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In-vitro diagnostic automated assay for the quantitative determination of the von Willebrand antigen (VWF:Ag) in human plasma collected from venous blood samples in 3.2% sodium citrated tubes on the SYSMEX® CS-2500 analyzer.

As an aid used in the evaluation of patients aged 4 weeks and older with suspected or confirmed von Willebrand factor disorders and intended for prescription use.

Results of this test should always be interpreted in conjunction with the patient's medical history, clinical presentation and other laboratory findings.

Device Description

The vWF Ag is an immunoturbidimetric assay for the quantitative, WHO-standardized determination of von Willebrand factor (VWF) antigen concentration.

The vWF Aq kit consist of a Latex Reagent (4 x 2 mL) which is a suspension of small polystyrene particles (latex) coated with rabbit anti-human VWF antibodies. The Reagent Diluent (4 x 4 mL) is provided within the kit which is a solution containing glycine. The Reagent Diluent is intended for dilution of the Latex Reagent. The vWF Ag kit is completed by the Buffer (4 x 5 mL) which is a glycine buffer. All components contain sodium azide (

AI/ML Overview

Here's an analysis of the acceptance criteria and study details for the vWF Ag device, based on the provided text:

Acceptance Criteria and Device Performance

The document doesn't explicitly state "acceptance criteria" as a single, consolidated table with pass/fail values. Instead, it details performance characteristics established through various studies. I will present the reported device performance for several key metrics:

Metric	Acceptance Criteria (Implied by Study Design)	Reported Device Performance (vWF Ag on SYSMEX® CS-2500)
Measuring Interval (LoQ)	Accurate measurement at lower limit	LoQ established as 3.12% of norm; lower limit of 4% of norm is accurately measured.
Measuring Interval (Linearity)	Predefined maximum deviation: ≤ 20% absolute (for measured range ≤ 20% of norm), ±10.0% relative (for measured range > 20% of norm)	Linear across 3.6 to 399.7% of norm; met predefined maximum deviation criteria.
Endogenous Interferents	No interference up to indicated concentrations	No interference observed up to: Hemoglobin 712 mg/dL, Bilirubin (unconjugated) 30 mg/dL, Bilirubin (conjugated) 100 mg/dL, Lipids 549 mg/dL, Rheumatoid Factors 23 IU/mL
Exogenous Interferents	No interference up to indicated concentrations (various drugs)	No interference observed up to indicated concentrations for 23 listed drugs (e.g., Acetaminophen 156 µg/mL, Emicizumab 300 µg/mL) - See full list in original text
Heterophilic Antibodies	No susceptibility	No susceptibility observed towards human anti-mouse antibodies (HAMAs) or lupus anticoagulant.
High Dose Hook Effect	No high dose hook effect	No high dose hook effect up to 1213% of norm VWF:Ag.
Sample Carryover	No cross-contamination	No cross-contamination caused by one sample into another.
Reagent Carryover	No cross-contamination	No cross-contamination caused by one application into another.
Reproducibility (Total CV)	Not explicitly stated as a single value, but evaluated against established clinical laboratory standards (CLSI EP05-A3)	2.03 – 5.96% (Multicenter, USA)
Method Comparison (Passing-Bablok Regression)	Proposed and predicate devices provide equivalent results.	Sites Combined: y=1.04x - 4.60% of norm, r=0.982 (r²=0.965) - Meets equivalence criteria against predicate.

Study Details

2. Sample Sizes and Data Provenance

Measuring Interval (LoQ): Five independent low-analyte plasma pools.
Measuring Interval (Linearity): Not explicitly stated, but "a dilution series was prepared using a high plasma sample pool and a low plasma sample pool to equal 12 different dilutions."
Specificity (Interference): "Individual native samples with and without interferent" for paired-difference experiments. "Single native plasmas" for Rheumatoid factors. The number of samples per interferent testing is not specified.
Reference Interval:
- Blood group O: n = 147
- Blood group non-O: n = 159
- Blood group independent: n = 306
- Data Provenance: Three clinical study sites in the United States. The study involved apparently healthy subjects.
Pediatric Population Measurements:
- Blood group O: n = 21
- Blood group non-O: n = 26
- Total pediatric (independent of ABO blood group): n = 47
- Data Provenance: "healthy pediatric subjects".
Precision/Reproducibility:
- External Reproducibility (Multicenter): Three (3) external sites in the USA (Sites 1, 2, and 3). Test samples included three plasma pools and three control materials. Each site used 5 days, 2 runs/day, 3 replicates/run (3x5x2x3).
- Internal Precision (Single Site, Germany - Reagent Variability): One (1) site in Germany. 20 days, 2 runs/day, 2 replicates/run (20x2x2) with 3 different reagent lots.
- Internal Precision (Single Site, Germany - Calibrator Variability): One (1) site in Germany. 20 days, 2 runs/day, 2 replicates/run (20x2x2) with 3 different calibrator lots.
- Internal Precision (Single Site, Germany - Instrument Variability): One (1) site in Germany. 5 days, 2 runs/day, 4 replicates/run (5x2x4) on 3 SYSMEX® CS-2500 analyzers.
- Data Provenance: Mixed (USA and Germany), all prospective measurements for the study.
Method Comparison:
- Site 1 (Germany): N = 107
- Site 2 (United States): N = 115
- Site 3 (United States): N = 117
- Overall (Combined Sites): N = 339
- Data Provenance: One external site in Germany (Site 1) and two external sites in the United States (Site 2 and Site 3). The samples tested "ensured the intended use population was tested". This implies a mix of patient samples. Retrospective or prospective nature is not explicitly stated but generally for method comparison, collected clinical samples are used.

3. Number of Experts and Qualifications (for Ground Truth)

The document describes in-vitro diagnostic assay performance, which typically relies on laboratory measurements rather than expert human interpretation of images or clinical findings where "ground truth" and "experts" as in radiology studies would be directly relevant.

For the "Reference Interval" and "Pediatric Population" studies: These likely involved general medical professionals or phlebotomists for sample collection, and laboratory technicians for running the assays. The "ground truth" here is the biological sample itself and the reference standard used (WHO standard for calibration traceability). No "experts" in the sense of adjudicating findings (e.g., radiologists) were explicitly mentioned.

4. Adjudication Method (for Test Set)

Not applicable. This is an in-vitro diagnostic assay, not a device requiring human interpretation of results requiring adjudication for a test set. The performance is assessed based on quantitative measurements against predefined analytical performance metrics and comparison to a predicate device.

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

No. This is an in-vitro diagnostic device (an assay), not an imaging or diagnostic AI system that aids human readers. The document details a method comparison study between the proposed device and a predicate device, which is a different type of comparative effectiveness.

6. Standalone Performance (i.e., algorithm only without human-in-the-loop performance)

Yes, the studies reported are for the standalone performance of the vWF Ag assay on the SYSMEX® CS-2500 analyzer. This is an automated assay, meaning it operates without human-in-the-loop performance for result generation. Interpretations of historical context or other lab findings are mentioned as necessary in conjunction with the test results, but the test itself is standalone.

7. Type of Ground Truth Used

Measuring Interval, Specificity, Precision/Reproducibility: The "ground truth" for these analytical performance studies is based on:
- Known concentrations in prepared samples (e.g., dilutions from plasma pools, spiked samples with interferents).
- Reference materials (e.g., control materials, calibrators).
- WHO Standard (reagents traceable to WHO 6th International Standard Factor VIII / Von Willebrand Factor (07/316)).
Reference Interval & Pediatric Population: The "ground truth" is derived from empirically measuring VWF:Ag levels in a defined population of "apparently healthy subjects" using the device itself.
Method Comparison: The "ground truth" for comparison is the performance of the legally marketed predicate device (STA® - Liatest® VWF:Ag on the STA R Max® analyzer).

8. Sample Size for the Training Set

Not applicable. This document describes the performance of a VWF Ag assay, which is an immunoturbidimetric test, not an AI/ML algorithm that requires a training set in the conventional sense. The "training" for such a system would involve optimizing the assay's chemical reagents and instrument parameters, which is part of the development process but not disclosed as a distinct "training set" of data.

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

Not applicable, as there's no explicitly defined "training set" for an AI/ML algorithm. The assay's analytical performance and calibration are established using reference materials and pooled samples with known or established values, as described in point 7.

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