure and a clinical outcome. Natriuresis is calculated from a 24-hour urine collection and sodium concentration. It can describe the measured response during that period, but it is not itself evidence about longer-term outcomes. Keeping the outcome's time scale and meaning clear prevents a surrogate or intermediate measure from being overinterpreted.

The confidence interval is important alongside the p-value. The reported interval, -63 to 123 mmol, includes both negative and positive values, making the direction and size uncertain. A single p-value cannot convey that range of plausible estimates. The result also illustrates why a non-significant test should not be treated as proof of no difference.

Finally, the record highlights practical limits on interpretation: urine-collection errors led to exclusion from the primary endpoint analysis for 2 patients, and the registry does not describe the missingness in detail. A clear account of endpoint measurement, analysis populations, factorial contrasts, and uncertainty is crucial when judging what a small clinical trial can establish.

16. 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 comparison is based on a small trial, with arm-level endpoint counts of 8, 6, 9, and 9. The confidence interval is wide and includes values in both directions, so the estimate does not provide a precise account of the mean difference. The registry does not state a clinically important threshold for natriuresis, which further limits assessment of the practical meaning of the range.

The registry reports that 2 patients were not analysed because of errors with 24-hour urine collection. It does not identify the affected arms, explain the errors, or describe sensitivity analyses. As natriuresis depends on urine volume and sodium concentration, collection problems can affect the outcome measurement. The extent to which this exclusion might influence the result cannot be determined from the registry information.

The trial is factorial, but the posted numerical primary analysis addresses the acetazolamide comparison across spironolactone groups. A separate numerical estimate for the spironolactone objective and a test of interaction are not reported in the registry record. Arm-level means should not be treated as a substitute for those analyses.

The record lists secondary outcomes but does not report their numerical results in the information described. It also does not provide a detailed statistical analysis plan, sample-size justification, interim-analysis plan, or fuller analysis-population definition. The use of triple masking is recorded, but the registry does not specify who was masked or how masking was maintained.

Safety information is descriptive and lacks further details needed to assess event timing, exposure, attribution, or formal between-group comparisons. These limitations do not invalidate the posted result, but they restrict the range of conclusions that can be drawn from it.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: Acetazolamide and Spironolactone to Increase Natriuresis in Congestive Heart Failure — NCT01973335.
• Registry record last updated 2019-05-21; status last verified 2019-05.
• Results first posted 2019-03-21.
• 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.

20. Record Summary

NCT01973335 is a completed, randomized, triple-masked, phase 4 factorial trial sponsored by Hasselt University. It enrolled 34 participants and examined acetazolamide with low-dose loop diuretics versus high-dose loop diuretics, alongside an upfront spironolactone factor.

The primary endpoint was total natriuresis after 24 h, measured in mmol from a 24-hour urine collection. The sponsor-reported analysis was a two-sided t-test of final values, with a mean difference of 30 mmol, a 95% confidence interval from -63 to 123, and p=0.515. The interval is compatible with effects in either direction and does not give a precise estimate.

The registry notes that 2 patients were not analysed because of urine-collection errors. It lists secondary outcomes and adverse-event information, but a separate numerical primary estimate for the spironolactone objective is not reported in the registry record.