Prognostic value of neuropeptide proenkephalin A in patients with severe traumatic brain injury.

High plasma proenkephalin A levels have been associated with poor clinical outcome of aneurysmal subarachnoid hemorrhage. This prospective observatory study was designed to investigate the relationship between plasma proenkephalin A levels and 1-week mortality, 6-month mortality and 6-month unfavorable outcome (defined as Glasgow Outcome Scale score of 1-3) in patients with severe traumatic brain injury. This study recruited 128 patients and 128 sex- and age-matched healthy controls. Plasma proenkephalin A levels, as measured by chemoluminescence sandwich immunoassay, were statistically significantly higher in patients than in healthy controls (239.1±93.0 pmol/L vs.81.3±22.1 pmol/L; P<0.001) and were correlated with Glasgow Coma Scale scores (r=-0.540, P<0.001). It was identified as an independent prognostic predictor of 1-week mortality [odds ratio (OR), 1.214; 95% confidence interval (CI), 1.103-1.425; P<0.001], 6-month mortality (OR, 1.162; 95% CI, 1.101-1.372; P<0.001) and 6-month unfavorable outcome (OR, 1.116; 95% CI, 1.097-1.281; P<0.001). Moreover, it had high predictive value for 1-week mortality [area under curve (AUC), 0.852; 95% CI, 0.778-0.908], 6-month mortality (AUC, 0.841; 95% CI, 0.766-0.899) and 6-month unfavorable outcome (AUC, 0.830; 95% CI, 0.754-0.891). Furthermore, its predictive value was similar to Glasgow Coma Scale score's (all P>0.05). Yet, a combined logistic-regression model did not show that it statistically significantly improved the predictive value of Glasgow Coma Scale score (all P>0.05). Thus, it was proposed that enhanced plasma proenkephalin A could be a useful, complementary tool to predict short- or long-term clinical outcome after severe traumatic brain injury.