GFAP/UCH-L1 Assay for mTBI: Preanalytical Factors and Levels in Healthy Individuals-A Study on Danish Adults

Ubiquitin C-terminal hydrolase-L1 (UCH-L1) and glial fibrillary acidic protein (GFAP) have been evaluated as an alternative to S100 calcium binding protein B (S100B), which is mentioned in the Scandinavian guideline for managing mild traumatic brain injury (mTBI). Preanalytical, analytical and diagnostic performance of GFAP/UCH-L1 must be assessed before clinical use.

GFAP/UCH-L1 were quantified using the TBI assay on Abbott Alinity. Precision was estimated using internal quality controls, and matrix effects were evaluated using serum and plasma from 30 outpatients. Repeatability and stability at different conditions (25, 4, -20, and -80°C) were evaluated on serum and plasma. GFAP and UCH-L1 serum levels in 30 healthy individuals were determined and compared to S100B levels.

Inter-instrumental precision was ≤4.2% for both biomarkers. Random outliers were observed for UCH-L1 in plasma, where 5 measurements deviated >25%. Acceptable storage stability was found for GFAP and UCH-L1. All healthy individuals had GFAP values within the manufacturer's reference interval (6.6 to 70.9 ng/L) and two exceeded the upper limit for UCH-L1 (44.7 to 226.8 ng/L). Four healthy individuals (13%) had GFAP results above cutoff without S100B exceeding its cutoff, while one individual had values of S100B above cutoff but GFAP below cutoff.

The analytical precision and storage conditions of GFAP/UCH-L1 were satisfactory. Serum and plasma can be used for measurement of GFAP, whereas UCH-L1 measurement in plasma is not advised until further evaluations are conducted. The manufacturer's upper reference limits may not be suitable for our population. Thorough research on cutoff values is necessary.