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 Measurements of Body Iron Excretion of Healthy Adults (NCT00755105), a registered phase not stated study. The primary outcome is Rate of Iron Excretion..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00755105 |
| Phase | Phase not stated |
| Condition | Healthy |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 77 |
| Arms in the primary outcome | n/a |
| Lead sponsor | USDA Grand Forks Human Nutrition Research Center |
| Results posted | Yes |
2. Clinical Question
Population
Healthy adults who had previously received iron-55 isotope in studies of iron absorption. The primary outcome population is described as per protocol. Safety groups are identified as male subjects, menstruating women, and postmenopausal women who consumed the tracer.
Intervention
There is no assigned treatment intervention described. This is an observational study of people who had already received iron-55. The study uses retention of the isotope in blood to estimate body iron turnover and calculate iron excretion.
Comparator
No randomized comparator is reported. The registry does not describe the listed groups as like-for-like control arms; they are population categories rather than assigned treatment groups. Allocation is not stated.
Primary question
The primary question is the mean rate of iron excretion, measured in milligrams per day, among the per-protocol population. The registry specifies a 95% confidence interval and a 4-year timeframe, but does not report the mean estimate or its interval.
3. Trial Design
NCT00755105, titled “Measurements of Body Iron Excretion of Healthy Adults,” is recorded as a completed observational study sponsored by the USDA Grand Forks Human Nutrition Research Center. Enrollment is listed as 77. The registry gives a start date of 1998-09 and a primary completion date of 2005-12.
The study concerns healthy adults who had previously received iron-55 isotope in iron-absorption studies. According to the brief summary, investigators measured retention of the isotope in blood during a 3-year period to estimate body iron excretion. The primary outcome description says excretion was calculated as body Fe in milligrams multiplied by a turnover rate estimated from blood activity of Fe55. Its stated timeframe is 4 years. The record does not explain the difference between the 3-year period in the summary and the 4-year outcome timeframe.
This is not a randomized comparison. Allocation is not stated, and the record cautions that the groups are not a like-for-like control comparison. The primary outcome population is described as per protocol. The record lists one primary outcome measure and one analysis, but does not report the analysis method or its result.
The safety record separates participants into male subjects, menstruating women, and postmenopausal women who consumed the tracer. These categories do not establish treatment arms or a causal comparison. The registry record does not describe a control group, random assignment, or a protocol-based reason for the enrollment size. Details of the study protocol and the rationale for the 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.
Before assignment: All enrolled participants were included
Overall Study
| Stage | Male Subjects Having Consumed Iron-55 Tracer | Menstruating Women Having Consumed Iron-55 Tracer | Postmenopausal Women Having Consumed Iron-55 Tracer |
|---|---|---|---|
| STARTED | 38 | 30 | 9 |
| COMPLETED | 29 | 19 | 5 |
| NOT COMPLETED | 9 | 11 | 4 |
Reasons for not completing this period:
| Reason | Male Subjects Having Consumed Iron-55 Tracer | Menstruating Women Having Consumed Iron-55 Tracer | Postmenopausal Women Having Consumed Iron-55 Tracer |
|---|---|---|---|
| Withdrawal by Subject | 9 | 11 | 4 |
Analysis population for the primary outcome, as defined in the registry: Per protocol
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 | Male Subjects Having Consumed Iron-55 Tracer | Menstruating Women Having Consumed Iron-55 Tracer | Postmenopausal Women Having Consumed Iron-55 Tracer | Total |
|---|---|---|---|---|---|
| Participants analysed | 38 | 30 | 9 | 77 | |
| Age, Continuous | years | 43 (SD 8) | 40 (SD 5) | 50 (SD 5) | 43 (SD 7) |
| Sex: Female, Male: Female | Participants | 0 | 30 | 9 | 39 |
| Sex: Female, Male: Male | Participants | 38 | 0 | 0 | 38 |
6. Primary Endpoint
The registry lists the primary outcome as Rate of Iron Excretion., measured over 4 years.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | 95% Confidence Interval |
| Unit | milligrams per day |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is the rate of iron excretion, expressed in milligrams per day. The registry defines it as body Fe in milligrams multiplied by a turnover rate estimated from blood activity of Fe55. The outcome is a continuous measure, and its reported parameter is the mean. The stated analysis population is per protocol, with a 95% confidence interval and a 4-year timeframe.
As a general statistical matter, a continuous endpoint can describe the magnitude of a measurement across participants rather than classify each person into an event category. A mean provides a measure of the center of the observed values. A confidence interval communicates uncertainty about the estimated mean, conditional on the data and the statistical method used; it is not a range that contains every participant’s individual measurement.
The registry’s stated rationale for measuring isotope retention is to estimate body iron excretion. The endpoint therefore connects the measured blood isotope activity to a calculated rate. The actual mean and confidence interval are not reported in the registry record, so the magnitude and precision of the primary outcome cannot be assessed from this record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The record identifies a clearly defined type of primary outcome: a mean iron excretion rate in milligrams per day, calculated using body Fe and a turnover rate estimated from blood activity of Fe55. It also specifies a 95% confidence interval, a 4-year timeframe, and a per-protocol population. These details describe what was intended to be estimated, but the registry does not report the resulting mean or confidence interval. The numerical outcome and its precision are therefore not available in the registry record.
This absence limits interpretation. Without the estimate, it is not possible to characterize the observed rate from the registry record, assess how precise the estimate was, or determine whether the confidence interval was narrow or wide. There is also no reported comparison against a control group. Because the study is observational and the record states that allocation is not stated, the group labels should not be interpreted as randomized treatment arms or as evidence of a causal contrast.
The study’s stated context is measurement rather than a treatment comparison: participants had received iron-55 in earlier iron-absorption studies, and retention in blood was used to estimate iron excretion. The record does not establish that the safety categories were designed for comparisons of the primary endpoint. Nor does it report separate iron-excretion estimates for those categories.
The timeframe descriptions require care. The brief summary describes measuring retention during a 3-year period, while the primary outcome lists a 4-year timeframe. The registry record does not explain how those descriptions relate. They should be read as two distinct entries rather than reconciled by assumption.
The record’s enrollment figure is 77, but enrollment alone does not show how many participants contributed usable measurements to the per-protocol analysis. The analysis denominator and the handling of unavailable measurements are not reported in the registry record. Accordingly, the enrollment figure should not be treated as the analysis sample size.
Overall, the registry record documents the study purpose, endpoint definition, and broad population, but it does not provide the primary result needed to judge the observed rate or its uncertainty. No conclusion about the size or precision of the excretion estimate can be drawn from the registry record alone.
9. Statistical Methods Explained
What does a mean estimate describe?
The registry specifies a mean for a continuous outcome. In general, a mean summarizes the central level of measured values in the analysis population. It is distinct from the range of individual observations: participants may have values above or below the mean. A mean is most informative when interpreted alongside a measure of uncertainty and a clear account of which observations were included.
Here, the endpoint is a calculated rate rather than a direct count of an event. The registry describes the calculation as body Fe in milligrams multiplied by a turnover rate estimated from blood activity of Fe55. That definition identifies the ingredients of the endpoint, but it does not report the individual measurements, the calculation details beyond that description, or the resulting mean.
What does a 95% confidence interval convey?
In general, a confidence interval expresses uncertainty in an estimate under a specified statistical model and procedure. It is not a guarantee that a particular interval contains the true value, nor does it describe the spread of individual participant values. A narrower interval generally indicates greater precision for the estimated quantity, while a wider interval indicates more uncertainty. The interval’s interpretation depends on the design, the data, and the method used to calculate it.
The registry lists a 95% confidence interval for the primary endpoint, but the interval’s limits are not reported in the registry record. The method used to construct it is also not reported. It is therefore not possible to evaluate its width or independently assess the assumptions behind it.
Why does the analysis population matter?
The primary outcome population is described as per protocol. In general, a per-protocol analysis uses participants who meet the study’s specified protocol criteria, but the criteria and exclusions must be known to understand exactly who contributes. The registry record does not give those criteria, the number analyzed, or the reasons any enrolled participants may have been excluded. Enrollment and the per-protocol analysis population should therefore not be assumed to be identical.
Missing measurements can affect both the mean and its uncertainty, especially if the likelihood of a missing value is related to the measurement itself or to participant characteristics. General statistical practice distinguishes the amount of missing information from the method used to address it. Neither the extent of missing outcome data nor its handling is reported in the registry record. No particular missing-data approach can be inferred.
What can an observational design establish?
In general, an observational study measures or analyzes characteristics without assigning participants to treatment groups for a randomized comparison. It can describe measurements in the studied population, but comparisons between naturally occurring groups may reflect differences other than the category used to divide them. The registry explicitly states that this is not a randomized comparison and that the arms are not a like-for-like control comparison. Allocation is not stated.
In this study, the listed safety categories distinguish male subjects, menstruating women, and postmenopausal women who consumed iron-55. Those descriptions do not establish that the categories are comparable for estimating a causal effect. The registry does not report a randomized allocation, a control group, or a causal contrast for iron excretion. The primary endpoint is presented as a mean rate, not as a treatment effect between assigned groups.
What do the planning assumptions mean?
General sample-size planning uses assumptions about the effect to detect, the significance level, allocation, and the statistical approximation. The registry’s planning illustration is described as based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It describes effects as fractions of the observed effect. The stated convention is participants per arm for outcomes other than time-to-event outcomes; time-to-event planning tables give total events.
These are planning assumptions, not a description of the study’s actual observational design. In particular, equal allocation between two arms does not establish that participants were randomized or that the study had comparable arms. The registry does not report a sample-size justification for the study’s own design. A planning calculation based on an observed effect is not observed power, and it does not replace the reported outcome estimate and confidence interval.
What can be concluded from the listed analysis?
The record lists one analysis for one primary outcome, but does not provide the statistical procedure, numerical result, or confidence-interval limits. It does not report whether the analysis adjusted for participant characteristics or how the calculation treated variability in the measurements. Those omissions prevent independent evaluation of the analysis. General principles can explain what the specified mean and confidence interval are intended to represent, but they cannot fill in the absent result or method details.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists one primary outcome measure and one analysis. That listing does not provide a complete account of all analyses that may have been conducted, and the registry record does not report a multiplicity adjustment or a plan for controlling error across multiple tests. A specific multiplicity strategy should not be inferred from the number of listed outcomes alone. The statistical plan is not reported in the registry record.
The primary outcome population is identified as per protocol, but the eligibility rules for that analysis, the number of participants analyzed, and any exclusions are not reported. Enrollment is listed as 77; it should not be taken as the analysis denominator without a reported accounting of participants contributing endpoint data.
The record does not report the amount or pattern of missing outcome data, reasons measurements may have been unavailable, or the method used to handle missingness. It also does not describe imputation, sensitivity analyses, or whether all observed measurements were used. These details matter because incomplete measurement can influence both an estimated mean and its uncertainty. Without them, the completeness and robustness of the primary analysis cannot be assessed from the registry record.
Interim analyses, stopping rules, and a prespecified statistical analysis plan are not reported in the registry record. No conclusions about those procedures should be drawn from the completed status or the single listed analysis.
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 |
|---|---|---|---|
| Male Subjects Having Consumed Iron-55 Tracer | 0 | 29 | 0.0% |
| Menstruating Women Having Consumed Iron-55 Tracer | 0 | 19 | 0.0% |
| Postmenopausal Women Having Consumed Iron-55 Tracer | 0 | 5 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 1% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Male Subjects Having Consumed Iron-55 Tracer | 0 of 29 |
| Menstruating Women Having Consumed Iron-55 Tracer | 0 of 19 |
| Postmenopausal Women Having Consumed Iron-55 Tracer | 0 of 5 |
The registry reports separate safety groups for male subjects, menstruating women, and postmenopausal women who consumed iron-55. In these groups, serious adverse events are recorded as 0 for 29 at risk, 0 for 19 at risk, and 0 for 5 at risk, respectively. Other adverse events are also recorded as 0 for 29 at risk, 0 for 19 at risk, and 0 for 5 at risk, respectively.
These are descriptive counts within the listed groups, not randomized comparisons. The categories should not be interpreted as treatment arms, and the counts do not establish a causal difference or equivalence between groups. The death entries are null, so deaths are not reported in the registry record; null should not be interpreted as a reported count of zero. The registry does not list serious adverse-event terms. The record does not provide additional detail on adverse-event collection, observation duration for safety, or completeness of reporting, so those aspects are not reported in the registry record.
12. What the Result Does, and Does Not, Mean
The registry record establishes that the study was designed to estimate iron excretion in healthy adults who had previously received iron-55 in iron-absorption studies. It defines the primary outcome as a mean rate in milligrams per day and describes how the rate was calculated using body Fe and a turnover rate estimated from blood activity of Fe55. It also specifies a 95% confidence interval, a 4-year timeframe, and a per-protocol population.
What the record does not provide is the primary mean, its confidence-interval limits, or the statistical procedure used to obtain them. As a result, it does not show the magnitude or precision of the estimated rate. The absence of the result does not mean that no result was obtained; it means the result is not reported in the registry record.
The design also sets limits on interpretation. This is an observational study, not a randomized comparison. Allocation is not stated, and the record cautions that the groups are not a like-for-like control comparison. The listed sex and reproductive-status categories should not be treated as treatment assignments or as evidence of causal effects.
The registry describes isotope retention during a 3-year period in the brief summary, while the primary endpoint timeframe is 4 years. It does not explain the relationship between these descriptions. The analysis population is per protocol, but criteria, analysis counts, and handling of missing data are not reported.
The safety entries record zero serious and zero other adverse events in each listed group, while death values are not reported. These entries do not provide a comparison of treatments or establish broader safety conclusions. The record supports a description of the planned measurement and the recorded safety counts, but not conclusions about an unreported primary estimate or causal treatment effects.
13. Why This Trial Matters Statistically
This study is statistically distinctive because it focuses on estimating a continuous physiological rate from isotope retention rather than comparing assigned treatments. The registry describes a calculation that links body Fe to a turnover rate estimated from blood activity of Fe55. That makes clear why the endpoint depends on both the biological quantity and the measurement-based turnover estimate.
For a continuous endpoint, the mean and its uncertainty are central to interpretation. A confidence interval can help readers judge the precision of an estimate, but only when the estimate, interval, and method are reported. In this record, the primary mean and its 95% confidence interval are not reported. The outcome definition is therefore available, but the numerical evidence needed to evaluate the estimate is not.
The record also illustrates why study design and analysis populations matter. An observational study can describe measured rates in its participants, but it does not create randomized comparison groups. The record explicitly cautions against treating the groups as like-for-like controls. The per-protocol label further makes it important to know who contributed measurements, yet the analysis criteria and count are not reported.
Finally, the different timeframe descriptions and the absence of missing-data and analysis-method details constrain reproducibility. These limitations do not invalidate the study’s stated measurement objective, but they reduce what can be assessed from the registry record. For statistical readers, the key distinction is between a well-described endpoint and a reported, interpretable estimate: the former is present, while the latter is not reported in the registry record.
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 limitation for interpreting the registry record is that it does not report the primary outcome estimate or its confidence interval. The endpoint definition and requested measure are described, but the observed rate and its precision cannot be evaluated.
The design is observational, and allocation is not stated. The registry warns that the groups are not a like-for-like control comparison. The study therefore does not support interpreting the listed categories as randomized arms or as a causal contrast. The record also does not report a control group for the primary outcome.
The primary outcome is described as per protocol, but the analysis criteria, number analyzed, exclusions, and reasons for exclusion are not reported. Enrollment is listed as 77, but the registry does not establish that every enrolled participant contributed to the endpoint analysis. Missing measurements and their handling are also not reported.
The brief summary describes blood isotope retention during a 3-year period, whereas the primary outcome lists a 4-year timeframe. The record does not explain the difference. The statistical method for the mean and confidence interval, any adjustment for participant characteristics, and the analysis plan are not reported.
Safety reporting is limited to group counts. Death values are null and therefore not reported in the registry record; they cannot be read as zero deaths. The record does not provide further details on safety observation or completeness. The enrollment rationale, protocol-specific sample-size justification, and interim analysis procedures are also not reported in the registry record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Measurements of Body Iron Excretion of Healthy Adults — NCT00755105.
- Registry record last updated 2018-07-02; status last verified 2018-05.
- Results first posted 2009-04-09.
- 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.
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18. Record Summary
NCT00755105 is a completed observational study sponsored by the USDA Grand Forks Human Nutrition Research Center, with enrollment listed as 77. Its objective was to measure iron excretion in healthy adults who had previously received iron-55 in iron-absorption studies.
The primary endpoint is the mean iron excretion rate in milligrams per day, calculated from body Fe and a turnover rate estimated from blood activity of Fe55. The endpoint is specified for a per-protocol population with a 95% confidence interval and a 4-year timeframe. The brief summary separately describes isotope retention during a 3-year period.
The primary mean, confidence-interval limits, analysis method, analysis denominator, and missing-data handling are not reported in the registry record. The study is not a randomized comparison, and allocation is not stated. Safety entries report zero serious and other adverse events in the listed groups; death values are not reported.