Albuminuria, impaired kidney function and cardiovascular outcomes or mortality in the elderly

Background. Kidney disease is a risk factor for mortality and cardiovascular disease in older adults, but the separate and combined effects of albuminuria and cystatin C, a novel marker of glomerular filtration, are not known. Methods. We examined associations of these markers with mortality and cardiovascular outcomes during a median follow-up of 8.3 years in 3291 older adults in the Cardiovascular Health Study. Kidney disease was assessed using urinary albumin/creatinine ratio (ACR), cystatin C and Modification of Diet in Renal Disease estimated glomerular filtration rate (eGFR). We defined subgroups based on presence of microalbuminuria (MA, ACR > 30 mg/g) and categories of normal kidney function (cystatin C 60 mL/min/1.73 m2); preclinical kidney disease (cystatin C level > 1.0 mg/l but eGFR > 60 mL/min/1.73 m2); and chronic kidney disease (CKD) (eGFR < 60 mL/min/1.73 m2). Cox proportional hazards models were used to examine associations between these six subgroups and all-cause or cardiovascular mortality, myocardial infarction and heart failure. Results. One thousand one hundred fifty (34.9%) had normal kidney function (12.2% with MA), 1518 (46.1%) had preclinical kidney disease (17.9% with MA) and 622 (18.9%) had CKD (47% with MA). After adjustment, the presence of either preclinical kidney disease or MA was associated with an over 50% increase in mortality risk; the presence of both was associated with a 2.4-fold mortality risk. Those with CKD and MA were at highest risk, with a nearly 4-fold mortality risk. Conclusion. Elevated cystatin C and albuminuria are common, identify different subsets of the older population, and are independent, graded risk factors for cardiovascular disease and mortality.