Proteinuria and risk of stroke in patients with hypertension: The Kailuan cohort study

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1 Received: 30 October 2017 Revised: 8 February 2018 Accepted: 13 February 2018 DOI: /jch ORIGINAL PAPER Proteinuria and risk of stroke in patients with hypertension: The Kailuan cohort study Anxin Wang PhD 1,2,3,4,5,6 Liye Dai MD 1 Zhaoping Su MD 1,2,3,4 Shuohua Chen MD 7 Junjuan Li MD 8 Shouling Wu MD 7 Yongjun Wang MD 1,2,3,4 Yilong Wang MD, PhD 1,2,3,4 1 Department of Neurology, Beijing Tiantan Hospital, Capital Medical University, Beijing, China 2 China National Clinical Research Center for Neurological Diseases, Beijing, China 3 Center of Stroke, Beijing Institute for Brain Disorders, Beijing, China 4 Beijing Key Laboratory of Translational Medicine for Cerebrovascular Disease, Beijing, China 5 Beijing Municipal Key Laboratory of Clinical Epidemiology, Beijing, China 6 Department of Epidemiology and Health Statistics, School of Public Health, Capital Medical University, Beijing, China 7 Department of Cardiology, Kailuan Hospital, North China University of Science and Technology, Tangshan, China 8 Department of Nephrology, Kailuan Hospital, North China University of Science and Technology, Tangshan, China Correspondence Yilong Wang, MD, PhD, Department of Neurology, Beijing Tiantan Hospital, Capital Medical University, Beijing, China. yilong528@gmail.com Proteinuria is associated with stroke, but the effects of changes in proteinuria on stroke risk are not well understood in the hypertensive population. This study examined whether proteinuria changes across 2- year assessments were associated with incident stroke in individuals with hypertension. We used visit data from participants with hypertension of the Kailuan study who were stroke free at baseline. Based on the baseline and 2- year dipstick screening results, participants were classified as having no, remittent, incident, or persistent proteinuria. The relationship between proteinuria and stroke was analyzed using Cox proportional- hazards models after adjusting for potential variables. During a median of year follow- up, we identified 1197 people with stroke. Compared to those with no proteinuria, stroke risk was significantly increased in participants with incident (hazard ratio [HR] 1.41, 95% CI, ) and persistent proteinuria (HR 1.49, 95% CI, ) after adjustment for other factors, which was consistent in ischemic stroke and intracerebral hemorrhage. No interaction was found between changes of proteinuria and diabetes mellitus in the hypertensive population. Changes in proteinuria exposure, particularly persistent proteinuria, play a role in reflecting the risk of stroke in patients with hypertension. 1 INTRODUCTION Studies demonstrated that a decreased level of kidney function is an independent risk factor for all- cause mortality as well as adverse cardiovascular disease outcomes including myocardial infarction, stroke, and progression of heart failure. 1-4 As an important marker of chronic kidney disease (CKD), proteinuria was proved to be associated with incident stroke during the last few decades. 5 Data suggested that baseline proteinuria confers a 50%- 92% greater risk of future stroke. 6 Previous study demonstrated that the prevalence of proteinuria was higher in the hypertensive group than in the normotensive group (hypertensive group, 33.9%; normotensive, 10%). 7 Furthermore, data from the China National Stroke Screening Survey (CNSSS) showed that hypertension ranked in first place among factors contributing to stroke in China. 8 The association between proteinuria and stroke, in particular, should be noted in the hypertensive population who are at high risk for the development of stroke. More important, proteinuria often changes dynamically, showing regression or progression. 9 However, an inherent limitation of previous studies is the reliance on a single time point by which to assess kidney damage and events using baseline proteinuria. The value of multiple dipstick measurements for changes in proteinuria and its relation with stroke outcomes has rarely been investigated. Anxin Wang and Liye Dai contributed equally to the manuscript. J Clin Hypertens. 2018;20: wileyonlinelibrary.com/journal/jch 2018 Wiley Periodicals, Inc. 765

2 766 WANG et al. Therefore, we conducted this study to assess the relationship between proteinuria change and stroke incidence in participants with hypertension. 2 METHODS 2.1 Study population The design, method, rationale, and examination details of the Kailuan cohort study have been published previously In brief, the Kailuan study is a population- based prospective cohort study. Between June 2006 and October 2007, a total of individuals aged were recruited to participate in the study and were followed up until present by means of biennial face- to- face examinations and annual comprehensive surveillance of medical records and death certificates. All participants recruited underwent routine history and physical examination, anthropometry, and laboratory assessment. Out of the whole cohort at the first examination, hypertensive participants without previous stroke and with complete dipstick assessment of proteinuria participated in the second examination of the Kailuan study in the year Hypertension was defined as systolic blood pressure (SBP) at least 140 mm Hg or diastolic blood pressure (DBP) at least 90 mm Hg or history of hypertension and/or use of antihypertensive agents. After exclusion for new finding of stroke during the period to or missing proteinuria data, participants remained eligible for the present analysis. A flowchart of the present cohort study is shown in Figure 1. All participants provided informed consent. The study was performed according to the guidelines of the Helsinki Declaration and was approved by the Ethics Committee of the Kailuan Hospital and the Beijing Tiantan Hospital. 2.2 Measurements of proteinuria At the baseline examination, a dipstick urine analysis was performed. The urine dipstick is a widely used tool in clinical screening for proteinuria on the basis of easy accessibility and low cost. 14 Dipstick positive proteinuria, seen as a sign of chronic kidney disease (CKD), has emerged as a powerful and independent predictor of cardiovascular disease. 6 In this study, proteinuria was screened by dipstick strictly following the direction of the kit. A freshly obtained urine sample was first visually examined for 1 minute by a trained physician (H12-MA, DIRUI N-600). 15 Using a color scale, the results of the urine strip test were semiquantified as absent, trace, 1+, 2+, or 3+. Proteinuria positive was defined as trace or more with dipstick analysis either at baseline or at the follow- up visit. We defined 4 proteinuria groups according to changes in proteinuria from baseline to the follow- up visit. Based on the baseline and 2- year dipstick screening results, participants were classified as having no, remittent, incident, or persistent proteinuria. No proteinuria was defined as proteinuria absent both at the baseline visit and at the follow- up visit. Remittent proteinuria was defined as proteinuria present at the baseline but absent at the follow- up visit. Incident proteinuria was defined as proteinuria absent at the baseline visit but occurring at the follow- up visit. Persistent proteinuria was defined as proteinuria present at the baseline visit and also at the follow- up visit. Reduction in proteinuria was defined as baseline minus 2- year proteinuria. 2.3 Potential covariates The variables involved in this research including age, gender, current smoker, current alcohol, physical activity, body mass index, diabetes mellitus, dyslipidemia, total cholesterol, triglycerides, low- density lipoprotein, high- density lipoprotein, systolic blood pressure, diastolic blood pressure, fasting blood glucose, and estimated glomerular filtration rate (egfr). All these variables were mentioned and described in previous studies. Data on smoking, drinking, physical activity, and other demographic variables including sex and age were collected using questionnaires. SBP and DBP were measured twice in the seated position using a mercury sphygmomanometer. The average of the 2 readings was used for the analyses. The change of blood pressure was calculated by diastolic in 2008-diastolic in We included this FIGURE 1 Flowchart of the study

3 WANG et al. 767 variable to decrease the influence of progression by blood pressure. Weight and height were measured during the interview and body mass index (BMI) was calculated as weight (kg)/height (m) ². Blood pressure was measured with a standard mercury sphygmomanometer by a physician or trained nurses. Blood samples were collected from the antecubital vein after an overnight fast. All blood samples were tested using a Hitachi 747 auto- analyzer (Hitachi, Tokyo, Japan) at the central laboratory of the Kailuan General Hospital for serum total cholesterol, low- density lipoprotein cholesterol (LDL- C), high- density lipoprotein cholesterol (HDL- C), fasting blood glucose (FBG), and other factors. Previous history of disease, including hypertension, diabetes mellitus, and hyperlipidemia, was collected by self- report. The use of medicine such as antihypertensives within the past 2 weeks before the baseline interview was also self- reported. 2.4 Follow- up and stroke assessment We considered the 2008 survey as the starting point and December 31, 2015 as the endpoint of the follow- up in the present prospective study. Follow- up evaluations included biennial measurements of laboratory parameters and the occurrence of adverse events. The outcome was the first occurrence of stroke, either the first nonfatal stroke event or stroke death without a preceding nonfatal event. A nonfatal stroke is defined as the sudden onset of a focal neurological deficit with a vascular mechanism lasting > 24 hours, including hemorrhagic stroke, ischemic stroke, and subarachnoid hemorrhage. Stroke is diagnosed according to the World Health Organization criteria combined with a brain computed tomography (CT) or magnetic resonance (MR) for confirmation 16 and classified into 3 types: cerebral infarction, cerebral hemorrhage, and subarachnoid hemorrhage. Subarachnoid hemorrhage was usually based on aneurysm or vascular malformation instead of chronic stroke risk factors. Considering the small sample size (n = 31) and different mechanism, we did not include the subarachnoid hemorrhage group in the subgroup analysis. The diagnostic criteria were consistent across all participating hospitals and all stroke outcomes were validated by the Data Safety Monitoring Board and the Arbitration Committee for Clinical Outcomes. The outcome information was further confirmed by checking discharge summaries and the medical records from medical insurance. For analysis of stroke- specific data, patients who ended up with unrelated causes were considered as censored. 2.5 Statistical analyses Continuous variables were described as means ± standard deviation (SD) and were compared using ANOVA or Kruskal- Wallis test. Categorical variables were described as counts (percentages) and were compared using the chi- square test or the Fisher exact test. Incidence rates of stroke were calculated per 1000 person- years of follow- up. Participants contributed person- time of follow- up from the date of return of the 2- year survey questionnaire to either the date of stroke onset, death, or end of followup. Cox proportional- hazards regression was used to calculate the hazard ratio and 95% confidence interval (CI) for stroke outcomes by changes in proteinuria, using participants with no proteinuria as the reference group. Variables with a P value <.2 and the well- established predictors were selected as adjustment covariates into the multivariable analyses. We fitted 3 multivariable Cox proportional hazards models. Model 1 was adjusted for age and sex. Model 2 was further adjusted for current smoker, current alcohol user, physical activity, and body mass index. Model 3 was adjusted for variables in model 2 plus diabetes mellitus, dyslipidemia, total cholesterol, high- density lipoprotein, systolic blood pressure, change of blood pressure, fasting blood glucose, and egfr. We used these models with a sandwich covariance matrix as a random effect to account for the potential confounding effect of the 11 different hospitals in the study. In the analysis of stroke risk for per- degree decrease of proteinuria, baseline proteinuria was adjusted in addition to the three models. To test the robustness of our findings, we conducted model 3 in participants excluding individuals with egfr < 30 ml/min/1.73 m² in 2008 as sensitive analysis. Furthermore, we tested interactions between changes in proteinuria with diabetes mellitus and sex for the risk of stroke. 3 RESULTS A total of participants with available data of proteinuria (men, 82.35%) were analyzed in our study. The mean age of the remaining population was ± years. We divided the participants into 4 categories according to changes in proteinuria from 2006 to The baseline characteristics in both 2006 and 2008 of the 4 categories of participants are shown in Table 1. For changes in proteinuria, 77.4% had no proteinuria, whereas 7.14% had remittent proteinuria, 10.60% had incident proteinuria, and 4.81% had persistent proteinuria. Differences in age, sex, BMI, physical activity, cholesterol concentration, egfr, blood pressure, concomitant morbidities (diabetes or dyslipidemia), and medicine treatment were found between proteinuria change groups (P <.05) in both 2006 and No significant differences in participants who smoke or taking antilipidemic agents were observed between groups. Characteristics of participants included and excluded are showed in Table S1. During a median follow- up of 6.89 (6.56, 7.19) years, we identified 1197 subjects with incident strokes. The incident stroke rate was 6.32 events per 1000 person- years for subjects with no proteinuria, 8.76 for remittent proteinuria, for incident proteinuria, and for persistent proteinuria. We additionally analyzed the association between stroke and different proteinuria level. The result is shown in Table 2. The relationship between stroke and proteinuria is not consistent from 2006 to Table 3 shows the adjusted HRs of incident stroke and subtypes associated with changes in proteinuria exposure. Compared with subjects without proteinuria, HRs for stroke were 1.63 (95% CI, ) for incident proteinuria, and 2.04 (95% CI, ) for persistent proteinuria (Model 1), attenuated but still significant after fully adjustment. The same trends were found in the association between changes in proteinuria

4 768 WANG et al. TABLE 1 Characteristics in 2006 and 2008 according to the change in proteinuria from 2006 to 2008 in participants with hypertension Change of proteinuria Variable Total No proteinuria Remittent proteinuria Incident proteinuria Persistent proteinuria P value No. of participants Age, years ± ± ± ± ± <.0001 Sex, male, (82.35) (81.90) 491 (82.80) 2084 (85.76) 510 (83.33) <.0001 Baseline information in 2006 Current smoker, Current alcohol, Active physical activity, Antihypertension agents, Antidiabetes mellitus agents, Antilipidemic agents, Diabetes mellitus, Dyslipidemia, 8686 (35.74) 7503 (36.31) 226 (38.11) 784 (32.26) 173 (28.27) < (39.51) 8370 (40.50) 228 (38.45) 818 (33.66) 186 (30.39) < (20.67) 4401 (21.30) 166 (27.99) 373 (15.35) 84 (13.73) < (26.17) 5431 (26.28) 193 (32.55) 564 (23.21) 172 (28.10) < (3.67) 683 (3.31) 38 (6.41) 118 (4.86) 52 (8.50) < (1.51) 296 (1.43) 10 (1.69) 44 (1.81) 16 (2.61) (12.97) 2365 (11.44) 152 (25.63) 433 (17.82) 201 (32.84) < (42.98) 8710 (42.15) 313 (52.78) 1096 (45.10) 325 (53.10) <.0001 Body mass index, ± ± ± ± ± 4.02 <.0001 kg/m 2 Systolic blood pressure, mm Hg Diastolic blood pressure, mm Hg Fasting blood glucose, Total cholesterol, Triglycerides,, Low- density lipoprotein, High- density lipoprotein, Estimated glomerular filtration rate, ml/min/1.73 m² ± ± ± ± ± < ± ± ± ± ± < ± ± ± ± ± 2.98 < ± ± ± ± ± ± ± ± ± ± 1.92 < ± ± ± ± ± 1.23 < ± ± ± ± ± 0.42 < (25.42) (23.16) (22.44) (40.45) (22.16) < follow- up Current smoker, Current alcohol, 8726 (35.91) 7410 (35.86) 209 (35.24) 890 (36.63) 217 (35.46) (37.49) 7827 (37.88) 209 (35.24) 872 (35.88) 201 (32.84).0123 (Continues)

5 WANG et al. 769 TABLE 1 (Continued) Change of proteinuria Variable Total No proteinuria Remittent proteinuria Incident proteinuria Persistent proteinuria P value Active physical activity, Antihypertension agents, Antidiabetes mellitus agents, Antilipidemic agents, Diabetes mellitus, Dyslipidemia, 5513 (22.69) 4869 (23.56) 135 (22.77) 396 (16.30) 113 (18.46) < (19.98) 3988 (19.30) 159 (26.81) 523 (21.52) 185 (30.23) < (4.91) 880 (4.26) 61 (10.29) 169 (6.95) 82 (13.40) < (1.51) 296 (1.43) 10 (1.69) 44 (1.81) 16 (2.61) (7.46) 1351 (6.54) 83 (14.00) 257 (10.58) 121 (19.77) < (10.26) 2117 (10.24) 70 (11.80) 221 (9.09) 85 (13.89).0031 Body mass index, ± ± ± ± ± 3.91 <.0001 kg/m 2 Systolic blood pressure, mm Hg Diastolic blood pressure, mm Hg Fasting blood glucose, Total cholesterol, Triglycerides,, Low- density lipoprotein, High- density lipoprotein, Estimated glomerular filtration rate, ml/min/1.73 m² All-type stroke, ± ± ± ± (21.44) < ± ± ± ± ± < ± ± ± ± ± 2.96 < ± ± ± ± ± 1.29 < ± ± ± ± ± 2.84 < ± ± ± ± ± 0.96 < ± ± ± ± ± ± ± ± ± ± < (4.93) 920 (4.45) 42 (7.08) 183 (7.53) 52 (8.50) <.0001 Ischemic stroke 1003 (4.13) 779 (3.77) 36 (6.07) 143 (5.88) 45 (7.35) <.0001 Intracerebral hemorrhage Subarachnoid hemorrhage 203 (0.84) 151 (0.73) 6 (1.01) 38 (1.56) 8 (1.31) (0.13) 23 (0.11) 0 (0.00) 7 (0.29) 1 (0.16).1040 and stroke subtypes (ischemic stroke and hemorrhagic stroke). Notably, each degree of proteinuria decline was associated with a significant 12% reduction of stroke risk (HR 0.88, 95% CI, ), independent from age, sex, and other potential risk factors. Findings were consistent for stroke subtypes, with a 11% decrease (HR 0.89, 95% CI, ) for ischemic stroke and a 19% decrease (HR 0.81, 95% CI, ) for intracerebral hemorrhage. Sensitivity analysis yielded the same pattern of results in this entire test. Figure 2 shows the Kaplan- Meier cumulative risk for stroke and subtypes within groups defined by changes in proteinuria. Participants in the persistent proteinuria group experienced a higher risk than participants in the other groups during the year follow- up period for total stroke events (log- rank test, P <.01) (Figure 2A), ischemic stroke

6 770 WANG et al. TABLE 2 Stroke incidence rate and hazard ratios for stroke risk by proteinuria in participants with hypertension in 2006 and 2008 Proteinuria Stroke Ischemic stroke Intracerebral hemorrhage follow- up Ref Ref Ref Trace a 1.26 ( ) 1.25 ( ) 1.57 ( ) ( ) 1.08 ( ) 0.63 ( ) ( ) 1.36 ( ) 0.96 ( ) ( ) 2.19 ( ) 4.01 ( ) follow- up Ref Ref Ref Trace a 1.57 ( ) 1.72 ( ) 1.29 ( ) ( ) 1.37 ( ) 1.71 ( ) ( ) 1.13 ( ) 1.58 ( ) ( ) 1.49 ( ) 1.77 ( ) a Adjusted for age, gender, current smoker, current alcohol user, physical activity, body mass index, diabetes mellitus, dyslipidemia, total cholesterol, high- density lipoprotein, systolic blood pressure, fasting blood glucose, and egfr. TABLE 3 Stroke incidence rate and hazard ratios for stroke risk by changes in proteinuria in participants with hypertension Changes in proteinuria No proteinuria Remittent proteinuria Incident proteinuria Persistent proteinuria Per degree decrease a All- type stroke Incidence rate, per 1000 person- years Model 1 Reference 1.37 ( ) 1.63 ( ) 2.04 ( ) 0.82 ( ) Model 2 Reference 1.36 ( ) 1.60 ( ) 1.99 ( ) 0.85 ( ) Model 3 Reference 1.20 ( ) 1.41 ( ) 1.49 ( ) 0.88 ( ) Sensitive analysis b Reference 1.21 ( ) 1.40 ( ) 1.51 ( ) 0.92 ( ) Ischemic stroke Incidence rate, per 1000 person- years Model 1 Reference 1.40 ( ) 1.60 ( ) 2.02 ( ) 0.86 ( ) Model 2 Reference 1.39 ( ) 1.57 ( ) 1.97 ( ) 0.86 ( ) Model 3 Reference 1.19 ( ) 1.36 ( ) 1.41 ( ) 0.89 ( ) Sensitive analysis b Reference 1.20 ( ) 1.37 ( ) 1.42 ( ) 0.95 ( ) Intracerebral hemorrhage Incidence rate, per 1000 person- years Model 1 Reference 1.29 ( ) 1.65 ( ) 2.38 ( ) 0.80 ( ) Model 2 Reference 1.29 ( ) 1.65 ( ) 2.40 ( ) 0.79 ( ) Model 3 Reference 1.15 ( ) 1.99 ( ) 2.49 ( ) 0.81 ( ) Sensitive analysis b Reference 1.15 ( ) 2.04 ( ) 2.34 ( ) 0.87 ( ) Model 1: adjusted for age and gender. Model 2: adjusted for age, gender, current smoker, current alcohol user, physical activity, and body mass index. Model 3: adjusted for variables in model 2 plus diabetes mellitus, dyslipidemia, total cholesterol, high- density lipoprotein, systolic blood pressure, fasting blood glucose, and egfr. a Adjusted for proteinuria at baseline survey in addition to model 1, 2 and 3, respectively. b Adjusted for model 3 and further excluded individuals with an estimated glomerular filtration rate < 30 ml/min per 1.73 m 2 in 2008.

7 WANG et al. 771 FIGURE 2 Kaplan- Meier curve of (A) all- type stroke incidence rate; (B) ischemic stroke incidence rate; (C) intracerebral hemorrhage incidence rate by changes in proteinuria in participants with hypertension

8 772 WANG et al. (log-rank test, P <.01) (Figure 2B), and hemorrhagic stroke (log- rank test, P <.01) (Figure 2C). No interactions of proteinuria with diabetes mellitus (P =.14) or sex (P =.25) were found. 4 DISCUSSION In our study, the presence of proteinuria as detected by urine dipstick screening independently predicted an increased risk for incident stroke during median 6.89 years of follow- up. We observed significant associations of changes in proteinuria and the incidence of stroke and subtypes in the Chinese hypertensive population. This relationship persisted independently of other known major risk factors, including diabetes mellitus, dyslipidemia, and obesity. No interactions of proteinuria with sex contribute to this relationship. Compared with changes in proteinuria, proteinuria levels in different years are not consistent. This result indicated that compared with single measurement, changes in proteinuria might be a more stable risk factor for stroke. Proteinuria has acted as a risk multiplier of cardiovascular risk and mortality across all stages of kidney disease. 17 Assessing proteinuria using the simple urine dipstick test could be a convenient way to reflect an individual s systematic vasculature permeability and susceptibility to target organ damage. 18 Previous studies have reported that baseline proteinuria was associated with a higher stroke risk, with the risk greatest for ischemic stroke. 6,19 A recent study from the China Stroke Primary Prevention Trial also found that baseline proteinuria as measured by dipstick was an independent risk factor for first incident stroke and ischemic stroke. 20 A meta- analysis of cohort studies or randomized controlled trials also concluded that increasing albuminuria increased the risk of stroke. 21 Findings from the current study extend those from previous studies. Our study shows that the presence of proteinuria is associated with a substantially higher risk of incident stroke compared with an absence of proteinuria when measured either at baseline or at follow- up visits. As proteinuria often changes dynamically, showing regression or progression, 9 changes in proteinuria are more likely to reflect the risk of stroke, compared with proteinuria collected at a single time point in the hypertensive population. Previous study showed a 10% proteinuria reduction corresponded to 29% reduction of stroke in people with hypertension and/or diabetes. 22 Current result showed that each degree of proteinuria decline was associated with a significant 12% reduction of future stroke risk. This reinforces the concept that stroke risk is reduced when proteinuria is diminished, independent of other traditional cardiovascular risk factors. Our study investigated this association by distinguishing between ischemic and hemorrhagic stroke, as the patterns of results were consistent with total stroke. The effect size of changes in proteinuria for risks of stroke subtypes including ischemic stroke and hemorrhagic stroke was similar. In accordance with this result, previous studies also showed albuminuria was significant association with both stroke types. 23 Chronic kidney disease was highly prevalent among patients with type 2 diabetes mellitus. 24 According to previous studies, proteinuria was believed to be associated with diabetes mellitus. 41% increased risks for persistent proteinuria development over 20 years were found among 1304 participants with diabetes in the DCCT/EDIC study. 25 Elevated insulin levels are associated with increased vascular inflammation and, hence, the connection with proteinuria. 26 It is important to emphasize that this result showed there was no evidence of effect modification by diabetes mellitus. Changes in proteinuria are associated with stroke in the hypertensive population ignoring diabetes status. As corroboration, results from other studies also demonstrated that any degree of proteinuria is a risk factor for cardiovascular events in individuals with or without diabetes mellitus. 27 Screening for proteinuria to identify people at high risk of stroke is essential in the hypertensive population regardless of the diabetes status. The mechanism linking proteinuria to stroke risk remains obscure. The Steno hypothesis suggested that proteinuria not only reflects localized renal damage but also is an independent marker of systemic vascular endothelial dysfunction or microvascular disease. 28 Proteinuria is associated with several inflammatory and thrombogenic factors, which play important roles in the development of atherosclerosis and stroke. 21 Otherwise, proteinuria is associated with a high prevalence of traditional cardiovascular risk factors, such as hypertension and diabetes. Proteinuria may be a sign of shared risk factors for vascular disease and not a direct cause of new strokes. Urine protein change over time can be an indicator for the severity of those stroke risk factors. In the hypertensive population, proteinuria and hypertension have reciprocal effects. 7 Increased proteinuria in hypertensive patients is considered an early manifestation of generalized vascular impairment, which is regarded to be an important marker of the risk of renal and cardiovascular events. 29 According to these findings, we should pay more attention to proteinuria, especially in the hypertensive population. Hypertension and proteinuria are both clinical manifestation of renal disease, both also playing important roles in cardiovascular and cerebrovascular events. Whether proteinuria is a therapeutic target for stroke warrants clinical attention and further investigations. Strengths of our study were the ability to consider dynamic aspects of proteinuria using the biennial assessment of proteinuria to estimate the risk of stroke, the prospective design, use of a large cohort, and long follow- up period. Our results should be interpreted in the context of some limitations. First, awareness of the limitations of the dipstick test is necessary. The dipstick method could overlook proteinuria. 14 A timed 24 hours urine collection or albumin:creatinine ratio might be more precise in measuring proteinuria, although dipstick has a cost advantage. 30 Second, we have adjusted confounding variables when evaluating the proteinuria recorded in different years, but there were still some factors we failed to take into consideration. Last, unlike a randomized clinical trial, proteinuria could be associated with substantial morbidity and mortality in the population we excluded, which might be especially vulnerable

9 WANG et al. 773 to bias due to attrition. Additionally, proteinuria may be a sign of shared risk factors for vascular disease and chronic kidney disease. The association between proteinuria and stroke may contributed by multiple effect. Specific diseases such as chronic glomerulonephritis cannot be simply ruled out. Urine protein change over time can be an indicator for the severity of those stroke risk factors. Because observational study is unable to determine causality in its findings, whether changes in proteinuria are a risk factor or treatment target needs more exploration. 5 CONCLUSIONS In conclusion, we emphasized that changes in proteinuria, particularly persistent proteinuria, were significantly associated with incident stroke in participants with hypertension. Our study provides valuable information to public health and medical professionals by examining a dynamic relationship between changes in proteinuria and incident stroke in the hypertensive population. 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10 774 WANG et al. 30. Levin A, Stevens PE. Summary of KDIGO 2012 CKD Guideline: behind the scenes, need for guidance, and a framework for moving forward. Kidney Int. 2014;85: SUPPORTING INFORMATION How to cite this article: Wang A, Dai L, Su Z, et al. Proteinuria and risk of stroke in patients with hypertension: The Kailuan cohort study. J Clin Hypertens. 2018;20: org/ /jch Additional Supporting Information may be found online in the supporting information tab for this article.