Elderly patients, defined as patients older than 65 years of age, with mild traumatic brain injury (mTBI) (Glasgow Coma Scale (GCS) of 13–15) represent a large proportion of patients visiting the Emergency Department (ED) [1], [2], [3]. Furthermore, patients 65 years of age or older have the highest rates of both TBI-related hospitalization and deaths [1]. It is an increasing public health concern as the elderly population continues to grow.

Among elderly patients who visit the ED with mTBI, 11–21 % show intracranial traumatic lesions, compared to 5–10 % in younger adults [4], [5], [6], [7]. Even elderly patients with a normal neurological examination are at risk of having an intracranial abnormality. Studies reported that up to 17 % of older adults presenting with mTBI and a GCS of 15 may have evidence of traumatic intracranial lesions on head computerized tomography (CT) [4,5].

Head CT is the most widely used diagnostic test in the evaluation of acute head and brain trauma when imaging is indicated by a validated clinical decision rule. However, most of these decision rules have defined age over 60 or 65 years as a major risk factor for intracranial Injury [5,[8], [9], [10]]. Thus, nearly all elderly patients who visit the ED with mTBI receive a head CT. There is a need to identify a diagnostic blood biomarker as an adjunct to clinical decision rules to detect intracranial injury in elderly after mTBI to reduce expensive and time-consuming head CTs [5,[8], [9], [10]].

The best-studied TBI biomarker is S100B, a calcium-binding protein which is located predominantly in the cytoplasm and nucleus of astrocytes and Schwann cells, but also in melanocytes, chondrocytes, adipocytes, and skeletal muscle. It is released in the bloodstream by damaged glial cells when the blood-brain barrier is disrupted [11]. Several studies have acknowledged the use of S100B for identifying patients who do not require a head CT after mTBI [12], [13], [14], [15], [16]. Due to a very high sensitivity and negative predictive value to detect traumatic intracranial hemorrhage, it has been incorporated into the Scandinavian Neurotrauma Committee (SNC) guidelines [10]. The addition of S100B as a screening test to these guidelines reduced the number of CT scans among adults by one-third, with a significant reduction in costs of care [17].

The role of S100B in the initial management of elderly with mTBI is still ill-defined. A few studies demonstrated that blood-based mTBI biomarkers exhibit equivalent predictive sensitivity between mTBI patients younger and over 65 years of age, but reduced specificity [18,19]. The process of human ageing and comorbid conditions might affect biomarker production, distribution, metabolism, and clearance resulting in different biomarker levels [20], [21], [22]. This is of importance when predicting outcome from mTBI in elderly patients, as higher blood levels may be falsely interpreted as elevated, resulting in the performance of unnecessary CT scans, even if few lesions are missed. We conducted this posthoc analysis on a recent published study [23] to better understand the influence of ageing on the predictive performance of S100B. The aim was to evaluate the predictive performance of S100B in patients older than 65 years of age with mTBI for detection of traumatic intracranial lesions. To substantiate our results, we also performed a systematic review and meta-analysis to evaluate the existing body of evidence for the use of S100B for the diagnosis of traumatic intracranial lesions on CT following mTBI in elderly patients.