(319 days)
The AxSYM Toxo IqG Antibody assay is a Microparticle Enzyme Immunoassay (MEIA) for the quantitative measurement of IgG antibodies to Toxoplasma gondii in human serum or plasma (EDTA, heparin or sodium citrate) to aid in the determination of immune status. This product is not FDA cleared for use in testing blood or plasma donors.
The AxSYM Toxo IgG Antibody assay is a Microparticle Enzyme Immunoassay (MEIA) for the quantitative measurement of IgG antibodies to Toxoplasma gondii in human serum or plasma (EDTA, heparin or sodium citrate). It uses polystyrene microparticles coated with Toxoplasmosis gondii antigen (RH strain derived from HeLa cell cultures) as the solid phase and goat anti-human IgG antibody conjugated to alkaline phosphatase as the conjugate. It uses 4-Methylumbelliferyl Phosphate (MUP) as the enzyme substrate and is performed on an automated instrument.
Here's a breakdown of the acceptance criteria and study details based on the provided text:
1. Table of Acceptance Criteria and Reported Device Performance
The acceptance criteria are implied by the performance of the predicate device (VIDAS Toxo IgG) as well as the observed performance of the AxSYM Toxo IgG. The intent is to demonstrate at least comparable performance.
| Performance Metric | Acceptance Criteria (Implied by Predicate) | Reported Device Performance (AxSYM Toxo IgG) |
|---|---|---|
| Relative Sensitivity | ~96.0% - 98.4% (VIDAS study range) | 99.66% |
| Relative Specificity | ~97.8% - 97.9% (VIDAS study range) | 99.10% |
| Relative Agreement | (Not explicitly stated for predicate) | 99.34% |
| Percent CVs (Positive Panel/Control) | (Not explicitly stated for predicate) | 7.6% to 12.7% |
2. Sample Size Used for the Test Set and Data Provenance
- Sample Size: 1400 specimens
- Data Provenance: From pregnant women and random low-risk individuals. The study was conducted in two U.S. sites and one European site. (Retrospective, as these were "specimens" being tested, not newly collected for the study's primary purpose relative to the device).
3. Number of Experts Used to Establish the Ground Truth for the Test Set and Qualifications of Those Experts
The text does not explicitly state the number or qualifications of experts used. However, it indicates that discordant results were resolved using:
- IMx Toxo IgG Antibody assay (legally marketed device)
- Platelia Toxo IgG (legally marketed device)
- Sabin-Feldman dye test (a reference laboratory method, considered the most sensitive and specific for detecting IgG antibodies to toxoplasma, developed in 1948).
While specific "experts" are not mentioned, the use of a reference laboratory method (Sabin-Feldman dye test) implies specialized laboratory personnel with expertise in this established method.
4. Adjudication Method for the Test Set
A form of adjudication was used for discordant results.
- Method: Discordant results between the AxSYM Toxo IgG and the VIDAS Toxo IgG were resolved by testing with two other legally marketed devices (IMx Toxo IgG Antibody assay and Platelia Toxo IgG) and the Sabin-Feldman dye test. This implies a process where disagreements were arbitrated by multiple independent methods, especially the gold standard Sabin-Feldman dye test. This is an indirect adjudication process rather than direct expert consensus of, for example, a single image.
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. This study compares two devices (assays) rather than the performance of human readers with or without AI assistance.
6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) Was Done
Yes, this study represents a standalone performance evaluation of the AxSYM Toxo IgG antibody assay. It assesses the assay's performance characteristics (sensitivity, specificity) directly against a predicate device and reference methods, without involving human interpretation as part of the primary outcome measure.
7. The Type of Ground Truth Used
The ground truth was established by a combination of:
- Reference Laboratory Method: Sabin-Feldman dye test (considered the gold standard for Toxo IgG detection).
- Other Legally Marketed Devices: IMx Toxo IgG Antibody assay and Platelia Toxo IgG.
This represents a composite reference standard where highly regarded established methods are used to determine the true immune status for discordant results.
8. The Sample Size for the Training Set
The document does not mention a separate "training set." The study conducted was primarily a clinical performance evaluation of the final device against a predicate, using the 1400 specimens as a test set. This type of device (an assay) does not typically have a "training set" in the same way an AI/ML algorithm would, as it's not a learned model but rather an enzyme immunoassay.
9. How the Ground Truth for the Training Set Was Established
As no training set is described for this type of device, this question is not applicable. The development and validation of such an assay would involve extensive biochemical and analytical studies, but not a "training set" with ground truth in the context of machine learning.
§ 866.3780
Toxoplasma gondii serological reagents.(a)
Identification. Toxoplasma gondii serological reagents are devices that consist of antigens and antisera used in serological tests to identify antibodies toToxoplasma gondii in serum. Additionally, some of these reagents consist of antisera conjugated with a fluorescent dye (immunofluorescent reagents) used to identifyToxoplasma gondii from clinical specimens. The identification aids in the diagnosis of toxoplasmosis caused by the parasitic protozoanToxoplasma gondii and provides epidemiological information on this disease. Congenital toxoplasmosis is characterized by lesions of the central nervous system, which if undetected and untreated may lead to brain defects, blindness, and death of an unborn fetus. The disease is characterized in children by inflammation of the brain and spinal cord.(b)
Classification. Class II (performance standards).