Rapid SARS-CoV-2 IgG Antibody Testing in High Risk Healthcare Workers: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Rapid SARS-CoV-2 IgG Antibody Testing in High Risk Healthcare Workers (NCT04334876), a na na study. The primary outcome is Number of Participant Health Care Workers With a Positive Rapid, At-home, Point-of-care (POC) SARS-CoV2 IgG Antibody Test..

2. Clinical Question

The study also set out to evaluate seroconversion in this high-risk population and identify possible candidates for convalescent plasma donation for therapy or prophylaxis. A secondary outcome concerned the number of healthcare workers willing to be plasma donors if appropriate. Its result is not reported in the registry record. The record describes a diagnostic-testing study rather than a trial comparing clinical treatments. Its central statistical question is therefore descriptive: how many participants had a positive test under the study's testing and reporting process? The absence of a comparator means that the record cannot establish a difference between testing approaches or between treated groups.

3. Trial Design

The registry describes a completed, single-group study sponsored by Indiana University. It is identified as NCT04334876 and titled “Rapid SARS-CoV-2 IgG Antibody Testing in High Risk Healthcare Workers.” The recorded condition is SARS-CoV-2. The phase is listed as not applicable, allocation as not applicable, and masking as none. No randomized comparison is described.

The study started on 2020-04-01, with primary completion recorded as 2020-11-01. Enrollment was 571. Participants used an at-home, finger-prick SARS-CoV-2 IgG antibody test. The record says that participants self-administered the point-of-care test and self-reported at their convenience; testing and reporting took approximately 15 minutes. At-home follow-up testing was allowed every 3 weeks after reporting, with a total of 3 tests possible.

The participant flow reported for the primary outcome distinguishes consent from test-result submission. Of the 571 who consented, 71 were lost to follow-up. The remaining 500 completed the survey and submitted point-of-care test results. Within that group, 58 participants completed a second follow-up point-of-care test and 15 completed a third. These are follow-up counts, not results indicating how many tests were positive.

The primary outcome is the number of healthcare workers with a positive rapid at-home point-of-care IgG test. The description says positive tests were assessed for confirmation using a serum antibody test. The registry record does not report the number of positive point-of-care tests, the serum confirmation findings, or a statistical analysis of either result. It also does not report a detailed protocol for combining repeat tests into the primary outcome.

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

Analysis population for the primary outcome, as defined in the registry: There was a total of 571 subjects consented. Of these, 71 were lost to follow-up, giving a total of 500 subjects who completed the survey and submitted results for the POC test. Of these 500, 58 subjects did a second follow up point of care test, and 15 patients completed a 3rd test.

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 Number of Participant Health Care Workers With a Positive Rapid, At-home, Point-of-care (POC) SARS-CoV2 IgG Antibody Test., measured over Subjects self-administered the at home POC test and self-reported at their convenience. Testing/reported took approx 15min. Follow up at home testing allowed q 3 weeks post-reporting for a total of 3 at-home tests possible.

The primary endpoint is a count: the number of participant healthcare workers with a positive rapid, at-home, point-of-care SARS-CoV-2 IgG antibody test. A count records how many participants meet the stated outcome definition. It is not itself a rate or percentage; interpreting a count as a frequency in the study population also requires a clearly defined denominator and outcome-assessment population.

The endpoint addresses the study's stated aim of evaluating a rapid home test in high-risk healthcare workers. The description adds that positive point-of-care tests were assessed for confirmation using a serum antibody test. That confirmation step is relevant because the rapid test result and the serum test result are distinct measurements. The registry record does not report their respective results, how many participants were tested for confirmation, or how confirmation findings were summarized.

Repeated home testing was possible, with up to 3 tests described. The record reports how many participants completed second and third tests, but it does not state in detail whether the primary count refers to an initial test, any positive test during follow-up, or another rule for handling repeat results. That outcome-definition detail is not reported in the registry record. The endpoint is useful as a direct descriptive measure only when the tested population, assessment time, and rule for repeat results are clear. Without the positive count and those details, the registry does not permit a numerical estimate of the observed frequency or its precision.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The record's primary outcome is a binary event summarized as a count of participants: whether a participant had a positive rapid at-home IgG test. A count and a proportion answer related but different questions. The count gives the number meeting the outcome definition; a proportion relates that count to a specified denominator. The registry reports the number who completed and submitted results, but it does not report the primary positive count or explain in detail which participants formed the analysis population. No proportion can be stated without the outcome count, and none should be inferred from the participant-flow figures.

What does a confidence interval express?

In general, a confidence interval describes the uncertainty around an estimate under a specified statistical method. For a binary outcome, an interval around a proportion can help show how much the estimate may vary because only a sample of a target population was observed. Its interpretation depends on the estimate, denominator, sampling assumptions, and interval method. The registry record reports no interval for the primary outcome, and it does not name an interval method. Precision for the positive-test result therefore cannot be assessed from the registry record.

What does the single-group design allow?

In general, a single-group descriptive study can report how often an outcome occurred among the participants assessed. Without a comparator group, it cannot estimate a between-group contrast under random assignment. This record lists allocation as not applicable and describes a single-group study, so there is no randomized control arm against which to interpret the test count. A descriptive count would also depend on who enrolled, who completed testing, and how the outcome was defined; it would not by itself establish performance in other populations or settings.

How do repeat tests affect interpretation?

The record allowed repeat at-home testing every 3 weeks, with up to 3 tests possible. It reports that 58 participants completed a second test and 15 completed a third. In general, repeated measurements from the same person may be correlated: a participant's results are not necessarily independent observations. Analyses that treat repeated test results as independent can understate uncertainty if that dependence is ignored. A participant-level endpoint, such as whether a participant ever tested positive, requires a rule for combining the repeated results. The registry record does not report that rule or a statistical method for handling repeated tests. It also does not report whether the primary outcome was based on a particular test occasion or on results across follow-up.

Why distinguish the rapid test from serum confirmation?

The study description says positive point-of-care tests were assessed for confirmation using a serum antibody test. These are separate stages of measurement. In general, confirmation findings can help describe agreement or disagreement between tests, but such an assessment requires the number tested at each stage and the results of each test. Those details are not reported in the registry record. No estimate of agreement, sensitivity, specificity, or other diagnostic-performance measure is reported, and none can be reconstructed from the participant counts alone.

What do the planning assumptions mean?

In general, a sample-size calculation is a planning exercise that asks how many participants a hypothetical study might need under specified assumptions. The record's planning illustration is described as using a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of the observed effect. It specifies participants per arm for non-time-to-event outcomes. These assumptions describe an illustration, not the design of this single-group study: the registry does not describe two randomized arms. The illustration is not an observed power calculation and does not establish that the completed study had a particular power. The numerical planning outputs and any protocol-based sample-size justification are not reported in the registry record.

Over-dispersion is a general issue for count data when variation exceeds what a chosen probability model expects. In general, accounting for extra variation can widen uncertainty estimates and prevent overconfident inference. The primary outcome is described as a count of participants with an event, rather than a measure of variation across counts. No over-dispersion assessment or count-model analysis is reported in the registry record, so it should not be attributed to the study's analysis.

Finally, no formal analysis results are posted in the registry record. There is no reported statistical test, adjusted estimate, confidence interval, or model for the primary endpoint. Statistical interpretation is therefore limited to the design and participant-flow information that the record does report.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("High Risk Healthcare Workers")
n      <- c(500)
events <- c(8)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  High Risk Healthcare Workers  500  8  1.6  0.7  3.1  0.8  3.1  0.8  3.1

11. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures: the primary count of healthcare workers with a positive rapid at-home IgG test and a secondary outcome concerning willingness to be a convalescent plasma donor if appropriate. It also describes evaluating seroconversion as a study aim. The result for the secondary outcome and any seroconversion result are not reported in the registry record. The record lists no analyses, and no multiplicity adjustment or strategy for prioritizing statistical tests is reported.

Multiplicity matters in general when several outcomes or tests are examined: the more opportunities to declare a finding, the more important it is to specify which outcomes are primary and how inference across them will be handled. The registry identifies a primary endpoint, but does not report a statistical analysis plan or adjustment for multiple comparisons. It is not possible to determine whether such plans existed outside the registry record.

For missing data, the record says 71 of the 571 consented participants were lost to follow-up and 500 completed the survey and submitted point-of-care results. It does not report why those participants were lost, whether their outcomes were sought through another source, or how missing outcomes were handled in any analysis. A complete-case analysis, imputation, or another approach is not reported in the registry record. The 500 participants with submitted results should therefore not be assumed to be the analysis population for every outcome.

The record reports 58 second tests and 15 third tests among participants who completed the survey and submitted results. It does not describe how missing repeat tests were handled or how repeat measurements contributed to the primary outcome. No defined analysis population beyond the enrollment and follow-up counts is reported in the registry record. These omissions limit assessment of selection, missingness, and the comparability of outcome denominators.

12. 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's adverse-event fields list the high-risk healthcare worker group with 571 participants at risk for serious adverse events and 0 affected. The other adverse-event fields also list 571 at risk and 0 affected. The death count is 0, and no serious adverse-event terms are listed. These are the recorded safety figures for the group.

These entries are counts in the registry record, not a comparative safety analysis. Because the study is single-group and does not describe a control arm, the figures cannot be used to compare adverse events between groups. The record does not provide event definitions, detailed surveillance procedures, or a narrative explaining how adverse events were collected. Such information is not reported in the registry record.

A recorded count of 0 affected should be read as the registry's reported value, not as proof that an event was impossible or that every potential event was captured. The record also does not provide participant-level exposure details or an analysis of uncertainty around the safety counts. These fields should therefore be interpreted narrowly: the registry lists no affected participants or deaths in the reported categories, while the methods and completeness of safety ascertainment are not described in detail.

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

The record documents a study of at-home rapid SARS-CoV-2 IgG antibody testing in high-risk healthcare workers and gives useful information about enrollment and follow-up. It states that 571 participants consented, 500 completed the survey and submitted point-of-care results, and some participants completed repeat tests. It also records a single-group design with no masking and no separate comparator.

Those details do not reveal the primary outcome. The number of participants with a positive rapid test is not reported in the registry record, nor are the results of serum antibody confirmation. The secondary donor-willingness result and any result for seroconversion are also not reported. A missing result is not evidence of no positive tests, no seroconversion, or no willingness to donate. It means the outcome cannot be quantified from the registry record.

Even if a positive-test count were available, a descriptive count would answer a limited question about participants assessed in this study. It would not by itself show how the rapid test compares with another strategy, whether results generalize to other groups, or what a positive result means for an individual. The record does not report comparative diagnostic-performance estimates or a formal analysis of the serum confirmation step.

The figures for follow-up show that not all consented participants are represented among those who submitted results, while the handling of missing outcomes is not described. Repeat testing also introduces a question about whether results refer to an individual test occasion or a combined participant-level outcome. The registry record does not resolve that question. The reported safety fields list 0 affected for serious and other adverse-event categories and 0 deaths, but provide limited information about safety ascertainment.

Accordingly, the record supports describing the study's purpose, design, and reported participation. It does not support an estimate of the primary test-positive frequency or a conclusion about test performance, donor eligibility, or clinical benefit.

14. Why This Trial Matters Statistically

This study is statistically notable because its main outcome is a straightforward count, while the registry does not report that count. That distinction illustrates why reporting the outcome value is essential: enrollment and completion figures describe participation, but they do not answer how many participants met the endpoint. Without the event count, readers cannot estimate the observed frequency or its precision.

The record also highlights how a study's design sets limits on interpretation. This was a single-group study, not a randomized comparison. Its stated purpose included validating a rapid at-home test and assessing positive results with serum antibody testing, but the record does not provide the results needed to quantify those assessments. A design can address descriptive questions while still leaving comparative questions unanswered.

Follow-up and repeated testing add further statistical considerations. The record distinguishes 571 consented participants from 500 who completed the survey and submitted results, and reports smaller groups completing second and third tests. These counts make clear that the tested population and the population eligible for repeat assessment are not interchangeable. Transparent rules for missing observations and repeated measures would help readers understand which participants and test results inform each endpoint; those rules are not reported in the registry record.

Finally, the record's planning illustration is based on hypothetical two-arm assumptions, whereas the actual design is single-group. Keeping planning calculations separate from the completed study's design prevents readers from treating illustrative sample sizes as evidence of observed power or as a justification for the enrolled sample. The central statistical lesson is that design, outcome definition, denominators, missingness, and complete outcome reporting are all needed to interpret a diagnostic-testing study responsibly.

15. Limitations

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

The primary limitation for interpreting results is that the registry record does not report the positive-test count, despite identifying it as the primary outcome. It also does not report the serum confirmation results, secondary donor-willingness result, or a result for the stated seroconversion aim. Without those values, the principal study findings cannot be quantified.

The record reports 71 participants lost to follow-up from 571 who consented, while 500 completed the survey and submitted test results. It does not describe the reasons for loss to follow-up or how missing outcomes were handled. This prevents assessment of whether participants with observed results differed from those without reported results. The record also does not define an analysis population for each outcome.

Repeat testing was allowed, and the record gives counts for participants completing second and third tests. It does not specify how repeat test results were incorporated into the primary endpoint or how incomplete repeat testing was handled. That limits interpretation of the endpoint's time frame and participant-level meaning.

The study had no separate comparator group, so it cannot provide a randomized between-group comparison. Although the description says positive rapid tests were assessed using serum antibody testing, the registry does not report the number undergoing confirmation or the paired results needed to assess diagnostic agreement. A detailed statistical analysis plan, confidence intervals, and formal analyses are not reported. The safety fields list no affected participants, but the registry provides limited detail about how adverse events were ascertained.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Rapid SARS-CoV-2 IgG Antibody Testing in High Risk Healthcare Workers — NCT04334876.
• Registry record last updated 2023-04-26; status last verified 2023-04.
• Results first posted 2021-09-16.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

NCT04334876 is a completed, single-group study sponsored by Indiana University, titled “Rapid SARS-CoV-2 IgG Antibody Testing in High Risk Healthcare Workers.” It enrolled 571 high-risk healthcare workers to use an at-home, finger-prick rapid SARS-CoV-2 IgG test. The study started on 2020-04-01 and primary completion was recorded as 2020-11-01.

The primary outcome was the number of participants with a positive rapid point-of-care IgG test, with positive tests assessed for serum confirmation. The record reports 500 participants completing the survey and submitting results, after 71 were lost to follow-up; 58 completed a second test and 15 a third. The primary positive count, confirmation findings, secondary donor-willingness result, and formal analyses are not reported in the registry record.

The adverse-event fields list 0 affected in both serious and other categories, with 0 deaths. No comparator group is described.