Cranial Cooling · Measurement
Clinical Exhibit: Blood-Based Biomarkers
Rationale, evidentiary status, and integration with cognitive and exposure measures
- Fluid biomarkers add an objective, quantitative axis alongside symptoms and cognition — used as intermediate endpoints, not as a diagnosis of concussion.
- GFAP & UCH-L1 — acute markers; the basis of FDA-cleared testing that helps exclude CT-detectable injury.
- NfL — a delayed, persistent axonal-injury marker, suited to tracking cumulative and longer-term burden.
- Any use beyond the cleared indication — severity grading or recovery trending — is treated as exploratory.
Rationale
Sport-related concussion is predominantly a functional and metabolic disturbance; conventional structural imaging is, by design, insensitive to it. Symptom inventories and neurocognitive testing remain central but are effort- and state-dependent. Fluid biomarkers contribute an objective, quantitative axis to the measurement strategy, enabling injury to be characterized at the time of insult and, prospectively, across a recovery and exposure trajectory. The intent in this study is not to position any marker as a diagnostic of concussion, but to use validated analytes as objective intermediate endpoints alongside exposure quantification and cognitive assessment.
Analyte profiles
| Marker | Cellular source | Kinetics / window | Role in this study |
|---|---|---|---|
| GFAP | Astroglial | Rises within hours of injury; relatively early peak | Acute structural-injury signal; component of cleared CT-triage testing |
| UCH-L1 | Neuronal | Early release post-injury; short half-life | Acute signal, paired with GFAP in point-of-care assays |
| NfL | Axonal (cytoskeleton) | Delayed rise; persists over weeks; reflects ongoing axonal injury | Longitudinal axonal-injury and cumulative-burden marker |
Acute markers: GFAP and UCH-L1
GFAP (astroglial) and UCH-L1 (neuronal) rise rapidly following TBI and are the basis of FDA-cleared blood testing developed in the mild-TBI population. The cleared indication is acute: the high negative predictive value of a combined GFAP/UCH-L1 result supports excluding CT-detectable intracranial injury, reducing unnecessary imaging. Two points are material for interpretation in a concussion cohort. First, the cleared target is CT-relevant structural injury, not concussion per se; the majority of sport concussions are CT-negative, so a negative acute result does not exclude concussion. Second, the assay was validated for an acute triage decision, not for severity grading or longitudinal monitoring. Within this study, GFAP/UCH-L1 are therefore used as an acute, objective injury signal and as a means of delineating uncomplicated concussion from the structurally injured presentations that warrant escalation, with any quantitative trending treated as exploratory.
Longitudinal marker: NfL
Neurofilament light is a cytoskeletal axonal protein and a sensitive, quantitative index of neuro-axonal injury. Its kinetics differ usefully from the acute markers: levels rise in a delayed fashion and persist, making it better suited to tracking subacute and cumulative injury than to point-of-care triage. NfL is non-specific, with elevations in aging and diverse neurological disease, so it is interpreted as a measure of axonal injury burden rather than a concussion-specific signal. Its low circulating concentrations require high-sensitivity platforms (e.g., single-molecule array methods). In this study NfL anchors the longitudinal end of the biomarker timeline, complementing the acute GFAP/UCH-L1 signal and supporting the cumulative-burden hypothesis central to the long-term design.
Integration with cognitive and exposure measures
The biomarker axis is one of three measurement layers and is not intended to stand alone. Instrumented exposure monitoring quantifies dose; validated, FDA-cleared neurocognitive and balance platforms (e.g., ImPACT, Sway) quantify functional performance; and the biomarkers provide a biological injury signal at acute and longitudinal time points. Concordance across these axes strengthens inference, and discordance is itself informative, for example an objective biomarker or exposure signal in the absence of symptom report. This triangulation, rather than any single endpoint, is what allows the study to test whether an intervention alters the injury and recovery trajectory.
Evidentiary status
- Established: GFAP/UCH-L1 as acute markers with cleared utility for CT-triage in mild TBI; NfL as a sensitive quantitative marker of neuro-axonal injury.
- Plausible but not established: the value of these analytes for grading concussion severity, for longitudinal recovery monitoring, and for indexing cumulative subconcussive burden. These are study questions, not settled findings.
- Treated as exploratory: any use of an analyte outside its cleared indication, including quantitative trending of acute markers and biomarker-based intervention effects.
Prepared as background for study discussion. Named platforms are illustrative of suitable validated tools, not statements of partnership. Specific assays, platforms, kinetic parameters, and regulatory clearances should be verified against current manufacturer labeling and the primary literature before use; uses beyond a test's cleared indication are research applications.