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 Diagnostic Performance of an Antigen Test for SARS-CoV-2 Infection (COVID-19) (NCT04610489), a na na study. The primary outcome is Proportion of True Positives.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04610489 |
| Phase | NA |
| Condition | Covid-19 |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 117 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Carilion Clinic |
| Results posted | Yes |
2. Clinical Question
Population
Outpatients with symptoms compatible with COVID-19. The registry describes a planned enrollment of 117 and identifies Covid-19 as the condition. It does not give further eligibility details or report the characteristics of participants who enrolled.
Intervention
The diagnostic test was the Quidel Sofia SARS Antigen Fluorescent Immunoassay, described as a direct antigen test performed on bilateral mid-turbinate swabs.
Comparator
The comparison was with rt-PCR testing using bilateral swabs. The brief summary describes the reference-standard test as a nasopharyngeal swab test, and the arm description names Quest SARS-CoV-2 rRT-PCR. The specimen collection methods therefore differed between tests.
Primary question
Among subjects who tested positive by rt-PCR, what proportion also tested positive by antigen? This is sensitivity relative to the rt-PCR result, as defined in the registry. The registry record does not report the observed proportion or its confidence interval.
3. Trial Design
This was a single-group diagnostic study, not a randomized comparison of treatments. The registry lists allocation as NA, masking as none, and the model as single group. Its study population description says subjects would undergo both the antigen test and rt-PCR testing. The record therefore describes a comparison of two diagnostic results within the study population, rather than separate intervention and control arms.
The antigen test was the Quidel Sofia SARS Antigen Fluorescent Immunoassay on bilateral mid-turbinate swabs. The reference test was rt-PCR; the brief summary specifies a nasopharyngeal swab, and the study-population description names Quest SARS-CoV-2 rRT-PCR and bilateral swabs. The difference in specimen collection is important when interpreting a comparison: the results reflect the testing approaches as described, including their specimen methods. The record does not establish how much any difference in results might be attributable to the assay versus specimen collection.
The registry lists enrollment of 117. The study start date was 2020-11-13, and the primary completion date was 2021-03-10. The status is terminated. A reason for termination, whether the planned enrollment was reached, and details about how enrollment and follow-up proceeded are not reported in the registry record. Phase is listed as NA. The sponsor is Carilion Clinic.
The primary endpoint was the proportion of rt-PCR-positive subjects who were antigen-positive, with a timeframe of 1 day. The record lists two outcome measures and 0 analyses. It does not describe a statistical analysis plan, the handling of indeterminate or missing test results, or an analysis population beyond the endpoint definition. The design details establish the question the study set out to address, but do not supply the numerical diagnostic results needed to answer it.
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 | Study Population |
|---|---|
| STARTED | 117 |
| COMPLETED | 117 |
| NOT COMPLETED | 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 | Study Population |
|---|---|---|
| Participants analysed | 117 | |
| Age, Customized: Age | Participants | 0 |
| Sex/Gender, Customized: Gender | Participants | 0 |
| Race and Ethnicity Not Collected | Participants | — |
| Region of Enrollment: United States | participants | 117 |
6. Primary Endpoint
The registry lists the primary outcome as Proportion of True Positives, measured over 1 day.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | 95% Confidence Interval |
| Unit | proportion of true positives |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is the proportion of subjects who were positive by rt-PCR and also positive by the antigen test. This is sensitivity relative to the specified reference standard: the denominator is the rt-PCR-positive group, and the numerator is the portion of that group that tests antigen-positive. A positive antigen result among a reference-positive subject is counted as a true positive under this endpoint definition.
Sensitivity is used to describe how often a test identifies cases that meet the reference definition. It is conditional on being reference-positive; it does not describe the chance that a person with a positive antigen result is truly infected, nor does it by itself describe performance among reference-negative subjects. Those are different questions and require other measures.
The registry gives a timeframe of 1 day, consistent with a comparison of test results rather than a long-term clinical outcome. It describes rt-PCR as the disease-positive reference and antigen as the test being assessed. Because the record describes mid-turbinate sampling for antigen and nasopharyngeal sampling for rt-PCR, the endpoint compares the reported testing procedures as a whole, not necessarily the assay technologies isolated from collection method.
The observed endpoint value, the number of rt-PCR-positive subjects, and the confidence interval are not reported in the registry record. Without those results, the endpoint definition can be explained, but the magnitude and precision of sensitivity cannot be assessed.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry identifies sensitivity as the primary outcome but does not report the observed proportion, its confidence interval, or the underlying positive-result counts. Consequently, the record does not establish a numerical estimate of how often antigen-positive results occurred among rt-PCR-positive subjects. It also does not allow an assessment of the precision of that estimate.
A sensitivity estimate is conditional on the reference result. It answers a narrower question than overall diagnostic performance: how often antigen testing is positive within the group classified as positive by rt-PCR. It does not, on its own, indicate how frequently an antigen-positive result corresponds to rt-PCR positivity. Nor does this endpoint describe the antigen test result distribution among rt-PCR-negative subjects. The registry record does not provide a reported specificity estimate or a complete diagnostic classification.
The choice of rt-PCR as the reference standard defines what counts as disease-positive for this endpoint. The brief summary calls it the reference standard, and the primary outcome description explicitly bases the denominator on rt-PCR-positive subjects. This makes the result an agreement-based measure relative to that test, rather than an independently verified measure of infection status. The record does not describe additional confirmation or adjudication procedures.
Specimen collection also matters to interpretation. The antigen test used mid-turbinate swabs, while the brief summary describes nasopharyngeal swabs for rt-PCR. A difference in results could reflect the combined testing procedures, including specimen collection, and cannot be assigned solely to the antigen assay from the registry description. The record does not report an analysis separating these components.
The registry status is terminated, but no reason is reported. This status alone does not explain whether recruitment, data collection, or analysis was completed as intended. Enrollment is listed as 117, but the record does not say how many had usable paired test results or were included in the primary endpoint analysis. The record lists 0 analyses, so no registry-reported analysis details can be used to clarify this.
In general, a confidence interval conveys uncertainty around an estimated quantity: a wider interval indicates less precision, while a narrower interval indicates greater precision under the method used. No interval for the primary endpoint is reported, so the precision cannot be described. There is also no basis in the registry record to characterize the result as strong, weak, favorable, or unfavorable. The registry entries describe the design and intended measure, not the observed diagnostic performance.
9. Statistical Methods Explained
The primary measure is sensitivity relative to rt-PCR. In general, sensitivity is the proportion of reference-positive cases that also receive a positive result from the test under evaluation. For this study, the registry defines reference-positive status by rt-PCR and the test-positive result by antigen testing. The measure is therefore conditional on the rt-PCR-positive group, rather than on all subjects enrolled.
What does the denominator represent?
The denominator for the stated endpoint consists of subjects classified as positive by rt-PCR. The numerator consists of the subjects in that group who were also positive by antigen. The registry describes the endpoint as the proportion of true positives and identifies it as sensitivity. It does not report either count or the resulting proportion. An endpoint definition should not be mistaken for an endpoint result: the intended calculation is specified, but its numerical output is absent from the registry record.
What does a confidence interval add?
In general, a confidence interval expresses the uncertainty associated with an estimate, based on the data and a specified statistical method. It helps readers distinguish an estimate that is precise from one that remains uncertain. Its interpretation depends on the calculation method and the data available, including the number of reference-positive observations. The primary endpoint lists a 95% confidence interval as its dispersion measure, but the interval itself is not reported in the registry record. There is therefore no interval width to interpret and no reported estimate around which to describe uncertainty.
Why does the reference test matter?
Diagnostic sensitivity depends on how reference-positive status is defined. Here, rt-PCR is identified as the reference standard, so the endpoint describes antigen positivity among rt-PCR-positive subjects. This is a comparison to the registry's stated reference, not proof that every reference result represents the underlying disease state without error. The record does not give information about an independent clinical adjudication process or other reference checks.
Why do the specimen methods matter?
The record describes antigen testing with mid-turbinate swabs and rt-PCR with nasopharyngeal swabs. In general, a diagnostic comparison can reflect both the tests and how specimens are collected. When collection methods differ, the comparison does not isolate the assay from specimen-related effects. This does not establish that specimen methods caused any difference; rather, it identifies a feature of the design that limits what could be attributed to the assay alone.
What can be inferred from the analysis information?
The registry lists two outcome measures and 0 analyses. This indicates that the record does not contain a listed analysis to interpret, but it does not establish what analyses may or may not have been conducted outside the registry record. The statistical analysis plan, any adjustments, and the treatment of incomplete, indeterminate, or discordant results are not reported in the registry record. No recalculated estimates are available in the registry record for this study.
How should sample-size planning be read?
In general, sample-size planning uses assumptions about the effect to be detected, the significance level, allocation, and the statistical method. A planning illustration is hypothetical: it describes what a future study might require under stated assumptions and does not show how many observations were analyzed or how precisely an observed result was estimated. The planning assumptions associated with this record describe a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and effects defined as fractions of an observed effect. Those assumptions are not the stated design of this single-group diagnostic study. The record does not report that they were used to plan this trial, and any planning illustration should not be interpreted as observed power or as evidence about the actual endpoint result.
Over-dispersion is a general statistical concern when variation in observed data exceeds what a chosen model assumes. In a count or clustered-data analysis, failing to account for over-dispersion can make uncertainty appear smaller than it is. The registry does not describe a model for the primary endpoint, an over-dispersion adjustment, or an analysis of clustered observations. Because no primary result or analysis method is reported, there is no basis to determine whether this issue was relevant to the actual analysis.
For a diagnostic proportion, the central interpretive questions are the estimated proportion, the size of the reference-positive group, the method used to calculate uncertainty, and how missing or indeterminate results were handled. The registry record does not report these analysis details or the numerical endpoint result. Accordingly, general statistical concepts can clarify what the intended endpoint means, but cannot fill in the missing trial-specific result.
10. Multiplicity, Missing Data and Analysis Populations
Multiplicity concerns arise when several outcomes, subgroup comparisons, or statistical tests are evaluated. In general, testing many hypotheses can increase the chance that at least one result appears notable by chance. Methods such as prespecifying a primary outcome or adjusting for multiple comparisons may address this, depending on the study aims and analysis plan. The registry lists two outcome measures, identifies the proportion of true positives as primary, and lists 0 analyses. A multiplicity strategy or a complete hierarchy of outcomes is not reported in the registry record, so it is not possible to assess how multiple outcomes were handled.
Missing-data handling is also not reported. The record does not state how subjects with absent, invalid, or indeterminate antigen or rt-PCR results were treated, whether repeat testing was allowed, or whether all enrolled subjects contributed to the primary endpoint. Enrollment is listed as 117, but the number included in the endpoint calculation is not reported. Enrollment should not be read as the denominator for sensitivity: that denominator is the rt-PCR-positive group, whose size is not given.
The registry identifies the study population and endpoint definition but does not specify a detailed analysis population, such as a rule for requiring interpretable results from both tests. The record also does not report a statistical analysis plan, sensitivity analyses for missing results, or procedures for handling discordant test outcomes. These omissions limit assessment of possible bias and reproducibility. They do not establish that data were missing or that a particular method was used; the relevant details are simply not reported in the registry record.
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 |
|---|---|---|---|
| Study Population | 0 | 117 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Study Population | 0 of 117 |
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 |
|---|---|
| Study Population | 0 of 117 |
The registry reports adverse-event figures for the study population. It lists 117 subjects at risk for serious adverse events and 0 affected, and 117 at risk for other adverse events and 0 affected. It also lists 0 deaths. These are the posted counts; the record does not provide additional event descriptions in the listed serious-event terms.
These figures should be read as registry-reported counts, not as proof that no adverse events occurred outside the categories or reporting scope represented by the record. The registry does not give an adverse-event observation period, detailed event definitions, or an explanation of how events were collected. It also does not explain whether the figures cover all enrolled subjects or only those with safety information. The listed at-risk counts should not be treated as proof that every subject had complete safety follow-up.
This was a diagnostic comparison, and the intervention named in the record was an antigen test. The adverse-event listing does not describe test-related symptoms or other clinical outcomes separately. The figures cannot establish a causal relationship between testing and events. They are a limited account of the safety information entered in the registry, and the absence of reported events in these categories is not a broader conclusion about safety.
12. What the Result Does, and Does Not, Mean
The record defines a clinically relevant diagnostic question: among symptomatic outpatients who were positive by rt-PCR, what proportion were also positive by the Quidel Sofia SARS Antigen FIA? It identifies the antigen specimen as a mid-turbinate swab and describes rt-PCR on nasopharyngeal swabs. It also identifies sensitivity as the primary endpoint and specifies a 1-day timeframe.
However, the registry record does not report the observed sensitivity, the number of rt-PCR-positive subjects, or a confidence interval. It therefore does not show the magnitude or precision of the primary result. The study status is terminated, but the reason is not reported. The enrollment entry does not establish the number with interpretable results or the number included in the endpoint analysis.
Even if a sensitivity estimate were available, it would answer only the conditional question defined by the endpoint. In general, it would not by itself describe the proportion of antigen-positive subjects who are rt-PCR-positive, the rate of positive antigen results among rt-PCR-negative subjects, or all aspects of diagnostic performance. The registry does not report a complete set of diagnostic accuracy measures.
The reference test and specimen methods are part of the interpretation. The endpoint treats rt-PCR positivity as the reference definition, while the antigen and rt-PCR procedures use different specimen collection methods in the study descriptions. The record does not separate assay effects from specimen-related effects or report an independent adjudication of infection status.
Accordingly, this record supports an explanation of the intended comparison and the limitations of the reported information, but not a conclusion about how well the antigen test performed. The registry entries do not establish that the test did or did not identify infection reliably, and they do not support a treatment or care recommendation.
13. Why This Trial Matters Statistically
Diagnostic studies ask a different statistical question from randomized treatment trials. Rather than estimating the effect of assigning one treatment instead of another, this study is described as comparing a diagnostic test result with a reference result. The endpoint focuses on the proportion of reference-positive subjects who were antigen-positive. Clear definition of that denominator is essential because a sensitivity estimate does not describe every aspect of test performance.
The record also illustrates why specimen collection is part of a diagnostic comparison. Antigen testing used mid-turbinate swabs, while the brief summary describes nasopharyngeal swabs for rt-PCR. A comparison of results from these procedures is informative about the testing approaches as recorded, but does not isolate the assay from the method of specimen collection.
Statistical interpretation depends on more than the name of an endpoint. The estimate, denominator, uncertainty interval, handling of uninterpretable results, and analysis population all affect how readers understand the evidence. In this record, the endpoint definition is present, but its observed value and confidence interval are not reported. The registry lists 0 analyses, and key analysis details are not reported. This makes the distinction between a planned measure and a posted result especially important.
The entry also demonstrates that status and enrollment alone do not supply an outcome. It lists enrollment of 117 and a terminated status, but gives no reason for termination or account of usable test results. Those details provide study context, not a substitute for the diagnostic estimates. A statistically careful reading recognizes what the design set out to measure while keeping the unavailable result and its uncertainty unresolved.
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 direct limitation in interpreting this record is that the primary endpoint result is not reported. There is no observed sensitivity value, confidence interval, or underlying count of antigen-positive subjects among rt-PCR-positive subjects. The number of reference-positive subjects is also absent, so the endpoint denominator and the precision of any estimate cannot be assessed.
The registry describes different specimen collection methods for the two tests: mid-turbinate swabs for antigen and nasopharyngeal swabs for rt-PCR in the brief summary. The comparison therefore cannot be interpreted as isolating assay performance from specimen collection based on the registry description. The record does not report a separate assessment of these components.
The study status is terminated, and the reason is not reported in the registry record. The record lists enrollment of 117 but does not state whether that enrollment was reached as planned, how many subjects had valid results for both tests, or how many were included in the primary analysis. The registry does not report handling of missing, invalid, or indeterminate test results, nor does it describe a detailed analysis population.
The record lists 0 analyses and does not provide a statistical analysis plan, a multiplicity strategy, or details of the method used to calculate the confidence interval. It also does not provide enough information to assess the characteristics of enrolled participants beyond their description as symptomatic outpatients. These are limitations of the information in the registry record; they do not establish that any particular data problem or analytic bias occurred.
Finally, the listed adverse-event counts have limited context. The record does not specify the observation period or provide further event details. The counts should not be treated as a comprehensive assessment of safety or as evidence of causation.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Diagnostic Performance of an Antigen Test for SARS-CoV-2 Infection (COVID-19) — NCT04610489.
- Registry record last updated 2021-08-17; status last verified 2021-08.
- Results first posted 2021-08-17.
- 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
NCT04610489 describes a single-group diagnostic comparison of the Quidel Sofia SARS Antigen FIA with rt-PCR among outpatients with symptoms compatible with COVID-19. The registry lists enrollment of 117, a start date of 2020-11-13, a primary completion date of 2021-03-10, and a terminated status. The reason for termination is not reported in the registry record.
The primary endpoint is sensitivity: the proportion of rt-PCR-positive subjects who were antigen-positive, with a timeframe of 1 day. The record does not report the observed endpoint value, its confidence interval, or the underlying test-result counts. It lists two outcome measures and 0 analyses. Serious adverse events are listed as 0 among 117 at risk, other adverse events as 0 among 117 at risk, and deaths as 0. The event observation period and further safety details are not reported.