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The TBI test is a panel of in vitro diagnostic chemiluminescent microparticle immunoassays (CMIA) used for the quantitative measurements of glial fibrillary acidic protein (GFAP) and ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) in human plasma and serum and provides a semi-quantitative interpretation of test results derived from these measurements using the Alinity i system.

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 negative test result is associated with the absence of acute intracranial lesions visualized on a head CT scan.

The TBI test is intended for use in clinical laboratory settings by healthcare professionals.

The TBI test is a panel of in vitro diagnostic quantitative measurements of GFAP and UCH-L1 and provides a semi-quantitative interpretation of GFAP and UCH-L1 in human plasma and serum.

The GFAP assay (subject device) is an automated immunoassay for the quantitative measurement of GFAP in plasma and serum using chemiluminescent microparticle immunoassay (CMIA) technology on the Alinity i system.

The UCH-L1 assay (subject device) is an automated immunoassay for the quantitative measurement of UCH-L1 in plasma and serum using chemiluminescent microparticle immunoassay (CMIA) technology on the Alinity i system.

Here's a breakdown of the acceptance criteria and the study proving the device meets them, based on the provided FDA 510(k) summary for the Abbott Laboratories TBI test:

1. Table of Acceptance Criteria and Reported Device Performance

The acceptance criteria for the TBI test are implicitly defined by the clinical performance observed in the pivotal study, particularly regarding its ability to aid in determining the need for a head CT scan in patients with suspected mild TBI. The key performance metrics are Sensitivity and Negative Predictive Value (NPV) as these are critical for a rule-out test for a serious condition like intracranial lesions.

Study Proving Device Meets Acceptance Criteria:

The device's performance was proven through a combination of analytical studies and a pivotal clinical study, supplemented by a fresh specimen study.

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

• Pivotal Clinical Study (Archived Specimens):

  • Sample Size: 1899 subjects.
  • Data Provenance:
    • Country of origin: Specimens were collected in a prospective, multi-center clinical study across 22 clinical sites in three countries: United States, Germany, and Hungary.
    • Retrospective/Prospective: The original collection of specimens was prospective. The testing of these archived specimens for the TBI device was essentially a retrospective analysis of prospectively collected and archived samples.

• Supplemental Clinical Study (Fresh Specimens):

  • Sample Size: 97 subjects.
  • Data Provenance:
    • Country of origin: 5 clinical sites in the United States.
    • Retrospective/Prospective: Specimens were freshly collected and tested prospectively for this supplemental study.

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

• Number of Experts: At least two neuroradiologists for initial interpretation, with a third neuroradiologist for adjudication if necessary.
• Qualifications of Experts: Neuroradiologists who were masked to other clinical and laboratory data. The document does not specify years of experience for these neuroradiologists but implies their expertise through their specialization and role in interpretation.

4. Adjudication Method for the Test Set

• Method: Consensus interpretation between two neuroradiologists, with adjudication by a third neuroradiologist if necessary. This is commonly referred to as a 2+1 adjudication method.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study was done, and the effect size of how much human readers improve with AI vs without AI assistance.

• No, an MRMC comparative effectiveness study was not explicitly done in the context of comparing human readers with AI assistance versus without AI assistance.
• The TBI test is an in vitro diagnostic immunoassay that provides biomarker levels (GFAP and UCH-L1) and a semi-quantitative interpretation to aid in the evaluation of patients. It is not an AI algorithm designed to interpret medical images or directly assist human readers in image interpretation. Its output (positive/negative TBI interpretation) is intended to assist clinicians in deciding on the need for a CT scan, rather than enhancing a reader's performance in interpreting existing images.

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

• Yes, in a sense, the primary clinical performance evaluation is a "standalone" or "algorithm only" performance.
• The TBI test provides a semi-quantitative interpretation (Positive/Negative) based on the measured levels of GFAP and UCH-L1 (using predefined cutoffs). This interpretation is compared directly to the ground truth (adjudicated head CT scan results) to determine the device's diagnostic accuracy (sensitivity, specificity, NPV, PPV). There is no human intervention in the generation of the TBI interpretation itself or its comparison to the CT ground truth. Clinicians then use this objective test result, "in conjunction with other clinical information," to make decisions.

7. The Type of Ground Truth Used

• Type of Ground Truth: Adjudicated Head CT Scan Results.
• Specifically, the ground truth was based on the presence or absence of "acute intracranial lesions visualized on a head CT scan." This involved both the imaging data itself and expert interpretation and consensus.

8. The Sample Size for the Training Set

• Sample Size: The assay cutoffs were determined using a training set of 354 subjects.
  • This training set included 132 CT positive subjects with suspected mild TBI.

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

• The training set subjects also had their ground truth established by a head CT scan determination, similar to the test set.
• The document implies that these CT scans were used to identify subjects as "CT positive" (presence of acute intracranial lesions) or "CT negative" (absence of acute intracranial lesions).
• The process for establishing the ground truth for the training set likely followed the same methodology as the test set: performed per the clinical site's standard of care, interpreted by neuroradiologists, and adjudicated for consensus on the presence or absence of acute intracranial lesions.

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