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510(k) Data Aggregation
(310 days)
The VIDAS® TOXO IgG Avidity assay is an automated qualitative test for the determination of anti-toxoplasma IgG avidity in human serum using the ELFA technique (Enzyme Linked Fluorescent Assay). The VIDAS® TOXO IgG Avidity assay is intended for use in conjunction with results from the VIDAS TOXO IgG II and must have a positive titer (> 8 IU/mL); other laboratory findings and clinical information to aid in the presumptive exclusion of a recently acquired (< 4 months) Toxoplasma gondii infection in pregnant women and patients with lymphadenopathy.
VIDAS TOXO IgG Avidity assay performance has not been established for prenatal screening, for newborn testing, for use in immunocompromised patients and in cases of endogenous or exogenous reinfection by Toxoplasma gondii. This assay has not been cleared or approved by the FDA for blood/plasma donor screening.
The VIDAS® TOXO IgG Avidity assay is an automated qualitative test for the determination of anti-toxoplasma IqG avidity in human serum using the ELFA technique (Enzyme Linked Fluorescent Assay). The VIDAS® TOXO IgG Avidity assay is intended for use in conjunction with results from the VIDAS TOXO IqG II and must have a positive titer (> 8 IU/mL); other laboratory findings and clinical information to aid in the presumptive exclusion of a recently acquired (< 4 months) Toxoplasma gondii infection in pregnant women and patients with lymphadenopathy.
The addition of a dissociating agent (such as urea) which disrupts the Ag-Ab link during an ELISA test has little effect on the high avidity Aq-Ab link, but great effect on that of weak avidity Ab. Comparison of results obtained with and without a dissociating agent corresponds to one measure of avidity.
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 predispensed in the sealed reagent strips. VIDAS TOXO IgG Avidity uses a dual strip comprising one reference strip and one test strip. The sample to be tested, after dilution, is dispensed into both sample wells of the dual strip: reference and test.
Anti-toxoplasma IgG present in the sample forms complexes with antigen coated to the solid phase. In the reference strip, non-specific antibodies are eliminated by washing, whereas specific antibodies remain coated to the solid phase. In the test strip, washing with the dissociating agent changes antibody links: high avidity antibodies remain bound to the solid phase, whereas low avidity antibodies are eliminated.
Alkaline phosphatase labeled with human anti-IgG antibody (conjugate) is then cycled in and out of the SPR, and binds with any human IgG coated on the interior of the SPR. Unbound conjugate is removed by washing.
All of the assay steps are performed automatically by the instrument. The reaction medium is cvcled in and out of the SPR several times. During the final detection step, the substrate (4-Methyl-umbelliferyl phosphate) is cycled in and out of the SPR. The conjugate enzyme catalyzes the hydrolysis of this substrate into a fluorescent product (4- Methyl-umbelliferone) the fluorescence of which is measured at 450 nm. Fluorescence is measured twice in the Reagent Strip's reading cuvette for each dual reagent strip. The first reading is a background reading of the substrate cuvette before the SPR is introduced into the substrate. The second reading is taken after incubating the substrate with the enzyme remaining on the interior of the SPR. The RFV (Relative Fluorescence Value) is calculated by subtracting the background reading from the final result. The RFV for the two assays (reference and test) appear on the result sheet. The intensity of the fluorescence is proportional to the concentration of antibodies present in the sample. At the end of the assay, results are automatically calculated by the instrument and then printed out.
The ratio between the quantity of high avidity antibodies (test strip) and the quantity of total antibodies (reference strip) provides an index that indicates antibody avidity in the tested sample.
The provided document describes the VIDAS® TOXO IgG Avidity Assay, an automated qualitative test for determining anti-toxoplasma IgG avidity in human serum. It is intended to aid in the presumptive exclusion of a recently acquired (≤ 4 months) Toxoplasma gondii infection in pregnant women and patients with lymphadenopathy, in conjunction with other laboratory and clinical findings.
1. Table of Acceptance Criteria and Reported Device Performance
The document does not explicitly state "acceptance criteria" as clear numerical targets. Instead, it presents several analytical performance metrics for the VIDAS® TOXO IgG Avidity Assay, which inherently serve as the data demonstrating its performance. For comparison, the document also includes data for the predicate device, VIDAS® TOXO IgM Assay.
| Performance Metric | VIDAS® TOXO IgG Avidity Assay Reported Performance |
|---|---|
| Within-run Precision | Low avidity: Mean avidity index = 0.1196, CV = 7.9% |
| Low avidity close to clinical decision point (C5): Mean avidity index = 0.2620, CV = 7.8% | |
| High avidity close to clinical decision point (C95): Mean avidity index = 0.3209, CV = 5.7% | |
| High avidity (medium): Mean avidity index = 0.5352, CV = 6.1% | |
| High avidity (high): Mean avidity index = 0.6843, CV = 7.1% | |
| Between-Run Precision | Low avidity: Mean avidity index = 0.1196, CV ≤ 0.1% |
| Low avidity close to clinical decision point (C5): Mean avidity index = 0.2620, CV ≤ 0.1% | |
| High avidity close to clinical decision point (C95): Mean avidity index = 0.3209, CV = 4.3% | |
| High avidity (medium): Mean avidity index = 0.5352, CV = 3.1% | |
| High avidity (high): Mean avidity index = 0.6843, CV = 2.1% | |
| Total Precision (within-run, between-run, between-day, between-lot, and between site) | Low avidity: Mean avidity index = 0.1196, CV = 8.4% |
| Low avidity close to clinical decision point (C5): Mean avidity index = 0.2620, CV = 9.7% | |
| High avidity close to clinical decision point (C95): Mean avidity index = 0.3209, CV = 7.4% | |
| High avidity (medium): Mean avidity index = 0.5352, CV = 7.0% | |
| High avidity (high): Mean avidity index = 0.6843, CV = 7.4% | |
| Cross-Reactivity | No clinically significant interference from samples with Rheumatoid Factors, Antinuclear antibodies, Epstein Barr virus, CMV, HAMA, HAV, HBV, HSV-2, Rubella, VZV (except 1 of 12 HSV-1 samples showed interference). |
| Interfering Substances | No interference from Hemoglobin (up to 300 µmol/L), Triglycerides (up to 30 mg/mL), Bilirubin (up to 510 µmol/L), Human albumin (up to 5 g/dL). |
| Drug Interference | No interference from Sulfamethoxazole, Sulfapyridine, Sulfasalazine, Spiramycin, Clindamycin, Trimethoprim, Sulfamethoxazole + Trimethoprim, Pyrimethamine (at specified concentrations). |
2. Sample Size for the Test Set and Data Provenance
The document refers to "non-clinical (analytical) comparison" data, which typically represents testing done for analytical performance rather than clinical validation of diagnostic accuracy with patient samples.
- Precision Studies:
- Within-run Precision: n = 80 replicates at each of 3 sites (total 240 replicates per avidity level).
- Between-Run Precision: n = 40 runs at each of 3 sites.
- Total Precision: n = 120 runs (2 runs per day, for 10 days with 2 reagent lots, at 3 sites).
- Cross-Reactivity: Number of samples varies by condition (e.g., 12 samples tested for HSV-1 disease, others are not specified with counts beyond "samples from patients with...").
- Interfering Substances: Not specified with sample counts but indicates testing was done up to certain concentrations.
- Drug Interference: Not specified with sample counts but indicates testing was done at specific drug concentrations.
Data Provenance: The document does not explicitly state the country of origin for the samples or if the data is retrospective or prospective. It is clinical laboratory data, generated during the analytical validation of the assay.
3. Number of Experts Used to Establish Ground Truth for the Test Set and Their Qualifications
The document describes analytical performance studies (precision, cross-reactivity, interference). For these types of analytical studies, the "ground truth" is typically defined by controlled experimental conditions (e.g., known concentrations, spiked samples, well-characterized panels) rather than expert clinical consensus. Therefore, expert involvement for establishing ground truth in this context is not applicable.
4. Adjudication Method for the Test Set
Adjudication methods (like 2+1, 3+1) are typically used in clinical studies to establish a consensus ground truth from multiple expert readings of patient cases. Since this document focuses on analytical performance rather than diagnostic accuracy with expert-adjudicated clinical cases, no such adjudication method is mentioned or relevant to the data presented.
5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done
No, the document does not describe a Multi-Reader Multi-Case (MRMC) comparative effectiveness study. The studies detailed are analytical performance evaluations of the assay itself, not studies comparing human reader performance with or without AI assistance. The device is a diagnostic assay, not an AI-powered image analysis tool or decision support system for human readers.
6. If a Standalone (Algorithm Only Without Human-in-the-Loop Performance) Was Done
Yes, the studies presented are standalone performance evaluations of the VIDAS® TOXO IgG Avidity Assay. The assay is an automated qualitative test that provides results directly. The analytical performance data (precision, cross-reactivity, interference) are all measures of the algorithm's/device's performance without human intervention in the result determination. The document states, "All of the assay steps are performed automatically by the instrument. The reaction medium is cycled in and out of the SPR several times. During the final detection step... results are automatically calculated by the instrument and then printed out."
7. The Type of Ground Truth Used (Expert Consensus, Pathology, Outcomes Data, etc.)
For the analytical studies presented, the "ground truth" was established by:
- Known Characteristics of Controls/Samples: For precision studies, standardized controls or characterized samples with known avidity levels were used.
- Known Presence/Absence of Interferents/Cross-Reactants: For cross-reactivity and interference studies, samples were either known to contain specific cross-reactants/interferents or were spiked with them at defined concentrations.
This type of ground truth is based on the intrinsic properties of the test materials and the controlled experimental setup, which is standard for analytical validation of in vitro diagnostic devices. Clinical ground truth (e.g., confirmed toxoplasmosis infection status based on pathology or long-term clinical outcome) would be established in a clinical performance study, which is distinct from the analytical studies described here.
8. The Sample Size for the Training Set
The document describes pre-market analytical performance data for a diagnostic assay. It does not mention a "training set" or "test set" in the context of machine learning or AI development. The data presented are from validation studies of the finished device. Therefore, information on a training set size is not applicable in this context.
9. How the Ground Truth for the Training Set Was Established
As explained in point 8, the concept of a "training set" for an AI or machine learning model is not applicable to the analytical validation of this in vitro diagnostic assay.
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