Derivation and validation of a novel and parsimonious prognosis prediction score for ischemic stroke patients: The S2AFI Score

Background: To develop and validate a novel and integer-based score to predict the unfavorable outcome at 3-month after ischemic stroke using a dataset from the Chinese population. Methods We retrospectively included 394 patients presented to our stroke center within 24 hours after symptom onset. 70% of them were randomly selected as the model derivation dataset and the remaining 30% as the model validation dataset. Step-wise logistic regression were applied to identify the strong predictors of the unfavorable outcome, which was defined as modified Rankin Scale (mRS) >2. Results We identified 4 strong predictors in the final prediction model: stroke severity, age, serum fibrinogen level and intravenous thrombolytic therapy. 2 points were assigned when patients with NIH stroke scale higher than 6 at admission. 1 point was assigned to patients older than 71 years old and serum fibrinogen level higher than 2.98g/L respectively. For patients miss the opportunity of intravenous thrombolysis therapy, 1 point was assigned. We called our score system as S2AFI score and it ranges from 0 to 5. The Youden index of the S2AFI score was 2 which means patients with 3 points or higher tend to have unfavorable outcome in the future. The discriminative ability of the S2AFI score as dichotomized predictor achieved an area under the curve of 0.72 (95% Confidence Internal 0.66-0.79) in the derivation dataset, 0.72 (95% Confidence Internal 0.61-0.83) in the validation dataset and 0.68 (95% Confidence Internal 0.63-0.74) in all patients. While for the S2AFI score as continuous predictor, the score achieved an area under the curve of 0.76 (95% Confidence Internal 0.69-0.83) in the derivation dataset, 0.74 (95% Confidence Internal 0.62-0.87) in the validation dataset and 0.74 (95% Confidence Internal 0.68-0.80) in all patients. There was a strong correlation between the S2AFI score and the risk of unfavorable outcome at 3-month (P for trend <0.001). Conclusions Our novel and parsimonious S2AFI score had good performance in the prediction of unfavorable outcome at 3-month after ischemic stroke.