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The ZEUS ELISA Treponema pallidum IgG Test System is intended for the qualitative detection of specific IgG class antibodies to T. pallidum in human serum. The test may be used in conjunction with non treponemal testing and clinical findings to provide serological evidence of infection with T. pallidum. This test is for in vitro diagnostic use only.

This test is not intended for screening blood or plasma donors.

The ZEUS ELISA Treponema pallidum IgG Test System is designed to detect IgG class antibodies in human sera to Treponema pallidum. Wells of plastic microwell strips are sensitized by passive absorption with T. pallidum antigen. The test procedure involves three incubation steps:

1. Test sera are diluted with SAVE Diluent. During sample incubation, any antigen specific lgG antibody in the sample will bind to the immobilized antigen. The plate is washed to remove unbound antibody and other serum components.
2. Peroxidase conjugated goat anti-human IgG is added to the wells and the plate is incubated. The conjugate will react with IgG antibody immobilized on the solid phase in step 1. The wells are washed to remove unbound conjugate.
3. The microwells containing immobilized peroxidase conjugate with peroxidase substrate solution. Hydrolysis of the substrate by peroxidase produces a color change. After ten minutes have elapsed, the reaction is stopped and the color intensity of the solution is measured photometrically. The color intensity of the solution depends on upon the antibody concentration in the original test sample.

The Zeus Scientific Inc. ZEUS ELISA Treponema pallidum IgG Test System is intended for the qualitative detection of specific IgG class antibodies to T. pallidum in human serum. The test may be used in conjunction with non-treponemal testing and clinical findings to provide serological evidence of infection with T. pallidum. It is for in vitro diagnostic use only and not intended for screening blood or plasma donors.

Acceptance Criteria and Device Performance

The acceptance criteria for the ZEUS ELISA Treponema pallidum IgG Test System are implicitly demonstrated by the performance against the predicate device and the specified reproducibility metrics. While explicit quantitative acceptance criteria for clinical performance (e.g., specific sensitivity, specificity thresholds) are not individually listed for each study, the submission aims to demonstrate substantial equivalence to the predicate device.

The internal and external reproducibility studies provide quantitative acceptance criteria for precision (Total CV < 15% for reactive samples, < 25% for negative samples for repeatability; < 15% for reactive samples, < 50% for negative samples for reproducibility).

The reported device performance across various clinical studies is summarized below, with performance relative to the predicate device (TPPA) or clinical diagnosis.

Table 1: Device Performance Summary

Study Details

1. Sample Size Used for the Test Set and Data Provenance:

   • Prospective Studies:
     • 500 unselected samples from patients with a syphilis test ordered (US Mid-Atlantic, Northeast, and Zeus laboratories).
     • 500 unselected samples from pregnant women with a syphilis test ordered (US Mid-Atlantic, Northeast, and Zeus laboratories).
     • 1000 unselected samples from hospitalized patients (US: Monmouth, Mainline laboratories, and Zeus).
   • Retrospective Studies:
     • 223 banked known HIV-1 positive samples (New York vendor).
     • 280 RPR/TPPA positive samples (New York vendor).
     • 250 TPPA negative and 27 TPPA positive samples from pregnant women (New York vendor).
   • Reference Panels:
     • 157 samples from the CDC Syphilis Panel (origin unspecified, but typically US-based reference laboratories).
   • Precision/Reproducibility: 15 samples per study (prepared by Zeus Scientific, Inc.).

2. Number of Experts Used to Establish the Ground Truth for the Test Set and Their Qualifications: Not applicable. The ground truth for comparative clinical studies was established using a reference assay (TPPA or RPR) or clinical diagnosis, not by individual expert review of each case. For the CDC Syphilis Panel, the ground truth was "Clinical Diagnosis," implying a consensus or established diagnosis from medical records.

3. Adjudication Method for the Test Set: Not applicable. The studies relied on a reference assay (TPPA) for concordance analysis or established clinical diagnoses for the CDC panel. There is no mention of an adjudication process for discordant results between the device and the reference standard, nor for expert consensus in establishing the ground truth.

4. 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. The device is an ELISA test system, which provides an objective quantitative (OD value) and qualitative (Positive/Negative/Equivocal) result, not requiring human interpretation in the way an imaging AI algorithm would. Therefore, the concept of "human readers improving with AI vs. without AI assistance" does not apply here.

5. If a Standalone (i.e., algorithm only without human-in-the-loop performance) was done: Yes, the studies described are standalone performance evaluations of the ZEUS ELISA Treponema pallidum IgG Test System. The device output (OD value and interpretation) is generated directly by the assay without human interpretation as part of the primary diagnostic step. The results are compared against a reference standard or clinical diagnosis.

6. The Type of Ground Truth Used:

   • Reference Assay: For most clinical performance studies, the ground truth was established by a treponemal reference assay, specifically TPPA (Treponema pallidum Particle Agglutination assay), or in some cases, RPR (Rapid Plasma Reagin) for the retrospective RPR/TPPA positive samples.
   • Clinical Diagnosis: For the CDC Syphilis Panel, the ground truth was based on "Clinical Diagnosis" of syphilis disease.

7. The Sample Size for the Training Set: Not applicable in the context of an ELISA assay. ELISA assays are biochemical tests with fixed reagents and protocols, not machine learning algorithms that require a "training set" in the same sense. The linearity, analytical specificity (interfering substances, cross-reactivity), and detection limits studies are part of the analytical validation, not algorithm training.

8. How the Ground Truth for the Training Set was Established: Not applicable, as there is no "training set" for an ELISA assay as understood for AI/ML algorithms. The assay's performance characteristics are inherent to its biochemical design.

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