Table 2.

Details of data collection and outcome assessment

Variables	Details of method
Baseline data
Stroke severity	Stroke severity was assessed using the National Institutes of Health Stroke Scale by trained neurologists at baseline
Ischemic stroke subtypes	Trial of ORG 10172 in Acute Stroke Treatment (TOAST) classification criterion was used to classify the ischemic stroke subtypes according to the symptoms and imaging data of the patients 1. Large-artery atherosclerosis (Thrombotic) 2. Cardiac embolism (Embolic) 3. Small-vessel occlusion (Lacunar)
Education	Educational attainment was assessed as 0–17 magnitude from the uneducated to higher education.
Blood pressure	Three blood pressure measurements were obtained at baseline while the patient was in the supine position using a standard mercury sphygmomanometer according to European Society of Cardiology guidelines.
Routine laboratory determinations	Routine laboratory determinations (fasting plasma glucose, blood lipids, etc.) were tested for all enrolled patients in each participating hospital at admission
Renal function	Assessment of renal function was based on estimated glomerular filtration rate calculated using the Chronic Kidney Disease Epidemiology Collaboration creatinine equation with adjusted coefficient of 1.1 for the Chinese population. According to the Kidney Disease: Improving Global Outcomes, we defined normal renal function as estimated glomerular filtration rate ≥ 90 mL/min per 1.73 m2 and abnormal renal function as estimated glomerular filtration rate < 90 mL/min per 1.73 m2.
Cystatin C test
Blood sample collection	Blood samples were collected after at last 8 h of fasting within 24 h of hospital admission. All serum samples were separated and frozen at −80°C in the Central Laboratory of School of Public Health in Soochow University, China until laboratory testing.
Cystatin C assay kit	Serum Cystatin C levels were determined with a Cystatin C assay kit by latex enhanced immunoturbidimetric method (Sichuan Maker Biotechnology Co., Ltd., China), and the Cystatin C calibrator was the primary reference material ERM-DA471/IFCC for cystatin C assays
Quality control	The range of Cystatin C measurement was from 0.13 to 7.80 mg/L. Intra- and inter-assay coefficients of variation were less than 3.9% and 4.8%, respectively.
Outcome assessment
Study outcome	The study outcome was cognitive impairment at 3 months after stroke onset assessed by trained neurologists using the Mini-Mental State Examination. The MMSE contains 20 items that test cognitive performance in domains including orientation, registration, attention and calculation, recall, language, and visual construction. MMSE has been translated into Chinese and validated as a screening tool for cognitive impairment and dementia in the Chinese population. In this analysis, a score of < 27 on the Mini-Mental State Examination indicated cognitive impairment