Traumatic brain injury (TBI) remains a major cause of death and disability. TBI is presented as a heterogeneous array of pathologies and severities [
1]. This creates a significant challenge to the health providers, who take care of head injured patients, when attempting to identify and classify the patients that may benefit from a certain management. Currently, the basic classification of TBI patients is based on neurological injury severity criteria with the Glasgow Coma Scale (GCS) being the most commonly used scale for prognostic and follow-up evaluations, and to enroll patients into clinical trials [
2‐
5]. In recent years, the traditional link between GCS and outcome has been questioned, and published data suggest that the predictive value of GCS should be reconsidered [
6]. The Marshall [
7] and the Rotterdam [
8] scores for CT findings are the best known classification systems based on pathoanatomic features of the injury. Despite becoming widely used and serving as pragmatic tools, the CT-based classifications are not free of limitations [
9]. To overcome the inherited drawbacks of the aforementioned clinical and pathoanatomic methods the role of biomarkers has been studied with S100, neuron-specific enolase, and Hsp 70 being among the most widely investigated [
10‐
12]. However, failure to demonstrate adequate sensitivity and specificity prevented their routine clinical use as diagnostic or prognostic tools. Accumulative data favored the potential use of circulating cell-free DNA (CFD) in the plasma or serum for diagnosis, prognosis, and monitoring of a variety of conditions such as infection, inflammation, trauma, in critically ill patients with respiratory insufficiency or pulmonary embolism, in patients with autoimmune diseases, sepsis and cancer [
13‐
19]. Pioneering studies explored the potential role of CFD as a surrogate biomarker in the management of TBI. Campello et al. demonstrated that severe TBI is associated with elevated CFD and that persistent increased concentrations of CFD correlate with mortality [
20]. Macher et al. also showed that severe TBI is associated with augmented CFD levels, and suggested that early (within 24 hours) CFD concentrations decrease predicts a better outcome [
21]. Despite these initial promising results on the value of CFD measurement in TBI patients this scheme has not yet entered into clinical use. A major obstacle is the applicability of the methods used to measure CFD. The currently available research methods for CFD measurement are work-intensive and expensive, requiring DNA extraction and real-time polymerase chain reaction amplification with specific primers. We recently developed a convenient DNA assay applied directly to biologic samples. This assay uses the fluorochrome SYBR Gold (Invitrogen, Paisley, Scotland), which does not require prior processing of samples. The assay is simply performed by adding diluted fluorochrome to the samples and measurement of fluorescence. The assay was proved to be accurate, sensitive, reproducible, cheap and rapid [
22]. In a previous study, researchers from our institution found that CFD levels correlated with brain damage and with the neurological outcome after TBI in a rat model [
23]. The aim of the present study was to evaluate this method for the identification of CFD in TBI patients, and whether it may serve as an additional diagnostic and prognostic tool capable to assist in the management of head injured patients. We hypothesized that CFD concentrations would associate with severity of injury, and that low or high levels could differentiate between good or bad outcome, respectively.