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Focus Diagnostics' Plexus™ EBV IgM Multi-Analyte Diagnostics test kit is intended for qualitatively detecting the presence or absence of human IgM class antibodies to viral capsid antigen (VCA), and heterophile antibodies in human sera. The test is indicated as an aid in the diagnosis of EBV infection and EBV-associated infectious mononucleosis.

The performance of this assay has not been established for use in the diagnosis of nasopharyngeal carcinoma and Burkitt's lymphoma, for testing of immunocompromised patients, for use by a point of care facility or for use with automated equipment. This assay has not been evaluated for donor screening.

Multiplexed Immunoassay for the Qualitative Detection of Human IgM Antibodies to Epstein-Barr Virus

The Focus Diagnostics Plexus™ EBV IgM uses an Antigen Bead suspension that contains two distinct EBV antigen bead types (VCA and Heterophile) and one process control bead type that fluoresce at different wavelengths and/or intensities.

The Focus Diagnostics Plexus™ EBV IgM is a three step procedure.

1. Patient sera are diluted, and the diluted sera are incubated with Antigen Beads. If EBV antibodies are present, then the antibodies bind to the corresponding antigen beads.
2. Phycoerythrin-conjugated goat Anti-human IgM (Conjugate) is added, binds to the bound EBV antibody (if present), and forms a Conjugate-EBV antibody-antigen bead sandwich.
3. Fluorescence from each distinct EBV antigen bead type is measured and compared against a Cutoff Calibrator.

Plexus EBV IgM Multi-Analyte Diagnostics Acceptance Criteria and Study Details

1. Table of Acceptance Criteria and Reported Device Performance

The provided document does not explicitly state "acceptance criteria" in a table format with pre-defined thresholds. Instead, it presents performance data (positive and negative percent agreements) against predicate devices and then justifies substantial equivalence. Based on the comparative studies, the implicit acceptance criteria are that the device's performance should be comparable to or better than the FDA-cleared predicate devices.

2. Sample Size and Data Provenance

• Test Set Sample Size:
  • Prospective Samples: 723 samples (723 for VCA IgM, 723 for Heterophile IgM)
  • Retrospective Samples: 150 samples (150 for VCA IgM, 150 for Heterophile IgM)
• Data Provenance: The studies were conducted at three United States testing sites: a hospital laboratory located in the Northeast, a pediatric hospital laboratory located in the Mid-West, and Focus Diagnostics. Samples included both prospective (n=723) and retrospective (n=150) specimens. The samples were sequentially submitted to the laboratory, archived, and masked.

3. Number of Experts and Qualifications for Ground Truth

The document does not explicitly state the number of individual experts or their qualifications who directly established the "ground truth" for the test set. Instead, it refers to "consensus predicate" and "predicate rapid test."

For VCA IgM, the ground truth was established by a "consensus predicate" involving a combination of:
* A FDA-cleared commercially available ELISA
* A FDA-cleared commercially available immunofluorescent (IFA) test
* A FDA-cleared commercially available flow cytometry-based immunoassay.

For Heterophile IgM, the ground truth was established against a "FDA cleared heterophile rapid test."

The qualifications of the individuals who performed these predicate tests are not specified but would typically be trained laboratory personnel.

4. Adjudication Method for the Test Set

• VCA IgM: A "consensus based algorithm (2/3)" was used to determine the predicate result for comparison with the Plexus VCA IgM result. This means that at least two out of the three predicate devices had to agree on the result (positive or negative) for a consensus to be reached.
• Heterophile IgM: The document states that the Plexus EBV Heterophile IgM analyte was tested against a "FDA cleared heterophile rapid test," implying a direct comparison rather than a consensus among multiple predicates for this analyte.

5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study

No Multi-Reader Multi-Case (MRMC) comparative effectiveness study was mentioned. The study compares the device's performance directly against predicate devices, not human readers with or without AI assistance.

6. Standalone (Algorithm Only) Performance

Yes, a standalone performance study was done. The entire study focuses on the performance of the Plexus EBV IgM Multi-Analyte Diagnostics device (algorithm only, as it is an in vitro diagnostic assay) against predicate devices without human interpretation as part of its core function, other than potentially reading the results of the predicate devices.

7. Type of Ground Truth Used

The ground truth used was based on comparison with predicate devices, which are themselves FDA-cleared diagnostic assays.

• For VCA IgM, it was a "consensus predicate" combining results from an ELISA, IFA, and flow cytometry-based immunoassay.
• For Heterophile IgM, it was a "FDA cleared heterophile rapid test."
  Additionally, a "Typical Antibody Response Classification" table (Plexus EBV Serological Status) outlines an algorithm for classifying EBV infection status using various serological markers, including VCA IgM and Heterophile Antibody. This table serves as a reference for interpreting the combined results in the context of disease diagnosis.

8. Sample Size for the Training Set

The document does not specify a separate "training set" or its sample size. The performance studies described involve prospective and retrospective samples used for comparison with predicate devices. This suggests a validation study rather than a development and training paradigm typical of machine learning algorithms that require distinct training sets. Since this is an immunoassay, the "training" would be tied to the assay's development and optimization, not a separate dataset for an algorithm.

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

As no explicit training set is mentioned in the context of algorithm development, the method for establishing ground truth for a training set is not applicable or detailed in the provided document. The performance evaluation relies on comparing the device's results against established FDA-cleared predicate methods.

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