Renal Salt Handling in Postural Tachycardia Syndrome Following Dietary Dopa Administration: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Renal Salt Handling in Postural Tachycardia Syndrome Following Dietary Dopa Administration (NCT01064739), a na early/phase 1 study. The primary outcome is Plasma Dopa 1 hr After Breakfast.

2. Clinical Question

The study's broader aims were to characterize the effects of dietary catecholamine sources in healthy individuals. These included measuring plasma and urinary catecholamines, investigating whether fava beans could induce natriuresis in a short-term study, and gathering preliminary information on heart rate and blood pressure. Those aims provide the physiological context, but they do not substitute for reported outcome values.

The title refers to postural tachycardia syndrome, while the registry's condition field identifies healthy participants. The record therefore describes a dietary study in healthy people, not a direct comparison of treatment groups or a trial in a population identified as having that syndrome.

3. Trial Design

This was an early-phase study with a single-group, longitudinal design. The registry lists allocation as not applicable and masking as none. Participants served as their own controls: the study compared measurements from a fixed-sodium diet period with measurements after fava beans were added. This design differs from a randomized parallel-group trial, in which separate groups are assigned different interventions.

Participants followed a methylxanthine-free diet providing 150 mEq sodium and 75 mEq potassium per day. They consumed the standard fixed-sodium diet for at least two days before the study and on study day one during an inpatient stay at the Vanderbilt Clinical Research Center. On study day two, participants ate 100 g of puréed fava beans and pods with the study diet at breakfast and lunch. The description specifies breakfast at 0800hr and lunch at 1200hr.

Blood was sampled before breakfast and at 1, 2, 4 and 6 hours after breakfast for catechol assays. The primary outcome was plasma dopa at one hour after breakfast. The record also describes measurements of other catechols and other time points. The registry lists 26 outcome measures and 0 analyses.

The fixed order is important for interpretation: the record describes the fixed-sodium period first and the fava-bean period second, rather than randomized treatment order. With a within-participant design, each participant's measurements can be compared across periods, but a change between periods cannot automatically be attributed only to the dietary addition. The registry record does not report a statistical plan addressing order or period effects.

The study is listed as completed. Its start is recorded as 2007-01 and primary completion as 2012-09. The sponsor is Vanderbilt University. Further details about the protocol or the reasons for its design are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Fixed Sodium Study Diet

Fixed Sodium Diet + Fava Beans

Reasons for not completing this period:

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Plasma Dopa 1 hr After Breakfast, measured over Plasma samples collected 1 hour after breakfast on both study days..

The primary endpoint is plasma dopa one hour after breakfast, measured in pg/mL and specified as a mean with standard deviation. Blood samples were collected at this time point on both study days. The recorded comparison therefore concerns a continuous laboratory measurement across the fixed-sodium diet period and the fava-bean period.

Dopa is relevant to the study's stated interest in dietary catecholamine sources. The study description explains that dopamine is present in the brain and kidneys and is involved in regulation of the body's salts. It also states that fava beans contain a substance that increases dopamine production by the kidneys. Measuring plasma dopa provides a biochemical measure aligned with the aim of characterizing catecholamine levels after dietary dopa exposure.

That endpoint should be distinguished from urinary sodium excretion, which is central to the study's stated hypothesis about natriuresis. Plasma dopa measures a circulating catecholamine; it does not directly measure sodium excretion, blood pressure, or heart rate. The registry record specifies plasma dopa at one hour as primary, while describing other catechols and time points as non-primary outcomes.

The endpoint's measurement and timing are described, but its observed mean and standard deviation are not reported in the registry record. Without those results, the direction, size, and precision of any difference between study days cannot be assessed from this record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a within-participant comparison mean?

General: in a within-participant design, measurements from the same person under different conditions are compared. Each participant can act as their own control, which can reduce the influence of characteristics that remain stable within that person. This design is not the same as a randomized comparison between separate groups. Here, the registry describes a fixed-sodium diet period followed by a period when fava beans were included. The order was therefore not randomized, and period or order effects cannot be ruled out from the design description alone.

What does the primary endpoint summarize?

The endpoint is a continuous measure: plasma dopa one hour after breakfast. The registry specifies a mean and standard deviation. General: the mean represents an average measurement, and the standard deviation describes the spread of participant measurements around that average. A mean difference between periods would describe the average change, but no such numerical difference or endpoint summary is reported in the registry record.

How would uncertainty be described?

General: an estimate such as a mean difference is subject to sampling variability. A confidence interval communicates uncertainty by giving a range of values compatible with the observed data under the analysis assumptions. A narrow interval indicates greater precision than a wide interval, but neither a confidence interval nor another measure of precision for the primary endpoint is reported in the registry record. A p-value, if available, would address compatibility with a specified null hypothesis under an analysis model; it would not by itself describe the size or practical importance of a difference. No primary-outcome p-value is reported in the registry record.

Why do order and timing matter?

General: measurements made at different times can reflect changes over time as well as changes associated with the intervention. When all participants follow the same sequence, effects of sequence, time, or other period-specific conditions can be difficult to distinguish from an intervention effect. The registry states that the fixed-sodium diet came first and fava beans were added on study day two. It does not report randomized order or a statistical adjustment for period effects. Blood sampling at the specified hours after breakfast helps define when the biochemical measurements were taken, but timing alone does not remove possible order effects.

What does over-dispersion mean in general?

General: over-dispersion occurs when variability in data is greater than a statistical model assumes. It is especially relevant to count outcomes when a simple model expects less variability than the observations contain; ignoring it can make uncertainty appear smaller than it is. The primary endpoint is a continuous plasma measurement, not a count. The registry record does not describe an analysis model or report a dispersion assessment, so no claim about over-dispersion in this study is warranted.

How should planning illustrations be read?

General: sample-size calculations are planning tools, not observed outcomes or proof that a study was adequately powered. The registry's stated planning assumptions describe an illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the target effect is expressed as a fraction of the observed effect. Such an illustration does not describe the actual single-group, self-controlled design, which was not a randomized two-arm comparison. Any sample-size figures from that approach should therefore be treated as planning illustrations rather than as evidence about the study's observed precision. The registry record does not report the study's own sample-size justification.

The registry record lists 0 analyses. It does not report the statistical model, handling of paired observations, assumptions about the distribution of plasma dopa, method for estimating uncertainty, or adjustments for multiple outcomes. Those details are needed to assess the appropriateness of a particular statistical analysis. They cannot be inferred from the endpoint definition or the study design description.

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("Fava Beans", "Fixed Sodium Study Diet")
n   <- c(13, 13)
m   <- c(11670, 1705)
sp  <- c(5440, 530)
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  Fava Beans  13  11670.000  5440.000  8382.641  14957.359
CARM  Fixed Sodium Study Diet  13  1705.000  530.000  1384.724  2025.276

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 26 outcome measures, including multiple catechol measurements and time points. Plasma dopa one hour after breakfast is identified as the primary outcome. The description calls other catechols and other time points non-primary outcomes, and the secondary-outcome list includes several entries for plasma norepinephrine. Because many outcomes or time points can be examined, a study may face a multiplicity issue: the more comparisons considered, the greater the chance that at least one appears noteworthy by chance alone. General statistical practice may address this with a prespecified hierarchy or adjustment, but such an approach is not reported in the registry record.

The record lists 0 analyses and does not provide outcome values, analysis populations, or a missing-data description. It therefore does not state whether all enrolled participants contributed to the primary endpoint, whether any measurements were unavailable, or how missing measurements were handled. The registry record does not report an intention-to-treat, per-protocol, or other analysis-population definition.

The endpoint description gives the sampling schedule and identifies plasma dopa at one hour after breakfast as primary. It does not state how observations were analyzed across periods, whether the comparison was paired, or how multiple outcome measurements were addressed. These omissions limit assessment of the reported analysis; they do not establish that a particular method was or was not used outside the registry record.

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 5% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists serious adverse events as 0 affected participants in the Fava Beans group and 0 in the Fixed Sodium Study Diet group. The listed number at risk is 14 for each group. No serious adverse-event terms are listed. Death counts are null, so deaths are not reported in the registry record.

For other, non-serious adverse events, the record lists 1 affected participant in the Fava Beans group and 0 in the Fixed Sodium Study Diet group. The listed number at risk is 14 for each group. These are registry entries, not a complete description of event type, timing, severity, or relationship to the dietary condition. The specific non-serious event is not identified in the record.

These counts should be read descriptively. The design was a single-group, sequential study in which participants served as their own controls, not a randomized, like-for-like comparison between independent groups. The entries therefore do not establish that the dietary conditions caused or prevented an event. Nor do zero listed serious events establish that an intervention is free of serious risks; the record reports only the listed observations from this study.

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

The record documents a short-term dietary study in healthy participants, with a fixed-sodium diet period followed by a period that included fava beans. The primary biochemical question concerned plasma dopa one hour after breakfast. The study description also gives context about urinary sodium, other catechols, heart rate, and blood pressure, but numerical outcome results for these questions are not reported in the registry record.

What can be concluded from the record is limited to the stated design, measures, and listed adverse-event figures. The primary endpoint's mean, standard deviation, and comparison are not reported. The record therefore does not show whether plasma dopa increased, decreased, or remained similar across periods, or how uncertain an estimated difference would be. The same limitation applies to the stated aims involving urinary sodium and cardiovascular measures.

General: a study's ability to detect or estimate an effect depends on more than the number enrolled. Variability, completeness of measurements, design, and analysis all matter. The enrollment of 14 does not itself demonstrate either that a difference was absent or that the study could estimate one precisely. The registry record does not report a sample-size justification or detailed analysis plan.

The study population also matters. The condition field identifies healthy participants, even though postural tachycardia syndrome appears in the title. Findings from a healthy-participant study, if numerical results were available, would not automatically answer a clinical question about people with that condition. The record does not describe a patient population with postural tachycardia syndrome.

Overall, the registry entry can be used to understand what was studied and how the dietary periods were arranged. It cannot support a claim about the magnitude or clinical importance of an effect, nor a conclusion that fava beans do or do not change sodium handling or blood pressure. Those interpretations require outcome results and their uncertainty.

14. Why This Trial Matters Statistically

This study is statistically notable for using a within-participant sequence to examine a dietary exposure. In such a design, measurements from the same person can be compared across conditions, which is conceptually different from comparing independent randomized groups. That distinction matters when interpreting any calculated contrast: the design and analysis must correspond to the way observations were collected.

The registry also illustrates why endpoint definitions should be kept distinct from a study's broader rationale. Plasma dopa at one hour after breakfast is the stated primary outcome. Urinary sodium excretion is central to the described hypothesis, and other aims concern catecholamines, heart rate, and blood pressure. These are related scientific questions, but they are not interchangeable measurements. A plasma marker alone cannot quantify urinary sodium excretion.

Multiplicity is relevant because the record lists 26 outcome measures and measurements at several times. A prespecified primary endpoint can help distinguish the main question from exploratory outcomes, but the registry record does not report how multiple analyses were handled. The absence of an analysis description makes it difficult to evaluate the inferential context of any findings.

Finally, a completed study record without numerical outcome results leaves a clear boundary between design information and evidence about effects. The record can inform readers about population, timing, diet, and endpoint selection. It cannot show the size or precision of an outcome contrast. This distinction is useful in clinical research: a well-described question and measurement plan are not substitutes for analyzable results.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry record identifies healthy participants, despite the mention of postural tachycardia syndrome in the title. This limits how directly the study's stated dietary questions can be related to people with that condition. The enrolled population is not described as having postural tachycardia syndrome.

The study used a fixed sequence: participants followed the standard fixed-sodium diet first and consumed fava beans with the study diet on study day two. Participants served as their own controls, but the record does not describe randomized order. As a result, a difference across periods could not be separated from order or time effects on the basis of the design description alone.

The primary outcome is a plasma catechol measurement, not direct urinary sodium excretion. Although the study description emphasizes sodium handling and mentions heart rate and blood pressure, numerical results for these outcomes are not reported in the registry record. The primary endpoint's mean and standard deviation are also not reported, preventing assessment of effect size and precision.

The registry lists 26 outcome measures but does not report a multiplicity strategy, detailed statistical methods, missing-data handling, or analysis populations. It also lists 0 analyses. The record does not report the study's sample-size justification or explain how the analysis addressed the within-participant structure. These gaps restrict statistical assessment of the findings.

The adverse-event entries are limited to counts. The non-serious event is not identified, deaths are not reported in the registry record, and the record does not provide further event details. These entries are not enough to characterize the full safety experience.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Renal Salt Handling in Postural Tachycardia Syndrome Following Dietary Dopa Administration — NCT01064739.
• Registry record last updated 2016-05-26; status last verified 2013-08.
• Results first posted 2013-07-31.
• 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 record describes a completed, early-phase, single-group study sponsored by Vanderbilt University. It lists 14 enrolled healthy participants and a longitudinal design in which participants served as their own controls. The dietary schedule compared a fixed-sodium diet period with a second study day that included fava beans.

The primary endpoint was plasma dopa one hour after breakfast, measured in pg/mL and specified as a mean with standard deviation. The study description also discusses urinary sodium, other catechols, heart rate, and blood pressure. Numerical outcome results and detailed statistical analyses are not reported in the registry record.

The listed serious adverse-event counts are 0 for both dietary groups. The record lists 1 affected participant for other adverse events in the Fava Beans group and 0 in the Fixed Sodium Study Diet group. These entries should be interpreted descriptively, given the sequential, non-randomized design.