Subarachnoid hemorrhage (SAH) is a high-risk cerebrovascular condition associated with substantial morbidity and mortality, caused by arterial or venous bleeding into the subarachnoid space due to trauma, aneurysm rupture, vascular malformations, bleeding disorders, brain tumors, or anticoagulant-related complications.1,2 The incidence is estimated to be 2–22 per 100,000 people, and 60% of the patients is between the age of 40 and 60.3 The most common cause of subarachnoid hemorrhage (SAH) is trauma, whereas ruptured cerebral aneurysm represents the leading cause of non-traumatic SAH. In this context, cerebral vasospasm constitutes the principal determinant of morbidity and mortality following aneurysmal SAH, despite the fact that its underlying pathophysiology and optimal therapeutic strategies remain incompletely understood.4 Although cerebral vasospasm is detected radiologically in up to 70% of patients, only 20–30% develop clinically significant vasospasm. Accordingly, prognosis in non-traumatic SAH is influenced by multiple interrelated factors, including the location and volume of hemorrhage, rebleeding, vasospasm, acute hydrocephalus, and the overall clinical course.5,6 Cerebral vasospasm starts on the 3rd day after SAH, peaks on the 6th and 8th days and lasts for 2–3 weeks.7 It is a clinical diagnosis, and digital subtraction angiography (DSA) remains the gold standard for its detection.8 Despite advances in clinical and radiological monitoring, the role of biochemical biomarkers in the follow-up of subarachnoid hemorrhage remains controversial, and there is still a need for reliable biomarkers.

Myelin basic protein (MBP) is the second most abundant protein in central nervous system (CNS) myelin after proteolipid protein and plays a crucial role in myelin sheath formation by oligodendrocytes.9 MBP is widely accepted as a biomarker of brain tissue injury in both traumatic and non-traumatic neurological conditions. Serum MBP levels increase in traumatic brain injury10 and have been shown to be elevated in cerebrospinal fluid in multiple sclerosis, benign and malignant intracranial tumors, central nervous system infections, and cerebrovascular disorders.11–13 In addition, serum MBP concentrations may rise significantly in cerebral injuries such as cerebrovascular accident, intracranial tumors, and head trauma.14 Importantly, elevated peripheral blood MBP levels after aneurysmal subarachnoid hemorrhage reflect the severity of brain parenchymal damage and have been associated with treatment outcomes.9

Ischaemia-modified albumin (IMA) is generated by a reduction in the metal-binding capacity of albumin under conditions of oxidative stress and tissue ischaemia and was initially described in acute ischaemic stroke.15 It is considered a non-specific biochemical marker reflecting ischaemia and oxidative stress. IMA has been widely used in the diagnosis and clinical assessment of various ischaemia-related conditions, including myocardial infarction, brain and spinal cord injuries, diabetes mellitus, pregnancy-related complications, gynaecological disorders, and other ischaemic pathologies.16 Elevated serum IMA levels have been observed in a wide range of ischaemia-related conditions, such as cardiovascular and cerebrovascular diseases, metabolic disorders, malignancies, infections, and peripheral vascular diseases.17–22

In our study, we aimed to obtain an insight on the correlation between MBP and IMA values in serum and CSF with radiological evaluation, neurological examination, vasospasm and clinical courses and outcome in patients with non-traumatic SAH.

This single-centre, prospective methodological study was conducted on twenty patients admitted to Karadeniz Technical University (KTU) Faculty of Medicine, Farabi Hospital, with a diagnosis of non-traumatic SAH. Patients with a history of traumatic SAH were excluded.

This study was approved by the Karadeniz Technical University Faculty of Medicine Scientific Research Ethics Committee (Institutional Review Board approval number 2022/174, dated 29/07/2022), and all procedures involving human participants were conducted in accordance with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Written informed consent was obtained from all individual participants included in the study.

M. Fisher score was recorded on day 1, and GCS, WFNS, and Hunt–Hess scores were assessed on days 1, 5, and 10. Serum and CSF levels of MBP and IMA were measured using ELISA (enzyme-linked immunosorbent assay) on the 1st, 5th and 10th days at the KTU Biochemistry Laboratory. Correlations were examined between biomarker levels, demographic data, hypertension, radiological and clinical scores, vasospasm, and GOS score at discharge.

Spontaneous SAH is a complex clinical condition associated with high early mortality and morbidity, with a clinical course that is particularly characterized by the development of vasospasm and delayed cerebral ischemia within the first 10 days. Secondary brain injury occurring during this period progresses through mechanisms such as neuroinflammation, microcirculatory dysfunction, oxidative stress, and disruption of blood–brain barrier integrity.

Biochemical biomarkers are widely used in the diagnosis, prognostic assessment, and outcome prediction of various neuropathological conditions.23,24 However, no specific biochemical biomarker is currently available for the monitoring of non-traumatic SAH patients or SAH-associated vasospasm. Therefore, monitoring early-phase biomarkers following SAH has gained increasing importance for predicting clinical deterioration and determining prognosis.

In the present study, the temporal changes in serum and CSF levels of MBP and IMA on days 1, 5, and 10 were evaluated, and the associations of these biomarkers with clinical scoring systems were investigated. Our findings indicate that MBP levels increased significantly in both serum and CSF from the early phase onward, whereas IMA levels did not show a significant change in serum but may be associated with clinical deterioration in CSF, particularly in the late phase. In addition, correlations between biomarker levels and functional outcome assessed by the GOS were examined, and a significant association was identified between CSF IMA levels measured on day 10 and GOS scores.

Serum MBP levels demonstrated a statistically significant increase from day 1 to day 10 (p<0.001). The observation that this increase was significant particularly between days 1–5 (p=0.005) and days 1–10 (p<0.001), while the change between days 5–10 did not reach statistical significance (p=0.246), suggests that serum MBP rises predominantly in the early period following SAH and that the rate of increase may subsequently enter a relative plateau phase.

Wasik et al. reported that peripheral blood MBP concentrations following aneurysmal SAH reflect the severity of brain parenchymal injury and are associated with treatment outcomes.9 Similarly, in a study by Thomas et al., comparisons of serum MBP levels in patients with intracranial pathologies versus those with spinal or peripheral nerve disorders demonstrated elevated serum MBP levels in intracranial pathologies, whereas no such increase was observed in patients with spinal or peripheral nerve involvement.14

In another study conducted by Hoyle et al., patients followed for spontaneous SAH exhibited progressively increasing preoperative serum MBP levels, which reached their peak on postoperative day 10.25 Furthermore, Zheng et al. reported higher serum MBP levels in spontaneous SAH patients who developed symptomatic vasospasm. Elevated serum MBP levels were also found to be associated with vasospasm and poor 6-month outcomes and were correlated with WFNS scores.26

Consistent with these previous studies, our findings demonstrate a gradual increase in serum MBP levels (overall temporal change: p<0.001). Importantly, our results suggest that serum MBP may serve as a valuable biomarker for detecting early-phase tissue injury following spontaneous SAH.

CSF MBP levels demonstrated a more pronounced and continuous increasing pattern. The change in CSF MBP levels between days 1, 5, and 10 was statistically significant (p<0.001), and all pairwise comparisons (days 1–5, 1–10, and 5–10) also showed statistical significance (day 1–5: p=0.003; day 1–10: p<0.001; day 5–10: p=0.013). These findings support the notion that MBP may act as a more direct and cumulative marker of injury within the CSF compartment.

In a study published by Vries et al., CSF MBP levels were evaluated in neurosurgical patients. CSF MBP levels were found to be significantly elevated in patients with intracranial hemorrhage secondary to aneurysm or arteriovenous malformation, whereas no significant elevation was observed in patients with benign intracranial pathologies.11 Similarly, Hirasma et al. investigated CSF MBP levels together with SAH extent, degree of cerebral infarction, and discharge outcomes, and suggested that CSF MBP may serve as a marker reflecting the severity of vasospasm-related brain injury.27

In our study, consistent with the literature, both serum and CSF MBP levels showed an increasing trend. However, when evaluated together with clinical scoring systems, no association was observed between CSF or serum MBP levels and clinical scores, except for a moderate positive correlation between day 1 serum MBP levels and the HHS scores (r=0.502, p=0.024). This may be explained by the lack of significant changes in GCS, HHS, and WFNS scores between days 1, 5, and 10 (all p>0.05), and the absence of a clear group-level clinical trend. Nevertheless, the significant increase in MBP levels in both serum and CSF suggests that clinical scoring systems may not always fully capture the dynamics of biological injury. In addition, factors such as sedation, mechanical ventilation, hemodynamic optimization, and other supportive intensive care interventions may reduce the variability of clinical scores.

Since MBP is one of the principal structural components of central nervous system myelin, increases in serum and CSF MBP levels may be interpreted as a biochemical reflection of myelin sheath and axonal involvement during secondary injury processes following SAH. From this perspective, MBP elevation may represent not only the primary effect of hemorrhage but also the cumulative burden of tissue injury resulting from secondary mechanisms, including blood–brain barrier disruption, inflammatory responses, and hypoperfusion.

IMA is a biomarker associated with ischemia and oxidative stress and reflects structural modifications of albumin. In intracranial pathologies, Gunduz et al. reported that serum IMA levels measured within the first 24h were higher in patients with acute cerebrovascular disease compared with healthy controls.24 Similarly, Han et al. demonstrated a marked elevation in serum IMA levels as early as 3h after the onset of acute cerebrovascular pathology.28

In a study by Elshony et al., serum fibulin-5 and IMA levels measured within the first hours after hospital admission were significantly higher in patients with ischemic stroke, intracerebral hemorrhage, and SAH compared with controls. Additionally, fibulin-5 and IMA levels showed positive correlations with ischemic lesion volume and hemorrhage/SAH severity.29

In our study, serum IMA levels did not show a statistically significant change between days 1, 5, and 10 (p=0.157); however, the mean values at all time points remained elevated. The lack of significant temporal variation in serum IMA levels may be related to concomitant clinical conditions that could influence the ischemic oxidative stress response, as well as intensive care-related factors such as sedation, mechanical ventilation, and the use of vasopressor agents for hemodynamic optimization.

Although IMA has been proposed as an early indicator of ischemia and oxidative stress, it has also been reported to increase in various systemic conditions other than cardiac ischemia, including sepsis, metabolic syndrome, and diabetes.16,17,19–22 Therefore, serum IMA levels should not be interpreted independently of the clinical context and should preferably be evaluated together with more compartment-specific measurements or other clinical parameters.

In our study, serum IMA was measured using an ELISA method and expressed in ng/mL. Therefore, direct comparisons with studies using the Albumin Cobalt Binding test, which typically reports results in U/mL, may not be appropriate. However, in the literature, Aydogan et al. measured serum IMA levels using ELISA in ng/mL in patients with acute ischemic stroke and found significantly higher median serum IMA levels compared with healthy controls. They also defined cut-off values of >58ng/mL for acute ischemic stroke diagnosis, >76.7ng/mL for stroke severity, and >65.4ng/mL for poor 3-month outcomes.30

Despite the absence of a significant temporal increase, the median serum IMA values measured on days 1, 5, and 10 (∼98–109ng/mL) are consistent with previous literature demonstrating elevated IMA levels in acute and ischemia-related processes such as SAH.

To the best of our knowledge, no previous studies have evaluated CSF IMA levels in patients with non-traumatic SAH. Since multiple systemic and clinical factors can influence serum IMA levels and affect the clinical oxidative stress response, we hypothesized that measuring IMA in CSF, as a more central nervous system-specific compartment, may better reflect the clinical course.

In our study, CSF IMA levels demonstrated an increasing trend; however, this change remained at borderline statistical significance (p=0.059). Despite the borderline temporal change, it is noteworthy that CSF IMA showed significant correlations with clinical scores, particularly on day 10. A moderate negative correlation was observed between day 10 CSF IMA levels and day 10 GCS scores (r=−0.507, p=0.022), whereas a moderate positive correlation was found between day 10 CSF IMA levels and day 10 WFNS scores (r=0.457, p=0.043). These findings suggest that CSF IMA may be more closely associated with late-phase clinical deterioration following SAH.

This observation is consistent with the hypothesis that ischemic and oxidative stress burden within the CSF compartment may increase during the period when vasospasm and delayed ischemic injury risk become more prominent in spontaneous SAH patients (approximately days 7–10).

An important strength of our study is that correlation analyses were evaluated separately for each time point. The identification of a moderate positive correlation between day 1 serum MBP levels and day 1 HHS scores (r=0.502, p=0.024) suggests that MBP may be associated with clinical severity in the early phase. Similarly, the moderate positive correlation observed between day 1 CSF IMA levels and day 1 HHS scores (r=0.471, p=0.036) indicates that early oxidative stress/ischemic responses may be associated with clinical severity.

On the other hand, a moderate negative correlation was observed between day 5 serum IMA and day 5 serum MBP levels (r=−0.492, p=0.028), which may appear contradictory. However, this finding may indicate that these biomarkers do not necessarily represent the same pathophysiological axis in all patients. In some cases, markers of myelin/axonal injury may predominate, whereas in others, oxidative stress responses may be more prominent. Considering the heterogeneous clinical course of SAH, this finding supports the possibility that different biological processes may contribute to disease progression with varying relative impact across individuals.

When studies evaluating the relationship between GOS and biomarkers are considered, heterogeneous associations between myelin basic protein (MBP) and functional outcome have been reported. Previous studies by Zheng et al. and Wasik et al. identified associations between elevated serum MBP levels and unfavorable long-term outcomes assessed at 3 and 6 months.9,26 In our study, no significant correlations were observed between GOS and serum MBP or serum IMA at any time point (all p>0.05). Functional outcome in our study was evaluated at the time of discharge or death, which may partly account for the lack of comparable MBP-GOS associations. Notably, unlike prior studies focusing primarily on serum biomarkers, the present analysis included cerebrospinal fluid measurements and identified a significant association between day 10 CSF IMA levels and GOS scores (r=−0.531, p=0.016). This finding underscores the potential relevance of CSF-based biomarkers in outcome assessment and highlights CSF IMA as a marker warranting further investigation in larger cohorts.

The presence of strong correlations among clinical grading scales supports the internal consistency of the cohort, including strong negative correlations between M. Fisher and GCS scores (day 1: r=−0.701, p=0.001; day 5: r=−0.736, p<0.001; day 10: r=−0.743, p<0.001) and strong positive correlations between M. Fisher and Hunt–Hess/WFNS scores across all time points (all p<0.001).

The significant early increase of MBP levels in both serum and CSF suggests that MBP may represent a promising biomarker candidate for monitoring secondary brain injury following SAH. Although no significant temporal change was observed in serum IMA levels, the finding that CSF IMA demonstrated significant correlations with clinical deterioration, particularly on day 10, suggests that CSF IMA may have prognostic relevance during the later phase of the disease course. Notably, the significant association observed between day 10 CSF IMA levels and GOS scores further supports the potential value of CSF IMA in relation to early functional outcome assessment. Future studies with larger sample sizes, stratification according to the presence of vasospasm, and support from multivariate analyses will be necessary to clarify the clinical utility and potential translational applicability of these biomarkers.

The main limitations of this study are the relatively small sample size (n=20) and the absence of long-term follow-up data. Although the limited cohort size may restrict statistical power and generalizability, the consistency of biomarker trends and their correlations with established clinical grading scales support the internal validity of the findings. In addition, functional outcome was assessed at discharge, precluding evaluation of long-term prognostic implications; therefore, larger prospective studies with extended follow-up are warranted to further clarify the clinical relevance of these biomarkers.

Adil Ugur Yavuz: 0000-0002-5623-3116

This study was approved by the Karadeniz Technical University Faculty of Medicine Scientific Research Ethics Committee (Institutional Review Board approval number 2022/174, dated 29/07/2022), and all procedures involving human participants were conducted in accordance with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.

Written informed consent was obtained from all individual participants included in the study. The confidentiality of all participants was protected.

None declared.

No funding was received for this study.

The authors declare no conflicts of interest.