AIMS: We explored if the association is explained by shared risk factors or is independent and whether there are regional or stroke subtype variations.

METHODS: INTERSTROKE is a case-control study and the largest international study of risk factors for first acute stroke, completed in 27 countries. We included individuals with available serum creatinine values and calculated estimated glomerular filtration rate (eGFR). Renal impairment was defined as eGFR <60 mL/min/1.73 m2. Multivariable conditional logistic regression was used to determine the association of renal function with stroke.

RESULTS: Of 21,127 participants, 41.0% were female, the mean age was 62.3 ± 13.4 years, and the mean eGFR was 79.9 ± 23.5 mL/min/1.73 m2. The prevalence of renal impairment was higher in cases (22.9% vs. 17.7%, p < 0.001) and differed by region (p < 0.001). After adjustment, lower eGFR was associated with increased odds of stroke. Renal impairment was associated with increased odds of all stroke (OR 1.35; 95% CI: 1.24-1.47), with higher odds for intracerebral hemorrhage (OR 1.60; 95% CI: 1.35-1.89) than ischemic stroke (OR 1.29; 95% CI: 1.17-1.42) (pinteraction 0.12). The largest magnitudes of association were seen in younger participants and those living in Africa, South Asia, or South America (pinteraction < 0.001 for all stroke). Renal impairment was also associated with poorer clinical outcome (RRR 2.97; 95% CI: 2.50-3.54 for death within 1 month).

METHODS: We studied the patterns and effect of practice variations (ie, treatments used and access to services) among participants in the INTERSTROKE study, an international observational study that enrolled 13 447 stroke patients from 142 clinical sites in 32 countries between Jan 11, 2007, and Aug 8, 2015. We supplemented patient data with a questionnaire about health-care and stroke service facilities at all participating hospitals. Using univariate and multivariate regression analyses to account for patient casemix and service clustering, we estimated the association between services available, treatments given, and patient outcomes (death or dependency) at 1 month.

FINDINGS: We obtained full information for 12 342 (92%) of 13 447 INTERSTROKE patients, from 108 hospitals in 28 countries; 2576 from 38 hospitals in ten high-income countries and 9766 from 70 hospitals in 18 low and middle-income countries. Patients in low-income and middle-income countries more often had severe strokes, intracerebral haemorrhage, poorer access to services, and used fewer investigations and treatments (p<0·0001) than those in high-income countries, although only differences in patient characteristics explained the poorer clinical outcomes in low and middle-income countries. However across all countries, irrespective of economic level, access to a stroke unit was associated with improved use of investigations and treatments, access to other rehabilitation services, and improved survival without severe dependency (odds ratio [OR] 1·29; 95% CI 1·14-1·44; all p<0·0001), which was independent of patient casemix characteristics and other measures of care. Use of acute antiplatelet treatment was associated with improved survival (1·39; 1·12-1·72) irrespective of other patient and service characteristics.

INTERPRETATION: Evidence-based treatments, diagnostics, and stroke units were less commonly available or used in low and middle-income countries. Access to stroke units and appropriate use of antiplatelet treatment were associated with improved recovery. Improved care and facilities in low-income and middle-income countries are essential to improve outcomes.

METHODS: We obtained random urine samples from 9,275 cases of acute first stroke and 9,726 matched controls from 27 countries and estimated the 24-hour sodium and potassium excretion, a surrogate for intake, using the Tanaka formula. Using multivariable conditional logistic regression, we determined the associations of estimated 24-hour urinary sodium and potassium excretion with stroke and its subtypes.

RESULTS: Compared with an estimated urinary sodium excretion of 2.8-3.5 g/day (reference), higher (>4.26 g/day) (odds ratio [OR] 1.81; 95% confidence interval [CI], 1.65-2.00) and lower (<2.8 g/day) sodium excretion (OR 1.39; 95% CI, 1.26-1.53) were significantly associated with increased risk of stroke. The stroke risk associated with the highest quartile of sodium intake (sodium excretion >4.26 g/day) was significantly greater (P < 0.001) for intracerebral hemorrhage (ICH) (OR 2.38; 95% CI, 1.93-2.92) than for ischemic stroke (OR 1.67; 95% CI, 1.50-1.87). Urinary potassium was inversely and linearly associated with risk of stroke, and stronger for ischemic stroke than ICH (P = 0.026). In an analysis of combined sodium and potassium excretion, the combination of high potassium intake (>1.58 g/day) and moderate sodium intake (2.8-3.5 g/day) was associated with the lowest risk of stroke.

METHODS: We undertook a standardised case-control study in 32 countries (INTERSTROKE). Cases were patients with acute first stroke (n=13 462) who were matched by age, sex and site to controls (n=13 483). We evaluated the associations of knowledge, awareness and treatment of hypertension with risk of stroke and its subtypes and whether this varied by gross national income (GNI) of country. We estimated OR and population attributable risk (PAR) associated with treated and untreated hypertension.

RESULTS: Hypertension was associated with a graded increase in OR by reducing GNI, ranging from OR 1.92 (99% CI 1.48 to 2.49) to OR 3.27 (2.72 to 3.93) for highest to lowest country-level GNI (p-heterogeneity<0.0001). Untreated hypertension was associated with a higher OR for stroke (OR 5.25; 4.53 to 6.10) than treated hypertension (OR 2.60; 2.32 to 2.91) and younger age of first stroke (61.4 vs 65.4 years; p<0.01). Untreated hypertension was associated with a greater risk of intracerebral haemorrhage (OR 6.95; 5.61 to 8.60) than ischaemic stroke (OR 4.76; 3.99 to 5.68). The PAR associated with untreated hypertension was higher in lower-income regions, PAR 36.3%, 26.3%, 19.8% to 10.4% by increasing GNI of countries. Lifetime non-measurement of blood pressure was associated with stroke (OR 1.80; 1.32 to 2.46).

METHODS: The INTERSTROKE study is a case-control study of acute first stroke and was undertaken with 13,462 stroke cases and 13,488 controls recruited between January 11, 2007 and August 8, 2015 in 32 countries worldwide. Association of risk of tobacco use and ETS exposure were analysed with overall stroke, ischemic and intracerebral hemorrhage (ICH), and with TOAST etiological stroke subtypes (large vessel, small vessel, cardioembolism, and undetermined).

FINDINGS: Current smoking was associated with an increased risk of all stroke (odds ratio [OR] 1.64, 95% CI 1.46-1.84), and had a stronger association with ischemic stroke (OR 1.85, 95% CI 1.61-2.11) than ICH (OR 1.19 95% CI 1.00-1.41). The OR and PAR of stroke among current smokers varied significantly between regions and income levels with high income countries (HIC) having the highest odds (OR 3.02 95% CI 2.24-4.10) and PAR (18.6%, 15.1-22.8%). Among etiological subtypes of ischemic stroke, the strongest association of current smoking was seen for large vessel stroke (OR 2.16, 95% CI 1.63-2.87) and undetermined cause (OR 1.97, 95% CI 1.55-2.50). Both filtered (OR 1.73, 95% CI 1.50-1.99) and non-filtered (OR 2.59, 95% CI 1.79-3.77) cigarettes were associated with stroke risk. ETS exposure increased the risk of stroke in a dose-dependent manner, exposure for more than 10 h per week increased risk for all stroke (OR 1.95, 95% CI 1.69-2.27), ischemic stroke (OR 1.89, 95% CI 1.59-2.24) and ICH (OR 2.00, 95% CI 1.60-2.50).

INTERPRETATION: There are significant variations in the magnitude of risk and PAR of stroke according to the types of tobacco used, active and ETS exposure, and countries with different income levels. Specific strategies to discourage tobacco use by any form and to build a smoke free environment should be implemented to ease the global burden of stroke.