Table 2 Outcome measurement tools and results of the selected studies (*Data presented as median [quartiles]; **Data presented as mean ± SD).

Brea et al.¹⁵

Good (≤ 2) or bad (> 2) outcome, assessed by the mRS 90 days after the stroke onset

NSE levels at ED admission did not present statistical significance with the outcome (p = 0.067; good: 8.5 [5.2, 11.9]; bad: 9.2 [5.3, 12.1] ng/ml)*

Ghosh et al.¹¹

Mild (0–4), moderate (5–15), or severe (16–42) stroke, assessed by the NIHSS at ED admission; mRS score < 2 or mRS score ≥ 2 30 days post-discharge

NSE levels at ED admission were positively correlated with the stroke severity (mild: 24.5 ± 5.4; moderate: 37 ± 11.9; severe: 56 ± 20.5 ng/ml) with statistical significance between mild and severe groups (p < 0.0001) and the functional outcome (mRS < 2: 30.6 ± 6.8; mRS ≥ 2: 47 ± 16.87 ng/ml) also with statistical significance (p = 0.0021)**

Jauch et al.¹⁶

NIHSS at ED admission; CT scans 24 h and three months after admission; mRS three months after admission

NSE levels were not associated with stroke severity, infarcted brain volume, or functional outcome, even after adjusting for treatment arm, history of hypertension, NIHSS at baseline, early ischemic changes on initial CT, and admission systolic blood pressure (p > 0.247)

Kurakina et al.⁹

NIHSS and GCS at ED admission; CT scan at ED admission; Good (≤ 2) or bad (> 2) outcome, assessed by the mRS 12–14 days after stroke onset; Death or not 14 days after the stroke onset

NSE levels at ED admission were positively correlated with the severity of neurological symptoms (r = 0.33; p = 0.02), the infarcted brain volume (r = 0.49; p = 0.003), the functional outcome (p = 0.04; good: 1.7 [1.4, 1.8]; bad: 2.1 [1.7, 3.0] ng/ml) and the death rates (p = 0.02; died: 3.0 [1.7, 6.0]; survived: 1.9 [1.5, 2.6] ng/ml) with statistical significance, but not with the GCS at ED admission (r = − 0.22; p = 0.15). The threshold of 2.6 ng/ml in NSE levels was established on the Receiver Operating Characteristic (ROC) curve to distinguish between patients who died and those who survived with a sensitivity of 74.7% and specificity of 71.4% (Area Under the Curve of 0.77; 95% Confidence Interval: 0.60–0.95; p = 0.02). NSE levels above 2.6 ng/ml during the acute ischemic stroke period were associated with an unfavorable prognosis regarding the likelihood of a lethal outcome (Odds Ratio = 8.3; p = 0.01)*

Oh et al.¹⁷

NIHSS at ED admission and MRI one week after the stroke onset

NSE levels at ED admission were positively correlated with the stroke severity (r = 0.42) and the infarcted brain volume (r = 0.62) with statistical significance (p < 0.002 and p < 0.001, respectively)

Oh et al.¹⁸

NIHSS at ED admission and mRS after three months of follow-up

NSE levels at ED admission were positively correlated with the stroke severity (r = 0.589) and the functional outcome (r = 0.635) with statistical significance (p < 0.05)

Park et al.¹⁹

Favorable (≤ 2) or poor (> 2) outcome, assessed by the mRS after three months of follow-up

NSE levels at ED admission did not correlate with the functional outcome (favorable: 5.6 [1.6, 10.3]; poor: 7.7 [3.0, 11.5]) with statistical significance (p = 0.14). Multivariate logistic regression analysis did not show statistical significance (p = 0.209), even after adjustment for age and initial NIHSS score (p = 0.325)*

Purroy et al.¹⁰

Diffusion-weighted imaging (DWI) within a week after the stroke onset

NSE levels at ED admission were significantly correlated with infarcted brain volume (p = 0.001; Spearman’s coefficient = 0.191). However, for a linear regression analysis adjusted by etiology, the correlation was lost

Shash et al.¹²

NIHSS at ED admission; Death or not 16 days after stroke onset

NSE levels at ED admission were significantly and positively correlated with clinical stroke severity among the patients (r = 0.737, p = 0.000), and this positive correlation was higher in the death group than in the no-death group (r = 0.853, p = 0.000 and r = 0.685, p = 0.03, respectively). The cutoff value of the NSE level to anticipate mortality at ED admission was > 33.45 ng/mL, with a sensitivity of 66.67% and specificity of 96.77%. The cutoff value of the NSE level to predict mortality at 48 h was > 31.04 ng/mL, with a sensitivity of 66.67% and specificity of 93.55%. The mean value of NSE level at ED admission was significantly higher in the death group (34.5 ± 6.2 ng/mL) than in the no-death group (23.1 ± 8.1 ng/mL) (p = 0.007)**

Singh et al.²⁰

NIHSS at ED admission

Compared to the initial NSE levels in the mild (5.74 ± 1.16), moderate (12.05 ± 1.5), and severe groups (16.3 ± 0.58), NSE levels were found to be significantly higher in the severe group. NSE levels in stroke patients and the degree of neurological deficit were significantly correlated (r = 0.8, p ≤ 0.001)**

Wunderlich et al.²¹

CT scans within the first week after stroke onset

NSE levels at ED admission were significantly correlated with infarcted brain volume (r² = 0.15, p = 0.005)