Red Cell Half Life Determination in Patients With and Without Sickle Cell Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Red Cell Half Life Determination in Patients With and Without Sickle Cell Disease (NCT04476277), a non-randomized early/phase 1 study. The primary outcome is Mean Red Blood Cells Lifespan in Participants.

2. Clinical Question

The study addresses a measurement question: whether red blood cell survival can be followed in people with differing sickle cell status using biotin-labeled cells. The registry background explains that some red blood cells in people with sickle cell disease die early, and the stated objective is to learn how long red blood cells live in people with and without the disease. The listed cohorts also distinguish participants with sickle cell disease before and after transplantation, as well as participants with sickle cell trait and healthy volunteers.

This is not a randomized trial asking whether one assigned treatment is better than another. Its central outcome is a duration measured within each cohort. The registry record does not report numerical mean lifespan results or a formal statistical comparison between cohorts, so the size and precision of any differences cannot be assessed from the record.

3. Trial Design

The study is listed as Early Phase 1, non-randomized, unmasked, and using a single-group model. It enrolled 22 participants and is marked completed. The registry dates are 2021-04-19 for study start and 2022-12-20 for primary completion. The record identifies the National Heart, Lung, and Blood Institute (NHLBI) as sponsor.

There are four described cohorts: Sickle Cell Disease Pre-Transplantation, Sickle Cell Disease Post-Transplantation, Sickle Cell Trait (HbAS), and HbAA (Healthy Volunteers). The primary outcome description concerns red blood cell survival in each of these groups. For the primary analysis, the stated population consists of participants who completed the study and had no exchange or simple red blood cell transfusions. The record does not provide further details on the number analyzed for the primary outcome in each cohort.

In the procedure described, a blood sample was collected, red blood cells were labeled with biotin in the laboratory, and the labeled cells were returned to the participant by vein injection. Subsequent blood samples were analyzed by flow cytometry to follow labeled cells until biotin was no longer detectable on red blood cells. The described participation period was up to 6 months.

Sampling schedules differed by cohort. For the Sickle Cell Disease Pre-Transplantation cohort, the listed schedule was baseline, twice weekly up to week 3, and then weekly up to week 22. For all other cohorts, it was baseline, weekly up to week 4, and then every other week up to week 22. The study was not masked, and no random allocation is reported. The registry record does not describe a randomized allocation process, a concurrent assigned control group, or a blinding procedure.

The record lists 14 outcome measures and 13 analyses. It names a set of secondary outcomes, including blood-cell counts and laboratory values, but does not give their numerical results in the registry record. The record also does not report the protocol or a detailed statistical analysis plan.

4. Participant Flow and Accounting

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

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Analysis includes participants that have completed study and had no exchange or simple red blood cell transfusions.

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 Mean Red Blood Cells Lifespan in Participants, measured over Sickle Cell Disease Pre-Transplantation cohort time frame is as follows: baseline, twice weekly up to week 3 then weekly up to week 22. All other cohorts, time frame is as follows: baseline, weekly up to week 4, then every other week up to week 22..

The primary endpoint is mean red blood cell lifespan, measured in days, for participants in the four named cohorts. The endpoint description says that peripheral blood samples were analyzed by flow cytometry until biotin was no longer detectable on red blood cells. The intent is to use the persistence of labeled cells as an indicator of how long those cells remain in circulation.

In general, a mean summarizes the average value in a defined group. A duration-based endpoint can describe the time course of a biological process, while the full range indicates the lowest and highest observed values reported for that group. The registry specifies the full range as its dispersion measure, but numerical mean values and ranges are not reported in the registry record. Consequently, the record does not show the level of variation among participants or the precision of each cohort’s mean.

The primary outcome is a measurement rather than a direct comparison of assigned treatments. The record names the cohorts and describes how lifespan was assessed, but it does not report a primary between-cohort contrast, an estimate of the difference between groups, or a confidence interval. The endpoint can therefore be understood as the study’s target measurement, but its numerical findings and comparative interpretation cannot be established from the registry record.

The stated analysis population excludes participants who had exchange or simple red blood cell transfusions and includes participants who completed the study. This definition is relevant because it identifies which participants were intended to contribute to the primary measure. The registry record does not specify how incomplete follow-up, early loss of detectable biotin, or other missing endpoint observations were handled.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical information reported in the registry is limited. It identifies a mean as the primary summary, gives the unit as days, and names the full range as the measure of dispersion. It does not report the numerical outcome estimates, confidence intervals, hypothesis tests, or a detailed statistical analysis plan. The methods below explain the general meaning of the listed choices and the implications of what is not reported; they do not presume analyses that the registry record does not describe.

What does a mean lifespan represent?

In general, a mean is the arithmetic average of measured values in a defined group. For this endpoint, the target quantity is the average number of days of red blood cell survival among the participants included in the analysis. A mean is one concise description of a group, but it does not show whether individual measurements cluster closely around that value or vary substantially. The registry’s stated full range would describe the span from the lowest to the highest observed value, but the endpoints of that range are not reported.

A mean and a range answer different descriptive questions. The mean indicates the central average, while the range reflects the extremes observed in the sample. A range can be sensitive to unusual observations and does not by itself characterize the distribution of all measurements. In general, readers often need additional information, such as the sample size analyzed and a suitable measure of uncertainty, to assess how stable a group mean may be. Those cohort-specific details are not reported in the registry record.

How does the measurement approach relate to the endpoint?

The registry describes labeling a participant’s red blood cells with biotin, returning those cells by vein injection, and collecting repeated blood samples. Flow cytometry was used to assess the labeled cells until biotin was no longer detectable on red blood cells. This repeated-observation approach provides the intended basis for estimating how long labeled cells persist. The registry gives different sampling schedules for the pre-transplantation cohort and the other cohorts, so the observation schedule was not identical across all groups.

In general, a duration outcome depends on how the event or endpoint is defined and how observation is conducted. Here, the record identifies the stopping condition as biotin no longer being detectable. It does not explain the statistical procedure used to convert the repeated measurements into a mean lifespan, how values at the detection limit were handled, or whether any model was used. Those methodological details are not reported in the registry record and should not be inferred from the outcome title alone.

What can cohort comparisons tell us?

The four groups represent participants with different disease, transplant, or trait status. Because allocation is non-randomized and the design is listed as single-group, the record does not support treating these groups as randomized treatment arms. In general, random allocation can help balance measured and unmeasured characteristics between assigned groups; without it, observed group differences may reflect differences in participant characteristics as well as differences associated with cohort status. This is a general design consideration, not evidence that any particular source of bias occurred in this study.

The registry does not identify a single planned contrast among the four cohorts, nor does it provide adjusted estimates or covariate information. It is therefore not possible to describe a registry-reported inferential comparison. Group-specific descriptive summaries could still be informative if reported, but their numerical values are absent from the registry record. No causal conclusion about transplantation or sickle cell status follows from the cohort labels alone.

What role does uncertainty play?

In general, a confidence interval expresses statistical uncertainty around an estimate under a specified method and assumptions. A narrow interval indicates more precision than a wide interval, although precision is not the same as freedom from bias. The registry record does not report confidence intervals for the primary outcome. It also does not provide a test statistic or p-value for a primary comparison. Without an estimate and an uncertainty measure, readers cannot tell how precisely the mean lifespan was determined.

The record describes planning illustrations based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is a stated fraction of the observed effect. Those are planning assumptions, not a description of the original trial design or evidence of achieved power. The registry does not report a sample-size justification for the study itself. Planning illustrations should not be read as observed power, and they cannot supply missing outcome estimates.

What does over-dispersion mean in general?

In general, over-dispersion occurs when the variability in observed data is greater than a statistical model assumes. If a model assumes too little variability, its uncertainty estimates may be too small and its inferential conclusions too confident. The registry record does not state that an over-dispersed model was used or that over-dispersion was assessed. This general concept is relevant only if a model for repeated or count-like observations is specified; no such model is described in the record.

What statistical plan is documented?

The record identifies the endpoint, unit, dispersion measure, cohorts, sampling schedules, and analysis population. It does not report a detailed analysis method, treatment of repeated measurements, handling of missing data, multiplicity adjustment, covariate adjustment, or interim analysis plan. These items are not reported in the registry record. Without them, the analysis should not be reconstructed by assumption. The most defensible reading is limited to the registry entries explicitly stated: a mean lifespan endpoint, a full-range dispersion measure, and a defined primary analysis population.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 14 outcome measures and 13 analyses, with mean red blood cell lifespan identified as the primary outcome. It also names secondary outcomes including antibody detection, white blood cell count, red blood cell count, hemoglobin, hematocrit, mean corpuscular volume, absolute reticulocyte count, and aspartate aminotransferase. Numerical results for these secondary outcomes are not reported in the registry record.

When a study examines several outcomes or several comparisons, the chance of at least one apparently noteworthy finding can increase. In general, multiplicity methods can address that issue by defining a testing hierarchy or adjusting inference across tests. The registry record does not report a multiplicity strategy, an outcome hierarchy beyond naming the primary measure, or a plan for managing multiple comparisons. It is therefore not possible to determine from the record whether or how multiplicity was handled.

The primary analysis population is described as participants who completed the study and had no exchange or simple red blood cell transfusions. The record does not provide the number analyzed in each cohort, reasons for non-completion, or a participant flow. It also does not state how missing measurements, incomplete sampling, or values at the point when biotin was no longer detectable were treated. Those methods are not reported in the registry record.

In general, missing data can affect both the size and representativeness of an analyzed sample. Complete-case analyses may be informative when completion is unrelated to the outcome after accounting for relevant factors, but that assumption cannot be evaluated without details about missingness and the analysis. No imputation method or sensitivity analysis is reported. It is also not reported whether the primary analysis population was specified before results were examined.

Accordingly, the published registry description allows readers to identify the stated analysis population and outcome list, but not to assess the consequences of missing data or multiplicity for the numerical findings. A protocol or detailed statistical analysis plan is not reported in the registry record.

11. 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.

The registry reports safety counts separately for the four cohorts. In Sickle Cell Disease Pre-Transplantation, zero serious adverse events, zero other adverse events, and zero deaths are listed among 6 participants at risk for each adverse-event category. In Sickle Cell Disease Post-Transplantation, the corresponding entries are zero, with 6 participants at risk. In Sickle Cell Trait (HbAS), the entries are zero, with 7 participants at risk. In HbAA (Healthy Volunteers), the entries are zero, with 3 participants at risk.

These figures describe what the registry record reports during the study; they do not establish that no event could occur or that the procedure has no risk. In general, a zero count in a small group means no event was recorded in that group during the reported observation, not that the underlying event probability is zero. The record does not report event terms, timing, duration of safety follow-up by participant, or additional detail about how events were collected. It lists no top serious adverse-event terms.

The number at risk is the denominator associated with the reported count, not an estimate of a population-wide rate. No rates or comparative safety tests are reported. The cohort counts should not be combined into a new overall figure, and differences in group size make direct comparisons especially limited. These registry entries should be interpreted as descriptive safety reporting rather than as evidence from a powered comparison.

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

The study is designed to measure red blood cell lifespan in participants with differing sickle cell status. It describes biotin labeling, repeat blood sampling, and flow cytometry as the measurement process. Its primary endpoint is mean lifespan in days, with the full range named as the dispersion measure. These details clarify the biological quantity the investigators sought to characterize and the general procedure used to follow labeled cells.

The registry record does not report numerical primary-outcome results. It therefore does not show the mean lifespan in any cohort, the observed ranges, or the precision of those estimates. It also does not report a numerical contrast between cohorts. No conclusion about the magnitude of an association between cohort status and lifespan can be drawn from the record’s methods and group descriptions alone.

The study does not use randomized allocation, and the listed groups are not established as like-for-like controls. In general, differences between non-randomized groups can reflect differences in who is included as well as differences related to the group-defining status. The record does not describe adjustment or matching that would address such differences. The pre-transplantation and post-transplantation labels also do not establish, by themselves, that results come from the same individuals measured at different times.

The record’s safety entries show zero serious adverse events, zero other adverse events, and zero deaths in each cohort’s reported risk set. These are descriptive counts from the registry and do not establish the absence of risk. The record does not give enough detail to infer event rates beyond the stated counts and participants at risk.

Overall, the record documents a measurement study and its intended endpoint, not a numerical demonstration of a particular lifespan or a treatment effect. It does not report a protocol-based sample-size justification, a detailed statistical plan, or the primary outcome estimates needed to judge precision. The findings should not be extended beyond what is actually recorded: a completed study with a stated method and analysis population, but without posted numerical lifespan results.

13. Why This Trial Matters Statistically

This study is statistically notable because its central task is measuring a biological duration across several participant groups rather than comparing randomized treatment assignments. Such a design puts emphasis on clear outcome definition, measurement schedules, analysis populations, and transparent reporting of uncertainty. The record states that labeled red blood cells were followed through repeated blood sampling and identifies mean lifespan as the primary endpoint.

The four cohorts distinguish sickle cell disease before transplantation, sickle cell disease after transplantation, sickle cell trait, and healthy volunteers with HbAA. That structure may allow lifespan to be described across clinically different groups, but the non-randomized, single-group classification matters. In general, cohort comparisons can be affected by differences between the people represented in each group. A statistical comparison does not by itself remove those differences, and the registry record does not report adjustment methods or a prespecified comparative estimand.

The different sampling schedules are also relevant to interpretation. The pre-transplantation cohort had more frequent sampling early in follow-up than the other cohorts, while later sampling schedules are described separately. In general, observation frequency can affect how finely a time course is characterized. The registry does not state whether the analysis accounted for differences in sampling schedules, so no such method should be assumed.

Transparent results would ordinarily let readers assess the mean, variability, and uncertainty for each group. Here, the registry record identifies a full range as the dispersion measure but does not report the numerical means or ranges. The absence of those estimates limits both descriptive interpretation and any comparative assessment. It also illustrates why a well-defined measurement method and complete numerical reporting are both important: the former explains what was intended, while the latter is needed to understand what was observed.

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.

A central limitation for interpretation is that numerical results for the primary endpoint are not reported in the registry record. The mean red blood cell lifespan and full range are named, but no cohort-specific values or uncertainty estimates are given. This prevents readers from evaluating the observed magnitude, variability, or precision of the measurement.

The study is non-randomized and described as a single-group model, despite having four cohorts. Cohort membership is not assigned at random, and the record does not report matching, adjustment, or a formal comparative analysis. Therefore, any apparent differences between groups would not automatically be attributable to the group-defining condition or transplantation status. The registry also does not clarify whether pre- and post-transplantation groups include the same participants or distinct participants.

The stated primary analysis population includes participants who completed the study and had no exchange or simple red blood cell transfusions. The record does not report how many participants in each cohort met this definition, how many did not complete the study, or why. It does not describe missing-data methods, the treatment of incomplete follow-up, or sensitivity analyses. These omissions make it difficult to assess the representativeness of the analyzed participants.

Sampling schedules differed between the pre-transplantation cohort and the other cohorts. The registry does not report whether this difference was incorporated into the analysis. It also does not state how the endpoint was estimated from repeated measurements or how the detection limit was handled statistically. A detailed statistical analysis plan, sample-size justification, and multiplicity strategy are not reported in the registry record.

Finally, safety reporting is limited to counts by cohort and risk set. No serious or other adverse events and no deaths are listed, but the record does not provide detailed event terms or follow-up information for safety. The cohort sizes are limited as reported, and absence of recorded events should not be interpreted as proof of no risk.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Red Cell Half Life Determination in Patients With and Without Sickle Cell Disease — NCT04476277.
• Registry record last updated 2024-02-13; status last verified 2023-02.
• Results first posted 2024-02-13.
• 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.

18. Record Summary

NCT04476277 is a completed Early Phase 1, non-randomized study with a single-group model and no masking. It enrolled 22 participants and was sponsored by the National Heart, Lung, and Blood Institute (NHLBI). The registry lists a study start of 2021-04-19 and primary completion of 2022-12-20.

The study examined red blood cell lifespan in four cohorts: sickle cell disease before transplantation, sickle cell disease after transplantation, sickle cell trait (HbAS), and healthy volunteers with HbAA. Biotin-labeled red blood cells were followed using repeated blood sampling and flow cytometry. The primary endpoint was mean red blood cell lifespan in days, with the full range specified as the dispersion measure.

The primary analysis population was participants who completed the study and had no exchange or simple red blood cell transfusions. Numerical primary-outcome estimates and a detailed statistical analysis plan are not reported in the registry record. The safety record lists zero serious adverse events, zero other adverse events, and zero deaths in each cohort’s reported risk set.