(231 days)
The VIDAS® TOXO IgG II (TXG) assay is intended for use with a VIDAS® (Vitek ImmunoDiagnostic Assay System) instrument as a quantitative automated enzyme-linked fluorescent immunoassay (ELFA) for the measurement of Toxoplasma gondii-specific IgG in human serum or plasma (EDTA, heparin). It is intended for use as an aid in determination of immune status. It is not intended for use in testing (screening) blood or plasma donors.
The VIDAS TOXO IgG II (TXG) assay is an automated quantitative test that is performed in a VIDAS instrument. All assay steps and assay temperature are controlled by the VIDAS instrument. The assay principle combines a two step enzyme immunoassay sandwich method with a final fluorescent detection (ELFA). The Solid Phase Receptacle (SPR) serves as the solid phase as well as the pipetting device for the assay. Reagents for the assay are ready-to-use and pre-dispensed in the sealed reagent strips. All of the assay steps are performed automatically by the instrument. The VIDAS TXG kit contains 60 TXG Reagent Strips, 60 TXG SPRs, 1 bottle of calibrator, and 1 bottle each of Positive and Negative controls. Each VIDAS TXG assay requires one TXG Reagent Strip and one TXG SPR.
Here's a breakdown of the acceptance criteria and study details for the VIDAS TOXO IgG II (TXG) assay based on the provided text:
Acceptance Criteria and Reported Device Performance
The acceptance criteria are not explicitly stated as numerical targets in a formal "acceptance criteria" table. Instead, the study aims to demonstrate "substantial equivalence" to the predicate device. The performance metrics presented are relative sensitivity and relative specificity.
| Performance Metric | Acceptance Criteria (Implied for Substantial Equivalence) | Reported Device Performance |
|---|---|---|
| Relative Sensitivity | High (e.g., above a certain threshold, implicitly compared to predicate) | 98.45% (95% CI: 97.06%-99.29%) |
| Relative Specificity | High (e.g., above a certain threshold, implicitly compared to predicate) | 99.77% (95% CI: 99.33%-99.95%) |
Note: The FDA's 510(k) clearance process focuses on substantial equivalence to a legally marketed predicate device, rather than strictly defined numerical acceptance criteria like those sometimes seen for novel devices. The high sensitivity and specificity relative to the predicate were deemed sufficient to demonstrate substantial equivalence.
Study Details
2. Sample Size Used for the Test Set and Data Provenance
- Sample Size: 1940 serum samples.
- Data Provenance: Not explicitly stated (e.g., country of origin). The study is retrospective in nature as it tests existing serum samples with both the new device and the predicate device.
3. Number of Experts Used to Establish Ground Truth for the Test Set and Qualifications
- Number of Experts: Not applicable. The "ground truth" for the clinical testing was established by the predicate device (Abbott IMx Toxo IgG 2.0 Antibody Assay) acting as the reference comparator.
4. Adjudication Method for the Test Set
- Adjudication Method: For initial VIDAS equivocal samples, retesting was performed as directed in the package insert. The text mentions "there were 30 VIDAS equivocal results and 19 Abbott equivocal results" from the original 1940 samples. It doesn't specify further adjudication beyond the retesting of VIDAS equivocal samples. No inter-reader or expert consensus adjudication is mentioned, as the predicate device served as the primary comparison.
5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done
- No, an MRMC comparative effectiveness study was not performed. This study is for an in-vitro diagnostic (IVD) assay, which involves automated or semi-automated detection, not human reader interpretation of images or data that would typically necessitate an MRMC study.
6. If a Standalone (Algorithm Only Without Human-in-the-Loop Performance) Was Done
- Yes, the study describes the standalone performance of the VIDAS TOXO IgG II (TXG) assay. It is an "automated quantitative test" and an "automated enzyme-linked fluorescent immunoassay (ELFA)." The sensitivity and specificity reported are for the device itself against the predicate.
7. The Type of Ground Truth Used
- Type of Ground Truth: The ground truth was based on the performance of a predicate device – the Abbott IMx Toxo IgG 2.0 Antibody Assay. This means the study established the relative performance of the new device compared to an already legally marketed and accepted device.
8. The Sample Size for the Training Set
- Training Set Sample Size: Not explicitly stated. The document focuses on the performance of the final, developed assay. IVD assays like this typically undergo extensive development and internal validation, but the "training set" in the context of machine learning (which this device is not) doesn't directly apply here. The document details nonclinical testing (cross-reactivity, precision, linearity) which typically informs assay development and refinement.
9. How the Ground Truth for the Training Set Was Established
- Ground Truth for Training Set: Not applicable in the machine learning sense. For an IVD assay, the equivalent of "ground truth" for development would involve well-characterized reference materials, known positive and negative samples, and samples with various concentrations to establish assay parameters, linearity, and precision. The nonclinical testing section describes some of these processes:
- Cross-reactivity/Interference: 85 samples from patients with various disease states and known anti-T. gondii IgG status were used. This "known status" would be established through other validated methods.
- Linearity: Dilutions of 4 serum samples and the WHO standard were tested. The WHO standard is an internationally recognized reference material that provides a "ground truth" for specific concentrations.
§ 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).