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Immunoassay for the in vitro quantitative determination of free thyroxine in human serum and plasma.

The Elecsys® test principle is based on competition principle. Total duration of assay: 18 minutes (37° C).
• 1st incubation (9 minutes): Sample (15 µL) and a specific anti-T4 antibody labeled with a ruthenium complex (75 µL).
• 2nd incubation (9 minutes): After addition of biotinylated T4 (75 µL) and streptavidin-coated microparticles (35 µL), the still-free binding sites of the labeled antibody become occupied, with formation of an antibody-hapten complex. The entire complex is bound to the solid phase via interaction of biotin and streptavidin.
The reaction mixture is aspirated into the measuring cell where the microparticles are magnetically captured onto the surface of the electrode. Unbound substances are then removed with ProCell. Application of a voltage to the electrode then induces chemiluminescent emission which is measured by a photomultiplier (0.4 second read frame).
Results are determined via a calibration curve which is instrument-specifically generated by 2-point calibration and a master curve provided via the reagent bar code.

The provided text describes a 510(k) summary for the "Elecsys® FT4 Assay," a device for the in vitro quantitative determination of free thyroxine in human serum and plasma. The acceptance criteria and the study proving the device meets these criteria are detailed through comparisons to a predicate device, the Enzymun-Test® FT4 (K900883).

Here's the breakdown of the information requested:

1. Table of Acceptance Criteria and Reported Device Performance

The acceptance criteria are implicitly defined by comparing the performance characteristics of the Elecsys® FT4 to its predicate device, Enzymun-Test® FT4. The goal is to demonstrate substantial equivalence, meaning the new device is as safe and effective as the predicate.

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

• Sample Size for Method Comparison:
  • For the Elecsys® FT4 compared against the Enzymun-Test® FT4: N = 315
  • For the Enzymun-Test® FT4 compared against itself (as a predicate, likely for its own method comparison studies): N = 77
• Sample Size for Precision: 60 for the Elecsys® FT4 at each control level. For the predicate, the N varied from 117 to 120.
• Data Provenance: Not explicitly stated (e.g., country of origin, retrospective/prospective). This information is typically found in the full study report, not necessarily in a 510(k) summary. Given the context of in vitro diagnostic assays, the samples would likely be human serum and plasma, but their origin is not specified.

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

This information is not applicable to this type of device and study. This device is an in vitro diagnostic (IVD) assay designed to quantitatively measure a biomarker (free thyroxine). The "ground truth" for such devices is established by reference methods or validated comparative methods (like the predicate device in this case), not by expert consensus on image interpretation or clinical diagnosis. The performance is assessed by analytical accuracy, precision, sensitivity, and specificity against these established methods or known spiked concentrations.

4. Adjudication Method for the Test Set

This is not applicable as the ground truth is established through quantitative analytical measurements against established methods, not through expert review and adjudication.

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 type of study is relevant for imaging devices or AI algorithms where human interpretation is involved. The Elecsys® FT4 Assay is an automated quantitative immunoassay, not a device requiring human interpretation through reading images or cases.

6. If a Standalone (Algorithm Only Without Human-in-the-Loop Performance) Was Done

Yes, the performance reported for the Elecsys® FT4 is a standalone (algorithm only) performance. This device is an automated immunoassay system that performs the measurement and calculation of free thyroxine levels without human intervention during the assay process. The results are generated directly by the instrument based on its electrochemical detection and built-in calibration curve.

7. The Type of Ground Truth Used

The ground truth for evaluating the Elecsys® FT4 Assay is primarily established through:

• Reference Method Comparison: Comparison against the predicate device, Enzymun-Test® FT4. This implies that the predicate device's results are considered a valid reference for "ground truth" for demonstrating substantial equivalence.
• Analytical Standards: Precision and sensitivity are determined using control samples with known concentrations and spiked samples, which serve as the "ground truth" for these performance characteristics.
• Known Interferents/Analytes: Specificity studies use known concentrations of potentially interfering substances or cross-reacting analytes, where the expected outcome (no interference, or specific cross-reactivity) serves as the ground truth.

8. The Sample Size for the Training Set

The document does not explicitly state the sample size for a "training set." For an IVD assay like Elecsys® FT4, the "training" aspect is more related to method development, reagent optimization, and establishing the master calibration curve, which is distinct from the concept of a training set in machine learning. The data provided focuses on the validation of the final assay.

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

As mentioned above, the concept of a "training set" and its "ground truth" in the machine learning sense is not directly applicable here. For the development and establishment of the assay itself (analogous to 'training' in a broad sense):

• Master Calibration Curve: The master curve is provided via the reagent bar code and is instrument-specifically generated by 2-point calibration. This curve is developed using a comprehensive set of calibrators with precisely known concentrations of the analyte (FT4). These known concentrations establish the "ground truth" for the dose-response relationship of the assay.
• Reagent Selection and Optimization: During the development phase, various reagent formulations and conditions would be tested against samples with pre-determined FT4 levels (perhaps measured by highly accurate reference methods or gravimetric preparation) to optimize performance characteristics like sensitivity, specificity, and precision.

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