ABSTRACT NUMBER: ESOC2026A2048 PREHOSPITAL RULE-IN AND RULE-OUT OF INTRACRANIAL HEMORRHAGE WITH SINGLE-TIMEPOINT GFAP MEASUREMENT

Abstract Background and aims Glial fibrillary acidic protein (GFAP) is a leading biomarker candidate for prehospital differential diagnosis of acute stroke code patients. We explored the diagnostic capability of prehospital GFAP to rule-in and rule-out intracranial hemorrhage (ICrH) in a large cohort of acute stroke code patients, optimizing cut-offs to provide high diagnostic certainty. Methods Laboratory measurement of GFAP was performed with Alphalisa® in plasma samples collected <6 hours of symptom onset, with a median (IQR) last-known-well to sampling time of 60 (38-107) minutes. ICrH rule-in and rule-out cut-off values were selected separately for each sex and age group (male <60, 60-75, >75 years, female <60, 60-75, >75 years). Results We included 938 patients (122 ICrH, 615 acute cerebral ischemia [ACI], 201 stroke mimic [SM]). With rule-out cut-offs, GFAP ruled out ICrH with high certainty (NPV 98.1%) in 479 patients (51.1% of the cohort, 57.6% of ACI/SM patients), with 9 false negative cases (patients with very small hematoma volume). With rule-in cut-offs, GFAP diagnosed ICrH with moderate certainty (PPV 88.9%) in 36 patients (3.8% of the cohort, 26.2% of ICrH patients), with 4 false positive cases. Overall, 423 (45.1%) were left in-between rule-out and rule-in cut-offs in a diagnostic gray area. Conclusions In the ultra-early differential diagnosis of stroke code patients, prehospital plasma GFAP and high-certainty cut-offs correctly diagnosed 53.5%, incorrectly diagnosed 1.4% and left 45.1% undiagnosed. While single-timepoint GFAP has potential to provide significant improvement to prehospital diagnostics currently lacking in regular EMS units, adjunct diagnostic methods will be needed. Conflict of interest All authors: nothing to disclose