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Remel Xpect® Flu A&B is a in vitro immunochromatographic test for the direct, qualitative detection of influenza A and influenza B viral antigens (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. A negative test is presumptive and it is recommended these results be confirmed by virus culture or an FDA-cleared influenza A and B molecular assay.

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 wells 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.

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Acceptance Criteria and Study Details for Remel Xpect® Flu A&B

1. Table of Acceptance Criteria and Reported Device Performance

The provided document primarily focuses on analytical sensitivity as the performance metric for this submission. While a single, overarching acceptance criterion isn't explicitly stated as a pass/fail threshold, the study's purpose is to demonstrate the device's ability to detect various influenza strains, including the newly added A/Anhui/1/2013 (H7N9). The "Detection Limit" column in the table below represents the reported device performance for each strain.

Note: The document explicitly states: "Although this test has been shown to detect the influenza A/California/04/2009 (H1N1) and A/Anhui/1/3012 (H7N9) viruses cultured from positive human specimens, the performance characteristics of this device with human specimens infected with these influenza A viruses have not been established." This indicates that the analytical sensitivity data presented here is for cultured viral strains, not directly from human clinical samples for the A/H1N1 and A/H7N9 strains mentioned.

2. Sample Size Used for the Test Set and Data Provenance

• Sample Size: The test set for analytical sensitivity consisted of 17 influenza strains (11 influenza A and 6 influenza B).
• Data Provenance: The data comes from laboratory testing of cultured viral strains. The country of origin for the data is not specified, but it is implied to be internal laboratory work conducted by Remel Inc. The study is a prospective experimental study in a controlled laboratory setting, not a retrospective analysis of clinical data.

3. Number of Experts Used to Establish the Ground Truth for the Test Set and Qualifications of Those Experts

Experts are not mentioned in the context of establishing ground truth for the analytical sensitivity test set. The ground truth for this type of test is typically based on the quantitated viral stock concentrations and the known presence/absence of the specific influenza strains.

4. Adjudication Method for the Test Set

Adjudication methods are not applicable and not mentioned for this analytical sensitivity study. The determination of a "positive endpoint" for each viral strain would be based on consistent visual readability of the test line by laboratory personnel following a defined protocol, not by expert consensus or adjudication of ambiguous results.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done

No, a multi-reader multi-case (MRMC) comparative effectiveness study was not done based on the provided text. The submission focuses on analytical sensitivity, not reader performance or human-AI interaction.

6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) Was Done

Yes, a standalone study was done. The analytical sensitivity study evaluates the device's ability to detect different influenza strains at specified concentrations without human interpretation variability being a primary variable. The Remel Xpect® Flu A&B is a visual read immunochromatographic test, meaning the "algorithm" is the biochemical reaction itself, and the "standalone" performance refers to its ability to react correctly to various concentrations of target analytes. While human visual interpretation is involved, the study assesses the inherent detection capability of the test.

7. The Type of Ground Truth Used

The ground truth used for the analytical sensitivity study is the known concentration (quantitation and titration) of well-characterized influenza viral strains. This is measured as TCID50/ml (50% tissue culture infectious dose) or CEID50/ml (50% chicken embryo infectious dose).

8. The Sample Size for the Training Set

The concept of a "training set" is not applicable to this device or study description. The Remel Xpect® Flu A&B is a chemical-biological immunoassay, not a machine learning or AI-driven diagnostic device that requires a training set.

9. How the Ground Truth for the Training Set Was Established

As stated above, a training set is not applicable to this device. Therefore, no ground truth for a training set was established.

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