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The IMMULITE® 2000 Free Thyroxine Assay is for in vitro diagnostic use with the IMMULITE 2000 Systems Analyzers - for the quantitative measurement of nonprotein-bound thyroxine (free T4) in serum and heparinized plasma, as an aid in the clinical assessment of thyroid status.

The IMMULITE 2000 Free T4 is a solid-phase, enzyme-labeled chemiluminescent competitive immunoassay. The solid phase (bead) is coated with monoclonal murine anti-T4 antibody. The liquid phase consists of alkaline phosphatase (bovine calf intestine) conjugated to T4. The patient sample and the reagent are incubated together with the coated bead for 30 minutes. During this time, free T4 in the sample competes with enzyme coniugated T4 in the buffer for a limited number of antibody binding sites on the bead. Unbound patient sample and enzyme conjugate are then removed by centrifugal washes. Finally, the chemiluminescent substrate is added to the reaction tube containing the bead and the signal is generated in proportion to the bound enzyme. The IMMULITE 2000 Free T4 procedure is a direct or single test assay, in the sense that its results are not calculated as a function of total T4, but interpolated from a (stored) standard curve calibrated in terms of free T4 concentrations.

Here's a breakdown of the acceptance criteria and study information for the IMMULITE® 2000 Free T4 assay, based on the provided text:

1. Table of Acceptance Criteria and Reported Device Performance

Note on Acceptance Criteria: For many analytical performance characteristics (like linearity, precision, sensitivity, and interference), the "acceptance criteria" are implied by adherence to CLSI guidelines and demonstrating performance comparable to or better than established methods/predicate devices. Specific numerical thresholds for acceptance, beyond what is reported as achieved, are not explicitly stated. The primary acceptance criterion for the overall device's substantial equivalence is its performance relative to the predicate device in terms of accuracy/correlation and other analytical characteristics.

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

• Accuracy/Correlation (Method Comparison):
  • Sample Size: 282 samples
  • Data Provenance: Not explicitly stated, but based on a "Method Comparison" against a predicate device, it implies prospective testing of patient or control samples using both devices. The origin country is not specified.
• Precision:
  • Sample Size: Six different material/sample pools (Pool 05-09 and Control). For each, two aliquots were assayed in two runs per day on 20 different days. This amounts to 80 measurements per material (2 aliquots * 2 runs/day * 20 days).
  • Data Provenance: Not explicitly stated, but typically generated in a controlled laboratory setting (e.g., at Siemens Healthcare Diagnostics).
• Linearity/Recovery:
  • Sample Size: 9 samples (calibrators and mixed calibrators). Five replicates of each sample were assayed.
  • Data Provenance: Laboratory generated.
• Interference (Endogenous & Cross-Reactivity):
  • Sample Size: Not specified for how many samples or replicates were tested for each interferent, but implies a series of controlled experiments.
  • Data Provenance: Laboratory generated.
• Limit of Blank (LoB) & Limit of Detection (LoD):
  • Sample Size: Not explicitly stated, but guided by CLSI EP17-A.
  • Data Provenance: Laboratory generated.

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

• This device is an in vitro diagnostic (IVD) assay for quantitative measurement of Free T4, not an imaging or diagnostic AI tool that requires expert interpretation of images/data for ground truth.
• The "ground truth" for the test set (e.g., the true Free T4 concentration for method comparison, linearity, or precision) would be established by:
  • Using reference materials with known concentrations.
  • Performance of the predicate device (ADVIA Centaur FrT4) for comparison studies.
  • Validated analytical methods as performed by laboratory professionals.
• Therefore, the concept of "number of experts used to establish ground truth" as it applies to subjective interpretation (like radiology reads) is not directly relevant here. Instead, it relies on the analytical accuracy and precision of established methods and technical expertise in laboratory testing and calibration.

4. Adjudication Method for the Test Set

• Not applicable as this is an IVD assay, not an AI diagnostic tool requiring subjective interpretation and adjudication. The "ground truth" for method comparison is the measurement by the predicate device (ADVIA Centaur FrT4).

5. If a Multi Reader Multi Case (MRMC) Comparative Effectiveness Study was Done

• No, an MRMC comparative effectiveness study was not done. This is an in vitro diagnostic assay measuring a biochemical marker, not a system that relies on human readers interpreting medical cases.

6. If a Standalone (i.e. algorithm only without human-in-the-loop performance) was Done

• Yes, the performance presented (e.g., precision, linearity, sensitivity, method comparison) is standalone performance of the IMMULITE 2000 Free T4 assay system (analyzer, reagents, and calibration software) without human-in-the-loop interpretation beyond standard laboratory procedures for running the assay and reviewing results. The "algorithm" here refers to the immunoassay chemistry and the instrument's computational processing of chemiluminescent signals to produce a quantitative result.

7. The Type of Ground Truth Used

The ground truth for the various performance studies can be categorized as:

• Predicate Device Measurements: For the accuracy/correlation (method comparison) study, the measurements from the ADVIA Centaur FrT4 assay served as the comparative 'ground truth'.
• Known Concentrations/Reference Materials: For linearity/recovery, limit of blank, and limit of detection, the ground truth was established using calibrators, known dilutions, or samples expected to contain no analyte, where the "true" concentrations are precisely defined.
• Statistical Definitions: Functional sensitivity is defined by a specific statistical criterion (20% CV), rather than an external "ground truth" measurement.

8. The Sample Size for the Training Set

• This document describes the validation of an immunoassay kit for an existing instrument platform (IMMULITE 2000). It is not an AI/machine learning device in the sense of requiring a "training set" of data for algorithm development. The assay's "learning" or calibration involves using specific calibrator materials with known concentrations to generate a standard curve, which is distinct from an AI training set. Therefore, this concept is not applicable here.

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

• As stated above, the concept of a "training set" for an AI algorithm is not applicable to this immunoassay device. The assay is calibrated using calibrators with precisely known concentrations of Free T4. The "ground truth" for these calibrators would be established through highly accurate reference methods or certified reference materials.

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