CJSM May 2021 Journal Club — Blood Biomarkers in Pediatric Concussions

The May 2021 CJSM issue has just published, and as always it is full of articles you will want to read.

As I gaze at the table of contents, a non-random sampling of eye catching articles includes

CJSM Junior Associate Editor Jason Zaremski, MD breaks it all down for us.


Clinical Journal of Sports Medicine

Online Journal Club May 2021

CJSM Junior Associate Editor Jason Zaremski, MD

Jason L Zaremski, MD, CAQSM, FACSM, FAAPMR

Anzalone AJ, et al. Blood Biomarkers of Sports-Related Concussion in Pediatric Athletes.

Introduction:  There has been a substantial amount of interest in the diagnosis, evaluation, and management sports related concussions (SRC) in the past decade. An emerging area of interest has been the study of biomarkers as a more objective measure of head trauma. Two blood biomarkers — Neurofilament light polypeptide (Nf-L), primarily found in axons, and Tau, a microtubule-associated protein necessary for axonal transport — have been studied at advanced level of sport (collegiate, professional, and Olympic athletes).

The authors of this new study evaluated these blood biomarkers in pediatric athletes.  The main outcome measures they looked at were correlations between self-reported symptom measures biomarker concentration levels.

Purpose/Specific Aims: The authors examined patterns of blood biomarker concentrations (tau and Nf-L) in pediatric athletes seen in clinic in the days following a SRC and at a six-month follow up.  A comparator group of non-injured controls were assessed as well.  Correlations between biomarker concentrations and self-reported symptom scores were assessed.

Setting: Outpatient clinical setting

Methods/Design: Prospective Cohort Study including injured (SRC) and non-injured (control) athletes. Athletes provided a blood sample at initial evaluation and at 6 months post injury. Non-athletes provided one blood sample. Data were collected between August 2015 and December 2016. Pre-study approval was granted by an institutional review board. Informed consent and assent were obtained from all participants and (if less than 18 years old) parent(s) or legal-guardian consent. The 6-month follow-up only commenced if the athlete successfully returned to sport with no additional significant head trauma in the interim.

Participants:  Athletes 13 to 18 years old (15.1 ± 1.4 (12-18)), 66% male, 50% American football players, with a diagnosis of a SRC confirmed by a physician or physician assistant. The comparison group of non-injured athletes with no history of concussion ages 13-23 years old (19.2 ± 2.2 (13-23)), 40% male, recruited from all competitive sports from local high schools and universities.

SRC Group: N = 92 who provided a post injury sample, though 97 were initially enrolled. N = 20 returned 6 months after injury. The most common SRC related symptoms included headache, difficulty concentrating, and light sensitivity. See table 1 for further details.

Inclusion Criteria SRC Group: Assessment performed within 1-7 days of sustaining a SRC with a planned return to sport once cleared.

Exclusion Criteria SRC Group:  No history of brain surgery, ophthalmic surgery, and/or TBI graded more severe than concussion. Also, those that failed the graduated RTP protocol and underwent clinical reevaluation were excluded from the current study.

Non-Concussed Athlete Group: N = 30.

Inclusion Criteria Non-Athlete Group No history of concussion, brain injury, brain surgery, or ophthalmic surgery. Further, no current participation in sport.

Data Collection Design and Protocols: Before all clinic appointments, participants were advised to cease all physical and sport-related activities. Basic data collection included demographics, medical and injury history, recovery duration, and post-concussion symptom reports. Symptom reporting was collected using a post-concussion symptom scale (PCSS). Of note, the PCSS that was in use at this sports concussion clinic was developed by the clinicians at the clinic and uses a 7-point rating scale ranging from zero, indicating that the symptom is not present, to 6, indicating a “severe” degree of the symptom.

Recovery was defined as the period that elapsed between the initial injury and the initiation of the graduated return to play (RTP) protocol (which began only after an athlete remained symptom free for a minimum of 48 hours, displayed a normal physical examination, and achieved neurocognitive testing scores at athlete’s baseline).

Blood Collection: Non-fasting blood samples were collected via venipuncture.  Serum samples clotted for 30 minutes at room temperature and were then centrifuged. Plasma samples were centrifuged within 20 minutes of collection. All samples were aliquoted and stored at -80°C for future analyses.

Biomarker Analysis and Quantification: Plasma tau and serum Nf-L concentrations were measured using digital array technology on a Single Molecule Array HD-1 Analyzer. The same lot of kits was used for each assay.

All samples were above the lower limit of quantification (tau, 0.061 pg/mL; Nf-L, 0.171 pg/mL). The lower limit of detection was 0.007 and 0.055 pg/mL for tau and Nf-L, respectively. Duplicates were run with a median dose coefficient of variation of 3% for tau and 6% for Nf-L.

Statistical Measures/Analysis:  Summarizing from the manuscript: statistical significance was established at P<0.05. Statistical analyses were performed using the statistical Package for Social Sciences (SPSS Version 24.0). Graphs were created using GraphPad Prism 7. Mean and SD for continuous variables were calculated, and frequency distribution for categorical variables was calculated. Concussed athletes were categorized into 3 groups: loss of consciousness (LOC), normal recovery (≤28 days), and prolonged recovery (>28 days).

The normality assumption for continuous data was evaluated using the Shapiro–Wilk test. Chi-squared tests were used to compare proportion of patients with symptoms between the SRC and non-athlete groups. Spearman rank correlation coefficients were used to determine the relationship between biomarkers and clinical outcome measures: number of symptoms reported, total PCSS score (sum of all symptom scores), and recovery time.

Results Summary:


12 (9.8%) concussed athletes experienced LOC, 63 (51.6%) and 17 (13.9%) experienced normal (≤28 days) and prolonged (>28 days) recoveries, respectively.

The highest values of tau were observed in those reported within 1 day of injury, although the difference between those levels and controls was nonsignificant. The tau concentrations were lower in those athletes presenting on days 2-7. The highest values of Nf-L were documented in those athletes reporting on the seventh day after injury, which approached significance when compared with non-concussed control athletes.

Blood Bio-Marker Results Summary:

  • tau: Significantly lower for SRC compared with non-athletes
  • Nf-L: Higher for SRC compared to non-athletes (non-significant)
  • Plasma Tau: Significantly lower postinjury compared to 6 months after SRC
  • Serum Nf-L: Significantly higher postinjury.
  • tau and Number of SRC Symptoms: Inverse relationship (significant)
  • Nf-L and Number of SRC Symptoms: No relationship


  • Methodology well designed
  • Focused niche of patients (SRC pediatric age group)
  • Adds to a burgeoning area of research needed for our younger population

Weaknesses & Limitations:

  • Not ready for clinical utility.
  • Utility of blood biomarkers for SRC currently is not efficient or cost-effective. In fact, the authors state that previous data has indicated that elevations in plasma tau are observed within 1 to 6 hours of SRC and returning to baseline within a few days.
  • Table 1 uses n = 97, not 92 for the SRC cohort that completed the study. This could have altered the data slightly.
    • Further, when adding up the total number of sports played by participants (in table 1) as well as the number of biomarker participants in SRC cohort this equals 92, not 97.
  • 3% non-concussed cohort participated in non-contact sports as opposed to only 13% of the SRC
  • High lost to follow-up number (only 21.7% of SRC cohort failed to return for the 6-month follow-up visit, 20 out of 92).
  • The groups should be more closely matched for similar characteristics.
  • The average ages of each cohort were different by more than 4 years, which could be considered a large difference in a study of adolescents
    • Further, the comparison group with a mean of 19.1 years old (with some included > 21 years old) many might not agree this is a “pediatric” group.
  • It would be interesting to note if there were differences in the blood biomarkers between sexes
  • I am not clear under exclusion criteria what “TBI graded more severe than concussion” means. I suspect the authors were attempting to state that the SRC sustained did not result in hospital admission and/or may be called a “mild” TBI.
  • I am curious why the SRC participants that failed the graduated RTP protocol and underwent clinical reevaluation were excluded from the current study. Would they not provide some insight with their blood biomarkers that could potentially explain why they failed the RTP protocol?
  • The PCSS used in standard concussion assessments (and approved by the Berlin Consensus Statement) was not used.
  • The recovery definition is not in line with the standard expert recommendation. Initiating a RTP protocol only after an athlete has remained symptom free for 48 hours is not necessarily the standard. The consensus for RTP is asymptomatic with a normal physical examination and has participated in a return to play program, but without a specific time frame. (https://www.cdc.gov/headsup/basics/return_to_sports.html; McCrory, Paul, et al. https://bjsm.bmj.com/content/51/11/838.) As stated in the Consensus statement on concussion in sport—the 5th international conference on concussion in sport held in Berlin, October 2016:
    • After a brief period of rest during the acute phase (24–48 hours) after injury, patients can be encouraged to become gradually and progressively more active while staying below their cognitive and physical symptom-exacerbation thresholds (ie, activity level should not bring on or worsen their symptoms). It is reasonable for athletes to avoid vigorous exertion while they are recovering. The exact amount and duration of rest is not yet well defined in the literature and requires further study.”

Conclusions:  After sustaining an SRC, the blood biomarkers tau and Nf-L do not appear to have a relationship to SRC symptoms in pediatric athletes.

Clinical Relevance:  As the authors state, identifying blood biomarkers as part of a concussion diagnostic tool may provide additional data to assist in management and treatment of a SRC. However, at this time, further research is required.

About sportingjim
I work at Nationwide Children's Hospital in Columbus, Ohio USA, where I am a specialist in pediatric sports medicine. My academic appointment as an Associate Professor of Pediatrics is through Ohio State University. I am a public health advocate for kids' health and safety. I am also the Deputy Editor for the Clinical Journal of Sport Medicine.

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