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 Calcium and Phosphorus Whole-Body Balance and Kinetics in Patients With Moderate Chronic Kidney Disease (NCT04019379), a randomized na study. The primary outcome is Fractional Calcium Absorption.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04019379 |
| Phase | NA |
| Condition | Phosphorus and Calcium Disorders, Chronic Kidney Disease Mineral and Bone Disorder, Chronic Kidney Diseases |
| Allocation | Randomized |
| Design model | Crossover |
| Masking | Double |
| Enrollment | 3 |
| Arms in the primary outcome | 2 |
| Lead sponsor | University of Minnesota |
| Results posted | Yes |
2. Clinical Question
Population
Patients with moderate chronic kidney disease. The registry record describes a pilot study and lists chronic kidney diseases and chronic kidney disease mineral and bone disorder among the conditions.
Intervention
A high-phosphorus diet, received as part of a crossover sequence. The registry record also identifies a low-phosphorus diet as the other intervention.
Comparator
The low-phosphorus diet. The two sequences were high phosphorus followed by low phosphorus, or low phosphorus followed by high phosphorus.
Primary question
What fractional calcium absorption was estimated under each diet, using kinetic modeling of serum and urine calcium-44 isotope measurements after oral and intravenous isotope administrations?
The main outcome is fractional calcium absorption, expressed as a fraction of 1.00. The posted results give a mean for each diet and a full range. The mean is 0.3 for the high-phosphorus diet and 0.42 for the low-phosphorus diet. The ranges are 0.22 to 0.45 and 0.22 to 0.8, respectively. These are descriptive results from a pilot study; the registry record does not report an inferential comparison of the diets.
The study’s stated aim was to develop a method for measuring whole-body calcium and phosphorus balance and modeling the kinetics of both ions in people with chronic kidney disease. It also lists serum intact fibroblast growth factor 23, intact parathyroid hormone, and 1,25-dihydroxyvitamin D as secondary outcomes. The primary result alone does not answer whether the diets produce a reliable difference in fractional absorption, nor does it describe the other listed outcomes.
3. Trial Design
This is a randomized, double-masked crossover study listed as phase not applicable. The registry identifies the University of Minnesota as sponsor and records the study status as completed. The recorded start date is 2020-08-31, and the primary completion date is 2020-10-28. Enrollment is listed as 3.
Participants were assigned to one of two sequences: high-phosphorus diet followed by low-phosphorus diet, or low-phosphorus diet followed by high-phosphorus diet. In a crossover design, treatment conditions are evaluated within a sequence in which participants receive the different interventions, rather than assigning every participant to only one condition. This can make within-participant comparisons relevant, but such comparisons require an analysis that accounts for the paired and ordered nature of the observations.
The primary outcome is fractional calcium absorption measured over 48 hours. The registry describes determining it by kinetic modeling of serum and urine calcium-44 isotope after oral and intravenous isotope administrations. The posted arm-level results list 3 observations for the high-phosphorus diet and 3 for the low-phosphorus diet. The record does not provide participant-level values, sequence-specific results, period-specific results, or a paired treatment estimate.
The record lists 7 outcome measures and 3 secondary outcomes by name. It reports 0 analyses. No statistical analysis plan, period or sequence analysis, washout details, or rationale for the enrollment target is reported in the registry record. The information available therefore establishes the broad design and measurement approach but does not describe all operational or analytical details needed to evaluate a crossover analysis fully.
4. Participant Flow and Accounting
The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.
Overall Study
| Stage | Sequence A | Sequence B |
|---|---|---|
| STARTED | 1 | 2 |
| COMPLETED | 1 | 2 |
| NOT COMPLETED | 0 | 0 |
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 | Sequence A | Sequence B | Total |
|---|---|---|---|---|
| Participants analysed | 1 | 2 | 3 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 0 | 1 | 1 |
| Age, Categorical: >=65 years | Participants | 1 | 1 | 2 |
| Age, Continuous | years | 71 (71 to 71) | 52 (34 to 69) | 58 (34 to 71) |
| Sex: Female, Male: Female | Participants | 1 | 1 | 2 |
| Sex: Female, Male: Male | Participants | 0 | 1 | 1 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 0 | 0 | 0 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 1 | 2 | 3 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Asian | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 1 | 0 | 1 |
| Race (NIH/OMB): White | Participants | 0 | 2 | 2 |
| Race (NIH/OMB): More than one race | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
| estimated glomerular filtration rate (eGFR) | mL/min/1.73m^2 | 40 (40 to 40) | 35 (29 to 41) | 37 (29 to 41) |
| body mass index (BMI) | kg/m^2 | 34.7 (34.7 to 34.7) | 20.5 (19.2 to 21.8) | 25.2 (19.2 to 34.7) |
| Serum phosphorus | mg/dL | 2.5 (2.5 to 2.5) | 2.7 (2.6 to 2.8) | 2.6 (2.5 to 2.8) |
| Serum intact fibroblast growth factor-23 (iFGF23) | pg/mL | 27.6 (27.6 to 27.6) | 78.3 (77.9 to 78.7) | 61.4 (27.6 to 78.7) |
| Serum 1,25-dihydroxyvitamin D3 (1,25D) | pg/mL | 46 (46 to 46) | 26 (21 to 30) | 32 (21 to 46) |
| Serum intact parathyroid hormone (iPTH) | pg/mL | 85.5 (85.5 to 85.5) | 154.7 (115.1 to 194.4) | 131.7 (85.5 to 194.4) |
6. Primary Endpoint
The registry lists the primary outcome as Fractional Calcium Absorption, measured over 48 hours.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Full Range |
| Unit | fraction of 1.00 |
| Endpoint classification | not reduced to a single comparison |
Fractional calcium absorption is the proportion of administered calcium estimated to be absorbed. The outcome is expressed as a fraction of 1.00, with a larger value representing a larger estimated absorbed fraction. This is a physiologic measurement rather than a direct measure of symptoms, kidney function, or a clinical event.
The registry describes estimating the outcome by kinetic modeling of serum and urine calcium-44 isotope measurements after oral and intravenous isotope administrations. In general, using isotope measurements and a kinetic model can help distinguish the movement and handling of a substance from measurements of its concentration at a single moment. The record specifies a 48-hour timeframe for this primary outcome.
This endpoint is relevant to the stated aim of developing a method for simultaneous whole-body calcium and phosphorus balance and kinetic modeling in chronic kidney disease. However, the registry result gives a mean and a full range for each diet, without individual measurements or an inferential treatment comparison. It therefore describes the posted estimates but does not show how stable they are across participants or establish the size and precision of a within-participant diet effect. The modeling procedures and assumptions are not reported in enough detail to assess them independently.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted mean fractional calcium absorption is 0.3 under the high-phosphorus diet and 0.42 under the low-phosphorus diet. The low-phosphorus diet has the larger reported mean. The registry gives full ranges of 0.22 to 0.45 for the high-phosphorus diet and 0.22 to 0.8 for the low-phosphorus diet. The ranges overlap, and the low-phosphorus range extends farther upward. These summaries describe the observations; they are not a formal test of a diet effect.
Each diet’s reported arm count is 3, and the study enrollment is listed as 3. The observations are therefore very limited in number. With such sparse data, a mean can be strongly influenced by individual values, while a range gives only the observed extremes and does not quantify uncertainty in the estimated mean or in a treatment contrast. The registry record does not provide a confidence interval for the treatment difference, a standard error, a p-value, or a paired analysis.
The crossover structure matters to interpretation. Participants were assigned to sequences that switch from one diet to the other. A suitable comparison would ordinarily account for the repeated measurements within a participant and for the order in which diets were received. The record does not report whether or how sequence, period, or carryover effects were assessed, and the arm-level summaries do not reveal the paired changes. It is consequently not possible to infer a crossover treatment effect from the two means alone.
The result should be read as a small pilot’s descriptive, model-derived estimates under two diet conditions. It does not establish the precision or reproducibility of the isotope kinetic method, and it does not establish a statistically supported difference between diets. Nor does this primary endpoint by itself address the listed hormone outcomes or clinical outcomes. The registry record’s stated purpose includes developing a measurement method, so feasibility and measurement development are central context for interpreting the posted values.
The record does not report an analysis plan or a statistical comparison. As a result, the absence of a reported p-value should not be read as evidence that the diets are equivalent, and the difference between the displayed means should not be treated as a confirmed effect. More information on individual and sequence-level observations, the model, and the planned analysis would be needed to judge uncertainty and the relevance of the estimates beyond this pilot.
9. Statistical Methods Explained
The registry reports a mean and full range for fractional calcium absorption in each diet condition. These summaries answer different descriptive questions. A mean indicates the average of the reported observations, while a full range gives the lowest and highest observed values. Neither, on its own, measures the uncertainty of an estimated treatment contrast.
What does the mean describe?
The posted means are 0.3 for the high-phosphorus diet and 0.42 for the low-phosphorus diet. They summarize the outcome values assigned to each diet in the registry results. Because this is a crossover study, the observations may be related within participants. The arm-level means do not show which values came from the same participant, which sequence those participants followed, or how much each participant’s outcome changed between diets. Without that information, the means cannot reconstruct a paired comparison.
What does the range tell us?
The reported full range is 0.22 to 0.45 for the high-phosphorus diet and 0.22 to 0.8 for the low-phosphorus diet. A range shows the spread between observed extremes, but it does not indicate how the values are distributed between those extremes. It is also sensitive to individual observations, particularly when the number of observations is small. The ranges are not confidence intervals: they do not express a model-based level of precision for a population mean or diet contrast.
Why does the crossover design matter?
In general, crossover studies compare conditions that participants receive in sequence. Because measurements from the same participant are often correlated, an analysis can use the within-participant comparison rather than treating all observations as unrelated. The order of treatments and the timing of measurements can also matter. A suitable analysis may need to consider treatment, period, and sequence, and assess whether effects from an earlier period could influence a later one. These are general crossover-design considerations; the registry record does not describe whether these factors were included in an analysis.
What does kinetic modeling contribute?
The primary outcome was determined by kinetic modeling of serum and urine calcium-44 isotope after oral and intravenous administrations. In general, a kinetic model uses measurements over time to represent movement through a system and estimate quantities that are not directly observed as a single measurement. The registry identifies the measurement sources and the 48-hour timeframe, but it does not report model equations, parameter assumptions, fitting procedures, diagnostics, or uncertainty estimates. The resulting means should therefore be understood as model-derived estimates, with the model details unavailable for independent assessment.
How should uncertainty be understood?
A confidence interval is a general statistical way to express uncertainty around an estimated quantity, such as a mean or a treatment contrast. It reflects both the observed data and the assumptions of the analysis. The posted result includes ranges but no confidence interval for the treatment contrast. The record also does not report a standard error, p-value, or other formal comparison. Thus, the apparent difference between the arm-level means is descriptive, not a reported inferential finding. The available data do not establish how precisely the diet contrast is estimated.
What do the planning assumptions mean?
The record’s sample-size assumptions describe planning illustrations based on the observed effect, not the trial’s own design and not observed power. The stated illustration uses a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation; its target effect is a stated fraction of the observed effect. Such calculations are hypothetical planning aids: they ask what sample size might be needed under the specified assumptions. They do not show the probability that this completed study detected an effect, and they do not establish that the assumptions are appropriate for a crossover design. The registry record does not report a sample-size justification for the trial.
Finally, the record reports 0 analyses. This means the posted registry information does not include a reported formal analysis of the primary outcome. It is not possible to determine from the record whether an unposted analysis was conducted or what its results might have been. Interpretations should therefore stay with the posted descriptive summaries and the stated limits of the available statistical information.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists 7 outcome measures, including the primary outcome and 3 named secondary outcomes: serum intact fibroblast growth factor 23, serum intact parathyroid hormone, and serum 1,25-dihydroxyvitamin D. It reports 0 analyses. A multiplicity strategy—such as specifying which outcomes are confirmatory or adjusting interpretation for multiple statistical tests—is not reported in the registry record. Since no formal tests are posted, the record does not show whether multiplicity was addressed in an analysis.
Missing-data methods are not reported in the registry record. The outcome summaries do not explain whether all scheduled measurements were obtained, whether any measurements were excluded, how incomplete isotope data were handled, or whether the kinetic model could not estimate an outcome for any participant. No participant-level accounting of missing or unusable measurements is included in the registry record recorded for this result.
The analysis population is also not described. The record does not state which participants or periods were included in the primary outcome summaries, whether analyses followed assigned sequence, or how deviations from the planned diets or measurement schedule were treated. These details are especially relevant to a crossover study because the available observations can depend on which periods were completed and whether paired measurements are available.
Accordingly, the posted summaries cannot establish how outcome selection, missing observations, or analysis-population choices affected the result. Those elements are not reported in the registry record and should not be inferred from the arm counts or the study status.
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 |
|---|---|---|---|
| High Phosphorus Diet | 0 | 3 | 0.0% |
| Low Phosphorus Diet | 0 | 3 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| High Phosphorus Diet | 0 of 3 |
| Low Phosphorus Diet | 0 of 3 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| High Phosphorus Diet | 0 of 3 |
| Low Phosphorus Diet | 0 of 3 |
For the high-phosphorus diet, the registry lists 3 participants at risk for serious adverse events and 0 affected; for the low-phosphorus diet, it lists 3 at risk and 0 affected. The record also lists 3 at risk for other adverse events in each diet condition and 0 affected in each. Deaths are recorded as 0 for both conditions. No serious adverse event terms are listed.
These are the safety figures recorded for the groups and conditions in the registry. They describe events reported in this record; they do not establish that no adverse events occurred outside the reporting scope or observation period. In a small pilot, zero recorded events provide limited information about the frequency of uncommon events. The registry record does not provide additional detail about event definitions, monitoring procedures, attribution, or the duration of safety follow-up. The figures should therefore be read as the posted counts, not as a broad conclusion about safety.
12. What the Result Does, and Does Not, Mean
The result provides descriptive estimates of fractional calcium absorption under high- and low-phosphorus diet conditions in a pilot study of patients with moderate chronic kidney disease. The posted mean is 0.3 for the high-phosphorus diet and 0.42 for the low-phosphorus diet. The full ranges are 0.22 to 0.45 and 0.22 to 0.8, respectively. The record also describes the isotope-based kinetic modeling approach used to derive the primary endpoint.
The result does not establish that the diets differ. The registry does not report a formal test, a treatment-effect estimate, or a confidence interval for the contrast. The arm-level summaries do not show participant-level pairing, and the crossover sequence information makes that pairing important for interpreting a treatment comparison. The observed means and ranges cannot substitute for an analysis that accounts for the design.
The result also does not demonstrate that the measurement method is validated or reproducible. The study’s stated aim was to develop a method for measuring whole-body calcium and phosphorus balance and modeling the kinetics of both ions. The posted outcome indicates that model-derived fractional absorption values were recorded, but methodological details and validation results are not reported in the registry record.
Nor does this primary endpoint answer questions about the secondary hormone outcomes or clinical outcomes. The record names three secondary measures but does not report their results in the registry record for this interpretation. The safety figures show no events recorded in the listed groups, but the small study and absent follow-up detail limit what can be concluded from those counts.
The appropriate takeaway is narrow: this completed pilot reports arm-level estimates and ranges for a model-derived physiologic endpoint under two diet conditions. It does not establish a definitive diet effect, its precision, or its clinical importance. The lack of a reported inferential analysis is a limit on interpretation, not evidence of no difference.
13. Why This Trial Matters Statistically
This study is statistically interesting because it combines a crossover design with a model-derived physiologic outcome. The design can support within-participant comparisons, while the endpoint depends on kinetic modeling of isotope measurements. Both features make it important to understand how observations are linked and how the model produces its estimates.
The registry describes the interventions and sequences and gives a mean and full range for each diet. It does not report participant-level paired data, a treatment contrast, or a formal analysis. Those omissions mean readers cannot assess how much of the difference between the displayed means reflects within-participant changes, variation between participants, treatment order, or measurement uncertainty. The limitation is not resolved by looking only at the two arm-level summaries.
The study’s stated purpose is methodological development: simultaneous whole-body calcium and phosphorus balance and full kinetic modeling of both ions in chronic kidney disease. In this context, a pilot can contribute by testing a measurement approach and documenting whether model-derived outcomes can be reported. To judge the method’s statistical performance, however, readers would need details about the model, its assumptions, its precision, and how well estimates can be reproduced. Those details are not reported in the registry record.
The record is also a reminder that a completed study can have descriptive results without a posted inferential analysis. A mean, range, and group count do not by themselves answer whether a treatment contrast is precise or robust. Clear reporting of analysis methods and uncertainty is especially useful when the data are sparse and the design involves repeated measurements.
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 most immediate limitation is the very small study size: enrollment is listed as 3, and each diet’s reported arm count is 3. With so few observations, individual values can have substantial influence on the summaries, and the range offers little basis for judging how estimates might vary in other participants. The record does not provide individual values to inspect.
The crossover design is described through two treatment sequences, but the posted outcome is presented only by diet. No paired changes, sequence-specific results, or period-specific results are reported. The record does not state whether period effects, sequence effects, or carryover were assessed, or whether the analysis accounted for repeated measurements. These details are important to the interpretation of a crossover comparison.
The primary outcome is model-derived, but information needed to evaluate the model is not reported in the registry record. This includes the model specification, fitting method, assumptions, diagnostic checks, and uncertainty around the estimates. The record does not provide a formal statistical comparison, confidence interval, or p-value. It also reports 0 analyses.
Further limitations include the absence of reported missing-data methods, analysis-population definitions, a sample-size justification, and a multiplicity strategy. The registry lists secondary outcomes but does not report their results in the registry record. The record does not provide details of diet implementation, adherence, or the timing between periods. These omissions limit assessment of both the design and the reliability of the posted estimates.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Calcium and Phosphorus Whole-Body Balance and Kinetics in Patients With Moderate Chronic Kidney Disease — NCT04019379.
- Registry record last updated 2024-09-19; status last verified 2024-05.
- Results first posted 2024-09-19.
- 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
NCT04019379 is a completed randomized, double-masked crossover pilot study sponsored by the University of Minnesota. It enrolled 3 participants with moderate chronic kidney disease and compared high- and low-phosphorus diet conditions in two sequences. The registry lists the study start as 2020-08-31 and primary completion as 2020-10-28.
The primary outcome is fractional calcium absorption over 48 hours, determined by kinetic modeling of serum and urine calcium-44 isotope after oral and intravenous isotope administrations. The reported means are 0.3 for the high-phosphorus diet and 0.42 for the low-phosphorus diet, with full ranges of 0.22 to 0.45 and 0.22 to 0.8. The registry record reports 0 analyses and does not provide an inferential comparison or a paired treatment estimate.
The stated aim was to develop a method for whole-body calcium and phosphorus balance and kinetic modeling in chronic kidney disease. Interpretation is limited by the sparse data, absent participant-level crossover results, and missing details about the model and statistical analysis.