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REMEL's Xpect™ Flu A/B is a rapid in vitro immunochromatographic test for the direct, qualitative detection of influenza A and influenza B viral antigen (nucleoprotein) from nasal wash, nasal swab, and throat swab specimens from symptomatic patients. The test is intended as an aid in the rapid diagnosis of influenza A and influenza B viral infections. Negative tests should be confirmed by cell culture.

The Xpect™ Flu A/B is a chromatographic immunoassay for the qualitative detection of influenza A and influenza B viral antigens. The test device incorporates separate membrane strips for influenza A and for influenza B. To perform the test, the patient specimen is diluted and added to the sample well of the device. The mixture moves along the membranes by capillary action. If present, influenza A or B viral antigens in the patient sample bind anti-influenza A or B conjugated antibodies. A visible line forms as a complex of antibody-antigen-antibody coated colored particles is captured in the test region (T). Antibody coated colored particles not bound at the test line are later captured in the control region (C) containing goat anti-mouse antibody. A visible line will always appear in the control region indicating that the test is working properly. The presence of a control line combined with the absence of a visible test line is interpreted as a negative test result.

Acceptance Criteria and Device Performance Study for Xpect™ Flu A/B Device

This document describes the acceptance criteria and the study that demonstrates the performance of the Xpect™ Flu A/B device.

1. Table of Acceptance Criteria and Reported Device Performance

The provided text does not explicitly state pre-defined acceptance criteria (e.g., "Sensitivity must be > 90%"). Instead, it presents observed performance metrics. However, based on the clinical accuracy results, we can infer the implied acceptance criteria were met by the observed performance.

2. Sample size used for the test set and the data provenance:

• Overall Clinical Accuracy:
  • Total Samples for Flu A: 77 positive by culture, 314 negative by culture (Total = 391)
  • Total Samples for Flu B: 46 positive by culture, 345 negative by culture (Total = 391)
• Stratified by Specimen Type:
  • Nasal Wash: n=239 (40 Flu A positive, 199 Flu A negative; 36 Flu B positive, 203 Flu B negative)
  • Throat Swabs: n=30 (10 Flu A positive, 20 Flu A negative; 4 Flu B positive, 26 Flu B negative)
  • Nasal Swab: n=122 (27 Flu A positive, 95 Flu A negative; 6 Flu B positive, 116 Flu B negative)
• Data Provenance: The clinical trials were conducted at three sites in the United States (north, south, and east regions). The sites included a children's hospital (pediatric population), a university hospital (primarily adult population), and a reference laboratory (60% adult, 40% pediatric population). The data appears to be prospective clinical data collected specifically for this evaluation.

3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts:

The text does not specify the number or qualifications of experts used to establish the ground truth. It states that the ground truth for clinical accuracy was established by cell culture. While cell culture is a definitive method, the interpretation and execution of these cultures would be performed by trained laboratory personnel, but they are not explicitly referred to as "experts" in the context of adjudication or consensus.

4. Adjudication method for the test set:

The primary ground truth was established by cell culture. For discrepant results (samples that were culture positive but Xpect™ Flu A/B negative), RT-PCR was performed on some of the available samples. This indicates a secondary, confirmatory method was used for discrepant analysis, but not a formal expert adjudication panel. Specifically:

• For Influenza A, 4 out of 5 available discrepant samples were positive by RT-PCR.
• For Influenza A in Nasal Wash, 2 out of 3 discrepant samples were positive by RT-PCR.
• For Influenza A and B in Nasal Swab, 2 out of 4 discrepant specimens (1 Flu A, 1 Flu B) that were available were positive by PCR.

5. If a multi-reader multi-case (MRMC) comparative effectiveness study was done, If so, what was the effect size of how much human readers improve with AI vs without AI assistance:

No. This is a rapid in vitro diagnostic test for antigen detection. It is not an imaging device or an AI-driven diagnostic system that involves human readers interpreting results with or without AI assistance. Therefore, an MRMC comparative effectiveness study is not applicable and was not conducted.

6. If a standalone (i.e. algorithm only without human-in-the-loop performance) was done:

Yes, the performance data presented (sensitivity, specificity) reflects the standalone performance of the Xpect™ Flu A/B device. The device provides a qualitative result (positive or negative) based on the presence of visible bands, without human interpretation for the result itself, beyond observing the bands as per the instructions.

7. The type of ground truth used:

The ground truth used for clinical accuracy evaluation was cell culture. For some discrepant results, RT-PCR was used as a confirmatory method.

8. The sample size for the training set:

The document does not provide information about a separate "training set" in the context of machine learning or AI. This device is a rapid immunochromatographic test, not an AI/ML-based algorithm. The described studies are performance evaluations of the final device.

9. How the ground truth for the training set was established:

As this is not an AI/ML-based device, there is no "training set" in that context described. The studies outlined are for the validation of the device's performance against established diagnostic methods (cell culture).

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