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The Stratus® CS Acute Care™ D-dimer assay (DDMR) is an in vitro diagnostic test for the quantitative measurement of cross-linked fibrin degradation products (D-dimer) in human citrated or heparinized plasma on the Stratus® CS analyzer. The Stratus® CS Acute Care™ DDMR assay is intended for use in conjunction with a non-high clinical pretest probability (PTP) assessment model to exclude pulmonary embolism (PE) disease and as an aid in the diagnosis of venous thromboembolism (VTE) [deep vein thrombosis (DVT) or pulmonary embolism (PE)]. This assay is for use by trained health care professionals in the clinical laboratory and point of care (POC) settings.

The Stratus® CS Acute Care™ D-Dimer method is a two-site sandwich assay based upon solid phase Radial Partition Immunoassay (RPIA) technology. In this procedure, dendrimer linked monoclonal antibody is added to the center portion of a square piece of glass fiber paper in the DDMR TestPak. This antibody recognizes a distinct antigenic site on the D-dimer molecule. Sample is then added onto the paper where it reacts with the immobilized antibody. After a short incubation, a conjugate consisting of enzyme-labeled monoclonal antibody directed against a second distinct antigenic site on the D-dimer molecule is pipetted onto the reaction zone of the paper. During this second incubation period, enzyme-labeled antibody reacts with the bound D-dimer, forming an antibodyantigen-labeled antibody sandwich. The unbound labeled antibody is later eluted from the field of view of the Stratus® CS STAT Fluorometric Analyzer (Stratus® CS analyzer) by applying a substrate wash solution to the center of the reaction zone. By including substrate for the enzyme within the wash solution, initiation of enzyme activity occurs simultaneously with the wash. The enzymatic rate of the bound fraction increases directly with the concentration of D-dimer in the sample. The reaction rate can then be measured by an optical system that monitors the reaction rate via front surface fluorescence. All data analysis functions are performed by the microprocessor within the analyzer.

Acceptance Criteria and Device Performance for Stratus® CS Acute Care™ D-Dimer Assay

This document summarizes the acceptance criteria and performance of the Stratus® CS Acute Care™ D-Dimer assay as described in the provided 510(k) summary (K110303).

1. Table of Acceptance Criteria and Reported Device Performance

The study evaluated the performance of the Stratus® CS Acute Care™ D-Dimer assay against a clinical cutoff of 450 ng/mL [µg/L] (FEU) for the exclusion of Pulmonary Embolism (PE).

Acceptance Criteria (Implied by Predicate Device Equivalence and Clinical Relevance for PE Exclusion):
While explicit numerical acceptance criteria for sensitivity, specificity, and NPV are not directly stated as pass/fail thresholds, the study aims to demonstrate substantial equivalence to the Innovance D-Dimer assay and clinical utility for PE exclusion, implying that the performance metrics should be comparable to or ideally exceed those required for safe and effective PE exclusion. For D-dimer assays used to exclude PE, high sensitivity and negative predictive value (NPV) are critical. The reported values are generally considered acceptable for this application.

Reported Device Performance:

Citrated Plasma: In all patients

Citrated Plasma: In Patients with low and moderate pre-test probability

Heparinized Plasma: In all patients

Heparinized Plasma: In Patients with low and moderate pre-test probability

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

• Citrated Plasma: 730 consecutive patients initially, 655 patients remaining after exclusions for final analysis.
• Heparinized Plasma: 468 consecutive patients initially, 427 patients remaining after exclusions for final analysis.
• Data Provenance: The study was a multi-center study. The document does not specify the countries of origin but states it's a "multi-center study." The data is prospective, collected from consecutive patients presenting to the emergency department with suspected PE.

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

The document does not explicitly state the number of experts used to establish the ground truth or their qualifications in detail. However, the ground truth for PE diagnosis appears to be established through a combination of imaging methods (e.g., spiral CT and/or VQ scan) for patients with positive D-dimer and/or high PTP, and a three-month follow-up for patients with negative D-dimer/low/moderate PTP or negative imaging results. This implies that the diagnosis of PE was made by medical professionals (e.g., radiologists, clinicians) utilizing established diagnostic protocols but does not specify individual expert roles for establishing a "ground truth" for the test set.

4. Adjudication Method for the Test Set

The document does not describe an explicit adjudication method (e.g., 2+1, 3+1) for establishing the ground truth diagnoses. The diagnostic process involved imaging (spiral CT, VQ scan) and clinical follow-up for three months. It is implied that standard clinical practices and interpretations were followed for these diagnostic procedures, rather than a specific consensus or adjudication process among multiple independent experts to establish the ground truth for each case.

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

No, an MRMC comparative effectiveness study involving human readers with and without AI assistance was not performed. This study focuses on the performance of the device (assay) itself in a standalone manner, rather than as an aid to human interpretation.

6. If a Standalone Study Was Done

Yes, a standalone study of the algorithm's performance (the D-dimer assay) was done. The reported sensitivity, specificity, and negative predictive value are directly from the assay's performance against the established clinical ground truth for PE. There is no human-in-the-loop component for these reported performance metrics.

7. The Type of Ground Truth Used

The ground truth used was a combination of:

• Imaging Data: Spiral CT and/or VQ scans were used for patients with positive D-dimer results and/or high pre-test probability (PTP).
• Outcomes Data (Clinical Follow-up): Patients with negative D-dimer results and low or moderate PTP (or negative imaging results) were followed for three months to evaluate potential development of PE. This follow-up serves as an outcome-based ground truth to confirm the absence of PE.

8. The Sample Size for the Training Set

The document does not specify a separate training set. This 510(k) submission describes a clinical validation study, implying that the D-dimer assay and its cutoff of 450 ng/mL [µg/L] (FEU) were already established, likely based on previous research or predicate device characteristics. The study described here acts as a test set for validating the performance of the assay rather than for training a new algorithm.

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

As no explicit training set is described, the method for establishing ground truth for a training set is not applicable to the information provided. The study focuses on evaluating the assay's performance on a validation dataset.

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The Stratus® CS Acute Care™ D-dimer (DDMR) method is an in vitro diagnostic test for the quantitative measurement of cross-linked fibrin degradation products (D-dimer) in human citrated or heparinized plasma. The Stratus® CS Acute Care™ DDMR method is intended for use as an aid in the diagnosis of venous thromboembolism (VTE) [deep vein thrombosis (DVT) or pulmonary embolism (PE)]. This method is for use by trained health care professionals in the clinical laboratory and point of care (POC) settings.

The Stratus® CS Acute Care™ D-dimer Calibrator (DDMR CalPak) Catalog, No. CDDMR-C, is an in vitro diagnostic product intended to be used for calibration of the Stratus® CS Acute Care™ Ddimer (DDMR) method.

The Stratus® CS Acute Care™ D-dimer Dilution Pak (DDMR DilPak), Catalog. No. CDDMR-D, is an in vitro diagnostic product intended to be used in conjunction with the Acute Care™ DDMR TestPak, Catalog. No. CDDMR for the measurement of samples with elevated levels of D-Dimer.

The Stratus® CS Acute Care™ DDMR procedure is a two-site sandwich assay based upon solid phase Radial Partition Immunoassay (RPIA) technology. In this procedure, dendrimer linked monoclonal antibody is added to the center portion of a square piece of glass fiber paper in the DDMR TestPak. This antibody recognizes a distinct antigenic site on the D-dimer molecule. Sample is then added onto the paper where it reacts with the immobilized antibody. After a short incubation, a conjugate, consisting of enzyme-labeled monoclonal antibody directed against a second distinct antigenic site on the DDMR molecule is pipetted onto the reaction zone of the paper. Durine this second incubation period, enzyme-labeled antibody reacts with the bound D-dimer, forming an antibody-antigen-labeled antibody sandwich. The unbound, labeled antibody is later eluted from the field of view of the Stratus® CS analyzer by applying a substrate wash solution, to the center of the reaction zone. By including substrate for the enzyme within the wash solution, initiation of the enzyme activity occurs simultaneously with the wash. The enzymatic rate of the bound fraction increases directly with the concentration of D-dimer in the sample. The reaction rate can then be measured by an optical system that monitors the reaction rate via front surface fluorescence. All data analysis functions are performed by the microprocessor within the analyzer.

The provided 510(k) summary does not contain acceptance criteria for the device in the traditional sense of performance targets that must be met. Instead, it aims to demonstrate substantial equivalence to a predicate device by showing comparable performance, particularly regarding precision and accuracy, across different usage settings (laboratory vs. point-of-care).

The study described focuses on reproducibility (precision) and correlation (accuracy against the predicate).

Here's an breakdown of the available information:

1. Table of Acceptance Criteria and Reported Device Performance

As mentioned, explicit acceptance criteria are not stated. The study aims to demonstrate comparability to the predicate device. The performance is reported in the context of reproducibility and correlation.

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

• Test Set Sample Size:
  • Reproducibility: For each plasma pool level (L1 and L2) at each location (Lab, ED, CCU) within each of the three Point-of-Care sites, the "number of samples tested = 20." This refers to the number of replicates for the precision study, which was "4 reps per day for 5 days."
  • Correlation:
    • POC Site 1 (Lab v ED): 64 samples
    • POC Site 1 (Lab v CCU): 62 samples
    • POC Site 2 (Lab v ED): 67 samples
    • POC Site 2 (Lab v CCU): 65 samples
    • POC Site 3 (Lab v ED): 74 samples
    • POC Site 3 (Lab v CCU): 75 samples
• Data Provenance: The studies were performed at "three different locations (clinical laboratory (LAB, Emergency Department (ED) and Cardiac Care Unit (CCU) within three external evaluation sites." The document does not explicitly state the country of origin but implies clinical settings. The data appears to be prospective as it involves active testing for the purpose of this submission.

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

This device is an in vitro diagnostic test for D-dimer levels, not an imaging or diagnostic AI system requiring expert interpretation of images. Therefore, the concept of "experts used to establish ground truth" as it would apply to imaging studies is not relevant here. The ground truth for D-dimer levels would be the measured values themselves, and the study compares the agreement between measurements obtained in different settings (lab vs. POC) or against a "predicate" device/method.

4. Adjudication Method for the Test Set

Not applicable. As this is not an imaging or qualitative diagnostic study, there is no adjudication process in the traditional sense for establishing ground truth from multiple expert interpretations. The "ground truth" for each sample is its D-dimer concentration as measured by either the laboratory method or the predicate device.

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

No, an MRMC comparative effectiveness study was not done. This device is an in vitro diagnostic test, not an AI-based diagnostic tool requiring human readability or interpretation. The study compares instrument performance in different settings (Lab, ED, CCU) with different operators, but it's not framed as human readers improving with AI vs. without AI assistance.

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

Yes, this study represents a form of standalone performance evaluation for the device. The device measures D-dimer levels automatically; the "human-in-the-loop" here refers to the operators performing the test, rather than interpreting results that an AI would output. The study specifically addresses performance with "non-laboratory" personnel (ED/CCU) to support point-of-care use, demonstrating the device's robust standalone performance regardless of operator expertise (within trained health care professionals).

7. The Type of Ground Truth Used (expert consensus, pathology, outcomes data, etc.)

The ground truth for this type of device is the quantitative measurement of D-dimer concentration, typically established by a reference method or the predicate device. The comparison data shows measurements from different operational settings (Lab, ED, CCU) and implicitly compares the new device's derived values to those obtained by the laboratory-based predicate or a standard laboratory setting.

8. The Sample Size for the Training Set

The document does not explicitly mention a "training set" in the context of machine learning or AI models, as this is a chemical assay, not an AI device. The equivalent of "training" for such an assay would be the internal development and optimization of the assay's reagents and methodology by the manufacturer. The document does not provide details on the sample sizes used during the internal development or validation phase that led to the final product.

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

Given that this is a chemical assay, the concept of "ground truth for a training set" as it relates to AI is not applicable. The assay is based on established biochemical principles and calibrated using known D-dimer concentrations (as mentioned in the "Calibrator" section, where D-dimer in a liquid buffered bovine protein matrix with stabilizers is used). The calibration itself establishes the relationship between the signal detected by the instrument and the D-dimer concentration. This process is part of standard assay development and quality control.

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