Table 1.

Synopsis of the studies.

References	Inclusion criteria	Exclusion criteria	Primary endpoint
Jamali et al. (72)	Patients (≥18 years) with a diagnosis of SAH	Preexisting immunocompromised state, autoimmune disorders, hematologic disorders, and malignancies	Overall inpatient mortality; incidence of pneumonia during hospitalization
Wang et al. (73)	Patients with a diagnosis of SAH and rebleeding confirmed by CT. CTA or DSA was used to verify the presence of the intracranial aneurysm	The patients presented with other cerebrovascular diseases and intracranial tumors; multiple intracranial aneurysms; a malignant tumor; leukemia; hemolytic anemia; antiplatelet or anticoagulant-associated ICH; with pneumonia within 72 h following SAH	Rebleeding within 72 h following aSAH; 3 months outcome (favorable: mRS score 0–2; poor: mRS score 3–5)
Al-Mufti et al. (74)	Patients (≥18 years) with a diagnosis of SAH verified by admission CTA and DSA	SAH secondary to perimesencephalic bleeds, related to trauma, rupture of an arteriovenous malformation, or other causes	DCI (focal neurological impairment or a decrease in at least two points on GCS); poor outcome (death or moderate to severe disability: unable to walk or tend to bodily needs, mRS score of 4–6)
Giede-Jeppe et al. (75)	Patients with a diagnosis of SAH verified by admission CTA and DSA	Missing outcome data and missing NLR levels, patients suffering from infections	3 months outcome (favorable: mRS score 0–2; unfavorable: mRS score 3–6) and mortality; 12 months outcome and mortality; in-hospital complications
Ray et al. (76)	Patients with a diagnosis of SAH verified by admission CTA and DSA	Patients without appropriate CT scans, lost to follow-up or revoked consent; in-hospital death	1 year outcome (mRS score of 3–6, MoCA <26), DCI (a new hypodensity on CT and/or associated symptoms)
Wu et al. (77)	Patients with a diagnosis of SAH, verified by CT, received standard medical treatment	Patients with traumatic SAH, recent infectious diseases, and prior neurological conditions, including ischemic stroke, hemorrhagic stroke, or brain trauma	DCI (focal impairment or a decrease of at least 2 points on the GCS, without other causes)
Ogden et al. (78)	Patients (≥16 years) admitted to the emergency room and diagnosed with SAH on CT and then treated in the ICU	Patients whose data were incomplete, with head and general body trauma and with spontaneous intracerebral hematoma which drained into the ventricle	N/A
Yilmaz et al. (79)	Patients diagnosed as SAH by CT, MRI, and CTA	Patients with endocrinologic disorders, hematologic and rheumatologic diseases, malignancy, history of autoimmune diseases, immunosuppressive drug intake, acute or chronic infection, use of antiaggregant, anticoagulants, or analgesics	In-hospital mortality
Huang et al. (80)	Patients (≥15 years) with a diagnosis of SAH verified by ICD9*	Patients who have been previously admitted to ICU were excluded	Hospital death; 1 year mortality
Tao et al. (81)	Patients (≥18 years) with a first aSAH confirmed by DSA; received aneurysm repair treatment within 72 h after admission; initial blood sampling for laboratory test including NLR/PLR was limited within 24 h after ictus of hemorrhage	Patients with acute or chronic infection, history of autoimmune disease, previous stroke and recent cardiocerebrovascular disease, previous use of anticoagulant/antiplatelet medication, suffered aneurysm rebleeding before surgery and declined surgical intervention, other prior systemic diseases	DCI (a decrease of at least 2 points on the GCS) and 3 months outcome (poor: mRS score of ≥3)
Zhang et al. (82)	Patients (≥18 years) had an acute headache attack and underwent CT	Patients with acute or chronic inflammatory diseases, hematological diseases, cancers, autoimmune diseases, hepatic or renal insufficiency, cerebral hemorrhage, acute ischemic stroke or other trauma diseases, and patients whose clinical data were incomplete	Neutrophil, NLR, and PLR in SAH and non-traumatic acute headache

^*ICD9: code = 430 and sequence = 1 on MIMIC II database.

SAH, subarachnoid hemorrhage; aSAH, aneurysmal SAH; CT, computed tomography; CTA, CT angiography; DSA, digital subtraction angiography; ICH, intracerebral hemorrhage; mRS, Modified Rankin Scale; DCI, delayed cerebral ischemia; GCS, Glasgow Coma Scale; NLR, neutrophil-to-lymphocyte ratio; MoCA, Montreal cognitive assessment; ICU, intensive care unit; PLR, platelet-to-lymphocyte ratio.