BIOMARKERS OF HEAD INJURY Specification for
constituent assay results GFAP and UCH-L1
below (<) cut-off
GFAP and/or UCH-L1 above (≥) cut-off
1 Positive
Potential reduction in unnecessary CT scans (specificity)
Table 1. Traumatic brain injury test interpretation.
or older who presented to a healthcare facility or emergency department (ED) with head injuries and GCS scores of 9–15. Only mild TBI patients (GCS 13–15) were included in the pivotal study analysis.
Subjects had blood drawn within 12 hours of head injury, and TBI assessment was determined using CT scan, as well as demographic and medical history information for each subject at the time of enrolment. Computed tomography scans were performed in accordance with the clinical site’s standard of care. Based on the CT scan outcomes, cases were identified as CT-positive or CT- negative as defined by the presence or absence of acute traumatic intracranial lesions, respectively. Acute intracranial lesion was defined as any finding visualised on the scan induced by or related to trauma. Levels of GFAP and UCH-L1 were
measured in plasma samples using the Alinity i TBI test. Negative and positive results were defined according to the automated interpretation relative to the respective cut-off values shown in Table 1.
Pivotal results Among the 1899 mild TBI patients (TBI– CT–) / (CT-) Table 2. Clinical performance of the TBI test in the pivotal study.
included in the pivotal study analysis, 120 were identified as CT-positive. The TBI test identified these patients with a sensitivity of 96.7% (116/120 cases). None of the four CT-positive patients with a negative TBI test result were identified to have lesions requiring surgical intervention.2
Five subjects in the study were identified with lesions requiring surgical intervention; none of these had a false-negative result, suggesting that the TBI test correctly classified all five CT-positive subjects with a positive TBI interpretation.
Overall, the TBI test was negative in 717 patients, among which 713 were CT-negative. Hence, the negative predictive value (NPV) of the test was 99.4%. High sensitivity and NPV support the clinical utility of the test to assist in determining the need for a CT scan,2
as
high NPV gives the clinician confidence that a negative result indicates a true negative test.3
Distribution of CT scan
and TBI test results in the pivotal study are shown in Figure 1. As 713 cases were correctly identified as negative by the TBI test, the potential benefit of the assay would be a reduction in unnecessary CT scans by approximately 40%
(40.1%; 713/1779 subjects had true negative assay results). Table 2 shows calculations of all clinical performance parameters.
References 1 Alinity i TBI H22974R01. Instructions
for use. Sligo, Ireland: Abbott Ireland Diagnostics Division, October 2021.
2 GFAP (8100/04W17) & UCH-L1 (8100/04W19) for use with Alinity i. Alinity i TBI Design Validation Record_V3.
3 Umberger RA, Hatfield LA, Speck PM. Understanding negative predictive value of diagnostic tests used in clinical practice. Dimens Crit Care Nurs 2017; 36 (1): 22–9. doi: 10.1097/DCC.0000000000000219.
A White Paper produced by The Economist Intelligence Unit [TBI EIU Whitepaper | Core Laboratory at Abbott (
diagnostics.abbott)] provides more information about the potential of blood-based biomarkers to improve the evaluation and management of TBI.
Further information on the TBI immunoassay is available online:
www.corelaboratory.abbott/int/en/ offerings/segments/neurology/mild- traumatic-brain-injury
Alinity i TBI and Alinity are trademarks of Abbott 713/1779 40.1% TBI result TBI interpretation Sensitivity 0 Negative NPV Rate of false negatives among CT+ (CT– TBI–) / (TBI–) (TBI– CT+) / (CT+) 713/717 4/120 99.4% 3.3% Formula (TBI+ CT+) / (CT+) Calculation 116/120 Result 96.7%
(Green sector not visible due to small size) Includes five cases requiring neurosurgical intervention
Potential reduction in unnecessary CT scans
CT+; TBI test+ CT+; TBI test–
Fig 1. Computed tomography scan and TBI test results in the pivotal study.
WWW.PATHOLOGYINPRACTICE.COM SEPTEMBER 2022 39
CT–; TBI test+ CT–; TBI test–
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