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The i-STAT TBI Plasma test is a panel of in vitro diagnostic immunoassays for the quantitative measurements of glial fibrillary acidic protein (GFAP) and ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) in plasma and a semiquantitative interpretation of test results derived from these measurements, using the i-STAT Alinity Instrument. The interpretation of test results is used, in conjunction with other clinical information, to aid in the evaluation of patients, 18 years of age or older, presenting with suspected mild traumatic brain injury (Glasgow Coma Scale score 13-15) within 12 hours of injury, to assist in determining the need for a CT (computed tomography) scan of the head. A 'Not Elevated' test interpretation is associated with the absence of acute traumatic intracranial lesions visualized on a head CT scan.

The test is to be used with plasma prepared from EDTA anticoagulated specimens in clinical laboratory settings by a healthcare professional. The i-STAT TBI Plasma test is not intended to be used in point of care settings.

The i-STAT TBI Plasma cartridge is a multiplex immunoassay that contains assays for both ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) and glial fibrillary acidic protein (GFAP). The assays test for the presence of these biomarkers in a plasma sample and yield a semi-quantitative test interpretation based on measurements of both UCH-L1 and GFAP in approximately 15 minutes. The i-STAT TBI Plasma cartridge is designed to be run only on the i-STAT Alinity instrument.

The i-STAT Alinity instrument is a handheld, in vitro diagnostic device designed to run only i-STAT test cartridges. The instrument is the main user interface of the i-STAT System and functions as the electro-mechanical interface to the test cartridge. The instrument executes the test cycle, acquires and processes the electrical sensor signals converting the signals into quantitative results. These functions are controlled by a microprocessor.

The i-STAT Alinity System is comprised of the i-STAT Alinity instrument, the i-STAT test cartridges and accessories (i-STAT Alinity Base Station, Electronic Simulator and Printer).

Here's a breakdown of the acceptance criteria and study information for the i-STAT TBI Plasma cartridge with the i-STAT Alinity System, based on the provided text:

1. Table of Acceptance Criteria and Reported Device Performance

The document does not explicitly state pre-defined acceptance criteria in a table format. However, it presents clinical performance parameters for sensitivity, specificity, and negative predictive value (NPV). The implied "acceptance criteria" are derived from comparison to the predicate device and the clinical utility for reducing unnecessary CT scans.

Note: The document explicitly states that the device was deemed "substantially equivalent" to the predicate, and a "benefit-risk assessment was performed," suggesting that the performance metrics achieved were considered acceptable for its intended use and comparative to the existing predicate.

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

• Pivotal Study:
  • Sample Size: 1901 subjects (120 with positive CT, 1781 with negative CT).
  • Data Provenance: Prospectively collected and archived (frozen) plasma specimens. Subjects enrolled at 22 clinical sites in three countries: United States, Germany, and Hungary.
• Supplemental Fresh Specimen Study:
  • Sample Size: 88 subjects (29 with positive CT, 59 with negative CT).
  • Data Provenance: Freshly collected plasma specimens. Subjects enrolled across 4 clinical sites of the TRACK-TBI study in the United States.

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

• Number of Experts: At least two neuroradiologists, with a third neuroradiologist for adjudication if necessary.
• Qualifications of Experts: Neuroradiologists (specific years of experience or subspecialty certification not detailed, but implied by the term "neuroradiologist").

4. Adjudication Method for the Test Set

The adjudication method used was consensus interpretation between two neuroradiologists, with adjudication by a third neuroradiologist if necessary. This is commonly referred to as a "2+1" or "multiple reader, with adjudication" method.

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

No, an MRMC comparative effectiveness study comparing human readers with AI assistance versus without AI assistance was not described in this document. The clinical studies focused on the standalone diagnostic performance of the device itself (i-STAT TBI Plasma test interpretation) against a CT scan ground truth, not on evaluating human reader performance with or without the device. The device's output is an "interpretation of test results...to aid in the evaluation of patients...to assist in determining the need for a CT scan," suggesting it's designed to be used by a healthcare professional as an aid, but the study design doesn't directly measure the improvement of human readers through its use.

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

Yes, the clinical studies presented here (Pivotal and Supplemental) are effectively standalone performance studies for the i-STAT TBI Plasma test. The results (sensitivity, specificity, NPV) are reported for the device's interpretation ("Elevated" or "Not Elevated") directly against the CT scan ground truth, without measuring the impact of a human healthcare professional's subsequent decision-making. The device provides "a semiquantitative interpretation of test results derived from these measurements," which is then used "in conjunction with other clinical information, to aid in the evaluation of patients...to assist in determining the need for a CT scan." So, while it's an aid to a human, the performance metrics reported are for the device's output itself.

7. The Type of Ground Truth Used

The primary ground truth used for the clinical studies was the presence or absence of acute traumatic intracranial lesions visualized on a head CT (Computed Tomography) scan. This ground truth was established by consensus interpretation of neuroradiologists.

8. The Sample Size for the Training Set

• Assay Cutoff Determination: A training set of 420 subjects (274 males and 146 females) with suspected mild TBI was used to determine the assay cutoffs for GFAP and UCH-L1.

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

For the 420 subjects in the training set used to establish assay cutoffs:

• Subjects had suspected mild traumatic brain injury (Glasgow Coma Scale score of 13-15).
• Blood was drawn within 12 hours of injury.
• A head CT scan determination was performed.
• The ground truth would have been established by the head CT scan results (presence or absence of acute traumatic intracranial lesions), similar to the clinical study's ground truth, though the specific process of expert review for these 420 cases is not detailed beyond "head CT scan determination." It's reasonable to infer a similar process of expert radiologist interpretation.

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