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VIDAS® C. difficile Toxin A & B (CDAB) assay is an automated test for use on the VIDAS instruments for the qualitative detection of Clostridium difficile toxin A and toxin B in stool specimens using the ELFA technique (Enzyme-Linked Fluorescent Assay). The assay principle combines a two-step enzyme immunoassay sandwich method with a final fluorescent detection (ELFA). The Solid Phase Receptacle (SPR), a pipette tip-like device, serves as the solid phase as well as the pipetting device for the assay. The assay reagents are ready-to-use and pre-dispensed in the sealed reagent strips (STRs). Each of the four reaction steps are performed automatically by the VIDAS instrument. The reaction medium (sample/conjugate mixture) is cycled in and out of the SPR several times. Each step is followed by a wash cycle which eliminates unbound components. At the end of the VIDAS CDAB assay, results are automatically calculated by the VIDAS instrument. A test value as well as the qualitative result (positive, negative or equivocal) are provided on the result sheet for each sample.

AI/ML Overview

Here's a breakdown of the acceptance criteria and study information for the VIDAS® CDAB Assay based on the provided text, structured according to your request:

1. Table of Acceptance Criteria and Reported Device Performance

The provided document describes a 510(k) submission for a device claim extension of the VIDAS® CDAB Assay, not an initial submission where acceptance criteria would be explicitly detailed. Therefore, explicit "acceptance criteria" for the new claim extension are not clearly laid out as distinct pass/fail thresholds in the document.

Instead, the performance data is presented comparatively against a predicate device (the original VIDAS CDAB Assay, K072138, and Premier Toxins A&B) and a "gold standard" (CTA - Cytotoxicity Assay). The implication is that the new claim extension is acceptable if its performance is comparable to or better than the predicate and clinically acceptable as an aid in diagnosis.

Given this, I will infer the "acceptance criteria" from the predicate device's performance, as the purpose of a 510(k) is to demonstrate substantial equivalence.

Performance Metric	Acceptance Criteria (Inferred from Predicate/Clinical Acceptability)	Reported Device Performance (VIDAS® CDAB Assay)
Non-clinical/Analytical
Precision/Reproducibility	Comparable to predicate	Total precision: 7.4 – 37.6% CV
		Inter-assay precision: 6.8 – 26.8% CV
		Intra-assay precision: 2.9 – 26.3% CV
C. difficile strain types (A+/B+)	100% detection for A+/B+ strains	100% (23/23)
C. difficile strain types (A-/B+)	High detection rate for A-/B+ strains	83% (15/18) Note: 3 equivocal results
Limit of Detection (stool)	Comparable to predicate	Toxin A at ≥ 7.73 ng/mL; Toxin B at ≥ 4.55 ng/mL
Drug Interference	No significant interference from common drugs	Evaluated (Vancomycin, Metronidazole, Loperamide, Bismuth subsalicylate, Salicylate, Barium sulfate, Imodium, Pepto-Bismol) - specific results not quantified/detailed in summary
Clinical Studies (vs. CTA)
Sensitivity	Clinically acceptable for diagnostic aid (e.g., >80-85%)	88.3%; 95% CI: 81.2 – 93.5%
Specificity	High (e.g., >95-98%)	99.8%; 95% CI: 99.2 – 99.9%
Positive Predictive Value (PPV)	High (e.g., >90%)	98.1%; 95% CI: 93.5 – 99.8%
Negative Predictive Value (NPV)	High (e.g., >90%)	98.4%; 95% CI: 97.3 – 99.1%
Clinical Studies (vs. Predicate)
Positive Agreement	High agreement with predicate (e.g., >80%)	81.3%; 95% CI: 73.4 – 87.6%
Negative Agreement	Very high agreement with predicate (e.g., >95%)	99.5%; 95% CI: 98.8 – 99.9%
Global Agreement	High overall agreement with predicate (e.g., >90%)	97.1%; 95% CI: 95.9 – 98.1%
Additional Site Performance
Sensitivity (vs. CTA)	Clinically acceptable	88.0%; 95% CI: 68.8 – 97.5%
Specificity (vs. CTA)	High	95.1%; 95% CI: 86.3 – 99.0%
Total Agreement (vs. CTA)	High	93.0%; 95% CI: 85.4 – 97.4%

2. Sample Size Used for the Test Set and Data Provenance

Sample Size for Test Set: 1011 specimens
Data Provenance: Clinical study conducted in the USA and Europe. The document states it's a "summary of the non-clinical and clinical test results," implying that these are the results from the specific studies conducted to support the device. The term "retrospective or prospective" is not explicitly stated, but clinical studies for diagnostic devices typically involve prospective sample collection or the use of remnant/archived samples. Given the nature of a 510(k) for a claim extension, it's highly likely to be a combination, potentially including data from the original submission (K072138) and new data for the extension, though this is not explicitly clarified.

3. Number of Experts Used to Establish the Ground Truth for the Test Set and Qualifications of Those Experts

The ground truth for the clinical studies was primarily established using a "CTA" (Cytotoxicity Assay). This is a laboratory-based method, not dependent on human expert interpretation in the same way as, for example, a radiologist reading an image. Therefore, information about the "number of experts" or their specific "qualifications" for establishing this type of ground truth is not applicable and not provided in the document.

4. Adjudication Method for the Test Set

Not applicable. The ground truth (CTA) is a laboratory assay result, not subject to human interpretation discrepancies that would require an adjudication method.

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

No, a multi-reader multi-case (MRMC) comparative effectiveness study was not done. This type of study is more common for imaging diagnostics where human interpretation is a primary component of the diagnostic process. The VIDAS® CDAB Assay is an automated immunoassay.

6. Standalone (Algorithm Only) Performance

Yes, the performance data presented (Sensitivity, Specificity, PPV, NPV, and agreement rates) is the standalone performance of the VIDAS® CDAB Assay. It's an automated test, meaning its output is directly compared to the ground truth (CTA) without human intervention in its result generation or interpretation for the purpose of primary performance calculation. The "aid in diagnosing" phrasing implies a human-in-the-loop for final clinical decision-making, but the performance metrics themselves are standalone.

7. Type of Ground Truth Used

The primary ground truth used for the clinical studies was the Cytotoxicity Assay (CTA). This is a laboratory-based assay considered a reference standard for detecting C. difficile toxins.

8. Sample Size for the Training Set

The document does not explicitly mention "training set" or "validation set" sizes, which are typically associated with machine learning or algorithmic development. For an immunoassay like VIDAS, the "development" or "optimization" process involves various analytical studies (e.g., reagent optimization, buffer formulations) and may use smaller, targeted panels of positive and negative samples, but these are not typically referred to as a "training set" in the context of large-scale clinical data for algorithmic learning. The clinical performance data presented refers to the test set used for validation.

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

Since an explicit "training set" is not mentioned in the context of an algorithm or machine learning for this immunoassay device, the method for establishing its ground truth is not applicable. The device's underlying principles are based on biochemical reactions (ELFA) and not learned from large datasets in the same way an AI algorithm would be.

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