Rapid Identification and Susceptibility Testing of Pathogens From Blood Cultures: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Rapid Identification and Susceptibility Testing of Pathogens From Blood Cultures (NCT01898208), a randomized na study. The primary outcome is Duration of Antimicrobial Therapy (Hours).

2. Clinical Question

The study focused on whether rapid identification and resistance detection could inform antimicrobial management after a blood culture became positive. Its primary measure was duration of antimicrobial therapy, recorded in hours. The registry describes shorter broad-spectrum therapy and longer narrow-spectrum therapy as favorable directions, rather than defining one favorable direction for all antimicrobial use.

The central comparison is therefore not simply whether a test identifies pathogens more quickly. It concerns the relationship between rapid test information, communication or stewardship support, and the duration of treatment. The three-arm structure distinguishes testing with routine clinical communication from testing accompanied by expert review and recommendations. The registry record does not report a single primary-outcome estimate comparing those approaches, so it does not establish how large or precise any difference in duration was.

3. Trial Design

This was a completed, randomized, single-masked, parallel-group study sponsored by Mayo Clinic. The registry lists enrollment of 743 and gives the study start as 2013-08 and primary completion as 2014-08. The phase is listed as NA. The identity of the masked party and the procedures used to maintain masking are not reported in the registry record.

The control group followed standard Mayo practices for bacterial culture and susceptibility testing, without FilmArray testing. The FilmArray test group also received standard practices, with FilmArray Blood Culture ID Panel testing added. Its results were communicated to the service by phone in real time, 24 hours a day, 7 days a week. The third group received standard practices and FilmArray testing, plus review by an expert of the test result and medical record. The registry description says the expert would contact the primary service if an antimicrobial modification was indicated; the precise criteria and workflow are not reported in the registry record.

Random allocation is intended, in general, to reduce systematic differences between groups at the start of a study. The record does not describe the sequence-generation method, allocation concealment, or whether assignment was stratified. It also does not report whether the groups were analyzed according to assigned treatment or according to treatment received.

The primary endpoint was duration of antimicrobial therapy, with a timeframe described as approximately 4 days after enrollment. The registry lists 13 outcome measures and 23 analyses, including measures of time to antibiotic changes and pathogen identification, hospital stay, mortality, and antibiotic-associated toxicities or adverse events. The record does not give detailed protocols for these other measures in the registry record for this summary.

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: Subjects could have received more than one antimicrobial. Participants analyzed per variable below are expressed as (n=control, FilmArray test, and FilmArray+Stewardship)

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.

Population: Randomized subjects were excluded if they had a positive blood culture in the prior week, had not provided the state research authorization, previously enrolled in the study, died or transitioned to comfort care within 24 hours of enrollment, or had a negative Gram stain. Only non-excluded subjects were included in the baseline characteristics.

6. Primary Endpoint

The registry lists the primary outcome as Duration of Antimicrobial Therapy (Hours), measured over Approximately 4 days after enrollment.

The primary endpoint is duration of antimicrobial therapy, measured in hours. The registry defines the interval from the date and time of the antibiotic start order—or from the positive Gram stain if antibiotics began before the positive culture result—to the date and time of the antibiotic stop order. The stated timeframe is approximately 4 days after enrollment.

This measure is relevant to the study question because rapid diagnostic information and stewardship review may influence decisions about continuing, changing, or stopping antimicrobial treatment. The registry describes the desired direction differently by antibiotic spectrum: shorter duration of broad-spectrum antibiotics and longer duration of narrow-spectrum antibiotics were considered favorable. That distinction matters because a single reduction in total treatment time would not, by itself, express the registry’s stated goal for both types of therapy.

The record notes that a participant could receive more than one antimicrobial and that the participants analyzed could vary by variable. It does not report the endpoint-specific analysis population, the number of observations contributing to each comparison, or how overlapping courses of therapy were handled. Those details affect how a duration summary should be interpreted.

The endpoint is reported as a median with an inter-quartile range. In general, the median describes the middle of the observed distribution, while the inter-quartile range describes the spread of the central portion of that distribution. These summaries are useful when durations are skewed or include unusually long courses, but they do not replace an estimate of the between-group contrast with its uncertainty. Such a primary comparison is not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record identifies a randomized, single-masked, parallel-group design and a primary endpoint summarized by medians and inter-quartile ranges. It does not report the detailed statistical analysis plan, the primary comparison, or the numerical primary results. The methods below explain how these design and summary features are generally interpreted, while distinguishing those general principles from methods documented for this study.

What does random allocation contribute?

In general, random allocation aims to make treatment groups comparable with respect to both measured and unmeasured characteristics at the start of a trial. It does not guarantee that groups will be exactly alike, especially for characteristics that are uncommon or variable. It also does not by itself prevent bias after allocation: adherence, co-interventions, missing measurements, and outcome assessment can still differ. For this study, the registry states that allocation was randomized, but the method for generating the sequence, concealment of assignments, and any stratification are not reported in the registry record.

Parallel-group designs assign participants to an approach that is evaluated alongside the other approaches. The registry describes a control arm and two intervention arms. One intervention adds rapid FilmArray testing and real-time phone communication to standard practices; the other adds expert review and service contact to testing. This structure can distinguish the testing and communication approach from the added stewardship component, but the interpretation depends on the specific contrasts analyzed. The registry record does not identify a single primary contrast for the duration outcome.

Why report a median and inter-quartile range?

In general, duration data may be asymmetric: many observations can cluster at shorter durations while a smaller number extend much longer. A median is less influenced by unusually large values than a mean. The inter-quartile range describes the spread of the middle portion of the observations and gives readers context about variability. These summaries describe groups, but a reader assessing comparative effects also needs a defined contrast and an uncertainty measure, such as a confidence interval. Neither a numerical contrast nor its interval is reported in the registry record.

The endpoint’s direction is also category-dependent. The registry regards shorter broad-spectrum antibiotic duration and longer narrow-spectrum antibiotic duration as favorable. In general, an analysis that combines unlike categories into one overall duration could obscure that distinction. The record notes multiple categories or time points and does not reduce the primary outcome to one comparison. It does not report the full category-specific results or how any overall summary was constructed.

What does uncertainty mean?

In general, a confidence interval represents uncertainty in an estimated effect under the chosen model and analysis assumptions. A narrow interval indicates greater precision than a wide interval, but precision does not determine whether an effect is clinically important. A p-value summarizes how unusual data would be under a specified null hypothesis and model. It does not show the probability that the null hypothesis is true, nor does it measure the size of an effect. The registry record does not report primary-outcome confidence intervals or p-values, so precision and statistical compatibility cannot be assessed from the recorded details.

Over-dispersion is a general concern when outcome variability exceeds what a model assumes. If present and unaddressed, standard errors can be too small and intervals too narrow. The record does not identify a model for the primary endpoint, report a dispersion assessment, or describe any adjustment for it. It is therefore not possible to say whether over-dispersion was relevant or how it was handled in this study.

How should the planning illustrations be read?

The record describes planning illustrations based on an observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The illustrations use the stated fraction of the observed effect as the effect to detect. For time-to-event outcomes, the record says the illustrations give total events using the Schoenfeld method; other illustrations give participants per arm. These are planning calculations, not observed trial results and not observed power. The specific illustration values and effect fractions are not reported in the registry record for this summary. The illustrations also use a two-arm framework, whereas the trial record describes three groups, so a reader should not treat them as a complete account of every possible multi-group comparison.

In general, a planning calculation describes how much information a future study might need under stated assumptions. It does not establish that a completed study had adequate precision for every outcome, and it cannot replace the observed effect estimate and its uncertainty. The registry record does not report the original design assumptions, sample-size justification, or whether the planning illustration reflects the trial’s original design.

What analysis details are unavailable?

The registry record does not report the model used for duration, any covariate adjustment, the handling of ties or censoring, or the exact definition of the analysis population. It notes that participants could have more than one antimicrobial and that analysis counts could vary by variable, but it does not describe how repeated antimicrobial courses were accounted for. The masked party, allocation concealment, and detailed outcome-assessment procedures are also not reported. These omissions limit the ability to reproduce the analysis or assess how sensitive the findings might be to alternative analytic choices.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists 13 outcome measures and 23 analyses. Evaluating multiple outcomes, categories, time points, or pairwise contrasts creates a multiplicity issue: in general, the more statistical tests conducted, the greater the chance that at least one result appears notable by chance if each test is interpreted independently. This does not mean that any particular finding is false. It means that the planned comparisons and any approach to controlling or interpreting multiplicity are important for judging the strength of evidence.

The primary endpoint itself is described as involving several categories or time points and is not reduced to one comparison. The registry record does not report which contrast was designated as the principal inferential test, whether a hierarchy of outcomes was used, or whether a multiplicity adjustment was applied. It also does not report an analysis plan that would clarify which analyses were confirmatory and which were exploratory. Thus, the listed count of analyses alone cannot establish how multiplicity was handled.

Missing-data methods are not reported in the registry record. The record does not state how incomplete duration measurements, unavailable culture results, withdrawals, or other missing outcome information were handled, or whether missingness differed between groups. In general, missingness can affect interpretation when the chance of a measurement being absent is related to treatment or outcome. A complete-case result, an imputed result, and an analysis under other missing-data assumptions can differ; no such methods or sensitivity analyses are described.

Analysis populations are also not specified. The record notes that participants could receive more than one antimicrobial and that participants analyzed varied by variable, but it does not identify whether primary comparisons followed intention-to-treat, per-protocol, or another population definition. It does not report endpoint-specific denominators. As a result, the relationship between randomized assignment and the observations contributing to each analysis is not clear from the registry record.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry records serious adverse events as 0 for the control group, 0 for the FilmArray test group, and 0 for the FilmArray plus antimicrobial stewardship group. It records other adverse events as 3, 3, and 2 in those groups, respectively. The record does not list serious adverse-event terms, and deaths are not reported in the registry record.

These are recorded counts, not rates or comparative effect estimates. The registry entries do not explain the event definitions, severity criteria, collection period, attribution process, or whether events were independently adjudicated. They also do not provide uncertainty intervals or exposure-adjusted measures. Without those details, the counts cannot show whether groups differed in underlying risk.

In general, observing no recorded serious events does not establish that the true risk is zero. Rare events may not occur in a study even when a risk exists, and incomplete or differently intensive ascertainment can affect recorded counts. Likewise, a small difference in other-event counts does not by itself indicate a treatment effect. The safety entries should therefore be read as descriptive registry reports, not as proof of safety or harm.

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

The registry record describes a randomized comparison of standard practice, standard practice plus FilmArray testing, and standard practice plus FilmArray testing and stewardship review. It defines duration of antimicrobial therapy as the primary endpoint and explains the direction considered favorable for broad-spectrum and narrow-spectrum therapy. These details establish what the study set out to examine and how the endpoint was framed.

They do not provide a numerical answer about comparative treatment duration. The primary outcome involves several categories or time points and is not reduced to one comparison. No medians, inter-quartile ranges, effect estimates, confidence intervals, or p-values for the primary outcome are reported in the registry record. It is therefore not possible to determine from the recorded details whether any group had shorter or longer therapy, or how precisely such a difference was estimated.

The study’s motivating question also mentioned whether rapid identification and resistance detection would improve care or lead to increased cost. The listed outcomes include treatment timing, pathogen identification, hospitalization, mortality, and antibiotic-associated events, but a cost-specific measure or result is not reported in the registry record. The stated motivation should not be mistaken for evidence that a cost comparison was completed or that one approach was less costly.

In general, a randomized design can strengthen causal interpretation when allocation and follow-up are implemented appropriately and the analysis is suitable. However, the details needed to assess those conditions—including allocation procedures, analysis populations, missing-data handling, and endpoint-specific results—are not reported in the record. The design alone cannot substitute for outcome estimates.

The findings that can be described are limited to the recorded study design, endpoint definitions, listed outcome domains, and adverse-event counts. The record does not support a conclusion that any strategy improved care, reduced treatment duration, changed mortality, or altered costs. Absence of a reported result is not evidence of no effect; it means the registry record does not provide the information needed to estimate that effect.

13. Why This Trial Matters Statistically

This trial is statistically interesting because it evaluates more than the diagnostic test in isolation. The three-arm design distinguishes standard practice from rapid testing with real-time communication and from testing accompanied by stewardship review. That structure raises a useful design question: whether added diagnostic information and a clinical response to that information should be evaluated as separate components or as a combined care strategy.

The primary endpoint also illustrates why outcome definition matters. The registry considers shorter broad-spectrum therapy and longer narrow-spectrum therapy favorable. A single undifferentiated duration measure could fail to represent both aims. Separate categories or time points may better reflect the clinical question, but they create a more complex interpretation involving multiple summaries and comparisons. The record explicitly does not reduce the primary outcome to one comparison.

The study also highlights the difference between a study’s design and the evidence needed to interpret its results. Randomization can help balance groups, while medians and inter-quartile ranges can describe skewed duration data. But readers still need clear analysis populations, defined contrasts, effect estimates, and uncertainty measures. Those primary-outcome results are not reported in the registry record, so the design cannot be translated into a conclusion about comparative effect or precision.

Finally, the listed secondary outcomes show how a diagnostic intervention can be assessed across a chain of care: identification, treatment timing, antibiotic changes, hospitalization, and adverse events. In general, considering this range can help distinguish a faster laboratory result from a meaningful change in clinical processes. The registry record establishes that these domains were listed, but does not report their numerical findings in the registry record for this summary. That distinction is central to responsible statistical interpretation.

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 main limitation for interpreting this study from the registry record is the absence of a single primary-outcome comparison and its numerical results. The endpoint is described as having several categories or time points, but the record does not report category-specific medians, inter-quartile ranges, effect estimates, confidence intervals, or p-values. The direction and precision of any group differences therefore remain unknown.

Other analytic details that affect interpretation are not reported in the registry record. These include the randomization procedure, allocation concealment, identity of the masked party, endpoint-specific analysis populations, and handling of missing data. The record notes that participants could receive more than one antimicrobial and that the participants analyzed varied by variable, but it does not explain how courses or repeated observations were handled. This limits assessment of whether the analysis matches the randomized comparison.

The description of the stewardship arm is incomplete with respect to operational details. The registry says an expert reviewed the FilmArray result and medical record and contacted the primary service when an antimicrobial modification was indicated, but the criteria, timing, and consistency of that process are not reported in the registry record. The number and training of experts, and the approach to documenting recommendations, are also not reported.

The registry lists many outcomes and analyses, but does not report the statistical plan for handling multiple comparisons, the prespecified contrast, or whether outcome analyses were adjusted. Its planning illustration describes general assumptions, but the original sample-size justification and any interim analyses are not reported in the registry record. Finally, the safety entries lack definitions and follow-up details, while deaths are not reported. These gaps make the recorded adverse-event counts descriptive rather than a complete comparative safety assessment.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Rapid Identification and Susceptibility Testing of Pathogens From Blood Cultures — NCT01898208.
• Registry record last updated 2016-03-15; status last verified 2016-02.
• Results first posted 2016-03-15.
• 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

NCT01898208 is a completed randomized, single-masked, parallel-group study sponsored by Mayo Clinic. The registry lists enrollment of 743, a start date of 2013-08, and primary completion in 2014-08. The study compared standard bacterial culture and susceptibility testing with approaches adding FilmArray testing, with or without antimicrobial stewardship review.

The primary endpoint was duration of antimicrobial therapy in hours, summarized by median and inter-quartile range, over a timeframe described as approximately 4 days after enrollment. The registry considered shorter broad-spectrum therapy and longer narrow-spectrum therapy favorable. It lists 13 outcome measures and 23 analyses.

The primary outcome is not reduced to one comparison, and numerical primary results are not reported in the registry record. Serious adverse events are recorded as 0 in each group; other adverse-event counts are 3, 3, and 2. Deaths and detailed statistical methods are not reported in the registry record.