Cerebrospinal fluid haemoglobin as a monitoring biomarker for secondary brain injury after aneurysmal subarachnoid haemorrhage: prospective international multicentre validation study (HeMoVal)

ObjectivesTo validate whether cerebrospinal fluid oxyhaemoglobin (CSF-Hb), measured from external ventricular or lumbar drains, is associated with secondary brain injury (SAH-SBI) after aneurysmal subarachnoid haemorrhage (aSAH), and to assess its value as a real-time monitoring biomarker. DesignPreregistered multicentre prospective observational cohort study. SettingEight neurosurgical tertiary centres in Switzerland, Germany, and Austria, between August 2021 and June 2024. Participants366 patients with aSAH (mean age 58 years; 65% women). Of these, 260 provided cerebrospinal fluid (CSF) samples via external ventricular drain (EVD; 2,467 samples, median 10 days per patient) and 66 via lumbar drain (LD; 379 samples, median 6 days). InterventionsDaily CSF samples were collected via EVD or LD from day 1 to day 14 after haemorrhage; no therapeutic interventions were tested. Main outcome measuresCSF-Hb and its metabolites were analysed post hoc in a blinded manner. The primary outcome was SAH-SBI, defined as a composite of angiographic vasospasm (aVSP), delayed cerebral ischaemia (DCI), and delayed ischaemic neurological deficits (DIND), assessed daily over 14 days. Secondary outcomes included temporal CSF-Hb profiles and associations with aneurysm location, haematoma volume, intraventricular haemorrhage, chronic hydrocephalus, and 3-month functional outcome. ResultsCSF-Hb showed a delayed peak pattern: concentrations were low after aSAH, rose to a maximum on day 10 (EVD-derived CSF-Hb median 11.3 {micro}M, IQR 2.64 to 25.90), and then declined. Larger haematoma volume (p<0.001) and intraventricular haemorrhage (p<0.001) were associated with higher EVD-derived CSF-Hb. SAH-SBI occurred in 209/366 patients (57%). Daily EVD-derived CSF-Hb showed no association with SAH-SBI (p=0.25) and only poor prognostic potential of same-day SAH-SBI (area under the curve 0.59, 95% confidence interval 0.56-0.63), with substantial between-centre heterogeneity. The oxidised haemoglobin metabolite methaemoglobin was positively associated with SAH-SBI (p=0.023; odds ratio 1.18 per log[{micro}M], 95% confidence interval 1.02-1.36). Acute-phase EVD-derived CSF-Hb correlated with chronic hydrocephalus (p=0.012) and poor 3-month functional outcome (p=0.008). Catheter-related infection rates were low (2.2%). ConclusionsIn this preregistered multicentre validation study, EVD-derived CSF-Hb did not perform as a robust real-time monitoring biomarker for SAH-SBI, showing limited same-day discrimination and substantial between-centre heterogeneity. These findings argue against clinical implementation of CSF-Hb point-measurement as a single-parameter biomarker. In contrast, CSF methaemoglobin remained consistently associated with SAH-SBI, supporting the mechanistic relevance of haemolysis-related pathways. Future work using the HeMoVal biobank will apply multi-marker, pathway-level analyses to define haemolysis-related biomarker signatures and provide a platform for robust external validation of future candidates. Study registrationClinicalTrials.gov NCT04998370; date of registration 10 August 2021. Summary BoxesO_ST_ABSWhat is already known on this topicC_ST_ABSO_LIPreclinical animal models link cell-free haemoglobin in cerebrospinal fluid (CSF-Hb) to secondary brain injury after aneurysmal subarachnoid haemorrhage (SAH-SBI). C_LIO_LIA single-centre study reported strong associations between daily external ventricular drain (EVD) derived CSF-Hb levels and SAH-SBI, and suggested a strong predictive potential(area under the curve 0.89). C_LIO_LICSF-Hb monitoring has therefore been proposed as a bedside biomarker, but it has not undergone multicentre validation. C_LI What this study addsO_LIIn a preregistered multicentre cohort of 366 patients from eight neurosurgical centres, once-daily EVD-derived CSF-Hb measurements showed poor same-day discrimination for SAH-SBI (area under the curve 0.59) and substantial between-centre heterogeneity. C_LIO_LIIn contrast, CSF methaemoglobin was consistently associated with SAH-SBI, and higher acute-phase CSF-Hb was related to chronic hydrocephalus and worse 3-month functional outcome. C_LIO_LIThese findings argue against routine adoption of CSF-Hb point-measurements as bedside single-analyte, while supporting haemolysis-related pathways as mechanistic targets. C_LI