Comparability of GFAP and UCH-L1 Measurements Using Handheld and Core Laboratory TBI Plasma Tests and Their Diagnostic Performance for Traumatic Intracranial Lesions

BACKGROUND: Glial fibrillary acidic protein (GFAP) and ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) are cleared by the U.S. Food and Drug Administration (FDA) to aid computed tomography (CT) decision-making in patients with traumatic brain injury (TBI). Two commercial assays, i-STAT TBI Plasma test and Alinity i TBI test, quantify these biomarkers using distinct detection technologies. Limited comparative data exist, creating uncertainty about cross-platform agreement and interchangeability of results in clinical and research applications. METHODS: GFAP and UCH-L1 concentrations were measured twice from 829 adults who underwent brain CT within 24 h of blunt trauma, first using the Abbott i-STAT TBI Plasma test and second using the Alinity i TBI test. Agreement was assessed using percent agreement (binary outcomes), Bland-Altman plots, Passing-Bablok regression, and Pearson correlation, with and without imputed values for out-of-range results. Diagnostic accuracy for traumatic intracranial lesions (tICLs) was calculated at assay-specific cutoffs. RESULTS: For GFAP + UCH-L1 in combination, the overall cross-platform agreement was 92.28%. GFAP and UCH-L1 showed strong cross-platform correlations with imputed (r = 0.916 and 0.916, respectively) and non-imputed data (r = 0.942 and 0.909, respectively). Both tests detected all clinically significant tICLs, with sensitivities of 100% (95% CI, 89%-100%) and negative predictive value (NPV) of 100% (95% CI, 98%-100%). Specificities were 29% (95% CI, 26%-32%) for i-STAT and 25% (95% CI, 22%-28%) for Alinity i. CONCLUSIONS: GFAP and UCH-L1 showed strong cross-platform agreement, individually and in combination, with equivalent sensitivity for tICL, supporting clinical interchangeability of the binary positive/negative test results.