Age-Adjusted Cut-Off Values for Glial Fibrillary Acidic Protein and Ubiquitin Carboxy-Terminal Hydrolase L1 Improve the Diagnostic Accuracy of the Abbott Mild Traumatic Brain Injury Assay

<b>Objectives</b>: To establish age-adjusted cut-off values for glial fibrillary acidic protein (GFAP) and ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) and assess their impact on the diagnostic performance of the mild traumatic brain injury (mTBI) assay. <b>Methods</b>: The study included 175 adult mTBI patients presenting at the emergency department (ED) within 12 h from head trauma in whom head CT scan was performed. GFAP and UCH-L1 were measured using chemiluminescence immunoassays on an Abbott analyzer (Abbott Laboratories, USA). <b>Results</b>: Using manufacturer's defined cut-offs (GFAP < 35 ng/L, UCH-L1 < 400 ng/L), the mTBI assay exhibited diagnostic sensitivity (Se) of 93.1%, specificity (Sp) of 28.8%, negative predictive value (NPV) of 95.5% and a positive predictive value (PPV) of 20.6%. In the subgroup of patients aged under 50, Se and NPV were below 100% (i.e., 75.0% and 92.3%), due to two false negative mTBI results. Age-adjusted cut-offs were defined for three patient groups, ≤49 years, 50-69 years and ≥70 years, and were set to 22.4, 37.0 and 62.3 ng/L for GFAP, and 349.3, 351.6 and 369.0 ng/L for UCH-L1. Using these cut-offs, in all patient groups Se and NPV were 100%, while increased Sp was obtained in patients older than 50 years. <b>Conclusions</b>: Diagnostic Se and NPV can be improved by the use of age-adjusted cut-offs. In this way, the triage protocol for mTBI and head CT scan can be refined, further contributing to the optimization of the diagnostic management of mTBI patients at the ED.