This study identified serum D-dimer level ≤ 2.5 µg/mL as predictive of isolated injury that could be detected with selected-region rather than whole-body CT; the model had a high specificity and high PPV. Similarly, the same cutoff value for D-dimer level had > 95% specificity and PPV for isolated non-severe injury. In this study, almost one-third of the patients had serum D-dimer levels below this cutoff, suggesting that using this threshold could spare a considerable number of patients from undergoing whole-body CT.
Serum D-dimer level measured immediately after trauma has been previously suggested as a marker indicative of injury severity. A recent retrospective study reported that serum D-dimer level was associated with injury severity and unfavorable clinical outcomes in trauma patients [8, 10–11]. Moreover, other studies have shown that serum D-dimer levels were associated with the number of fractures and mild traumatic brain injury detected by CT [12–13]. In addition, pathophysiological studies have found that endothelial damage due to blunt trauma triggered coagulation and enhanced fibrinolysis, resulting in elevated serum D-dimer levels . Furthermore, it has been suggested that tissue hypoperfusion caused by injuries leads to the acute release of t-PA from endothelial cells; thus, the degree of increment in serum D-dimer level would be related to the extent of injured sites . In the present study, D-dimer level was indicative of isolated injury, suggesting its suitability as a candidate marker for determining the necessity of whole-body CT.
Exposure to radiation associated with whole-body CT is a concern in trauma care worldwide. A recent retrospective study aimed to develop a prediction model that could reduce the number of unnecessary whole-body CT scans among trauma patients . Although the proposed model had a high sensitivity for multiple injuries with AIS score > 1 or single injuries with AIS score > 2, it required the input of several other variables, including injury mechanism, number of injury sites, and details of vital signs. Meanwhile, a prospective observational study concluded that physician judgement based on patient history and/or physical examination, including vital signs, is insufficient to determine the necessity of hole-body CT . In contrast, the model presented in the present study is based solely on serum D-dimer levels that predict isolated injury, which can be confirmed by selected-region CT; this model can be easily applied in trauma centers worldwide. Notably, point-of-care tests for serum D-dimer levels have been developed and are available to physicians; using these tests, D-dimer levels can be determined within 10 min after hospital arrival .
The specificity of serum D-dimer level cutoff value presented in this study is similar to that in other validated screening tests used in emergency settings, such as rapid influenza virus antigen test or troponin T test for myocardial infarction [19–20]. These tests, which have 98% specificity, have been used as reliable qualitative indicators in urgent care, suggesting that serum D-dimer levels ≤ 2.5 µg/mL, with a similar specificity value, might be suitable for use in an emergency trauma setting. Finally, as approximately 30% of included patients satisfied this cutoff value, it is likely a useful parameter in the treatment of blunt trauma patients.
This study has some limitations, which should be considered when interpreting its findings. Although D-dimer level has a high specificity and high positive predictive value for isolated injury, the presented cutoff value was not validated with data from an independent cohort. Differences in study settings, including regional trauma system, trauma evaluation system at hospitals, and patient characteristics, likely limit the generalizability of our findings. Moreover, the proposed D-dimer level cutoff value can only help to exclude whole-body CT from the diagnostic process; however, it is not indicative of the regions that should targeted with selected-region CT, which may require vital sign analysis or physical examination.
Finally, due to the retrospective nature of this study, the presented findings are not conclusive. Unmeasured confounding factors, including comorbidities such as pulmonary embolism and deep venous thrombosis, can increase D-dimer levels, affecting the precision of the proposed model [21–22]. Prospective studies are required to evaluate the utility and predictive value of the proposed indicator.