Level of albuminuria and risk of stroke: systematic review and meta-analysis.

BACKGROUND Gross albuminuria is associated with increased stroke risk, but it is unclear whether stroke incidence varies by level of albuminuria. We meta-analyzed prospective cohort studies to investigate the impact of various albuminuria levels and continuous urinary albumin excretion (UAE) change on stroke risk. METHODS Systematic search for studies reporting quantitative estimates of the multivariate-adjusted relative risk (RR) and 95% CI for stroke risk associated with microalbuminuria (UAE 30-300 mg/day or nearest equivalent interval) and macroalbuminuria (UAE >300 mg/day) and studies that analyzed the relation of stroke with UAE continuously. Estimates were combined using a random-effect model. RESULTS We identified seven studies comprising 46,638 participants with 1,479 stroke events. Incident stroke risk was greater for macroalbuminuria (RR 2.65, 95% CI 2.25-3.14) than microalbuminuria (RR 1.58, 95% CI 1.39-1.80), a difference that was significant (p for heterogeneity < 0.001, I(2) = 96%). In addition, risk of stroke increased proportionally with rising UAE (p < 0.001), even for UAE within normal range (beginning from levels as low as 2-4 mg/g). CONCLUSIONS Higher albuminuria level confers greater stroke risk. These findings provide additional weight to evidence that albuminuria is strongly linked to stroke risk, and suggest that persons with elevated UAE levels may especially benefit from more intensive vascular risk reduction.