Cross-classification of microalbuminuria and reduced glomerular filtration rate: associations between cardiovascular disease risk factors and clinical outcomes

Background: Chronic kidney disease is defined by reduced estimated glomerular filtration rate (reduced eGFR) or by microalbuminuria (MA). Concordance between reduced eGFR and MA and associated cardiovascular disease (CVD) and all-cause mortality according to these definitions is uncertain.

Methods: Participants (n = 2966 [52.6% were women], mean age, 59 years) were drawn from the Framingham Offspring Cohort. Participants were classified into 4 groups based on the presence or absence of reduced eGFR (eGFR < 59 mL/min/1.73 m(2) in women, < 64 mL/min/1.73 m(2) in men or MA (spot urinary albumin to creatinine ratio of at least 30 mg/g). Cox proportional hazard models were used to determine the combined risk of CVD events and all-cause mortality for each group.

Results: Of the participants, 9.9% (n = 295) had reduced eGFR, and 12.2% (n = 362) had MA. Among those with reduced eGFR, 28% had MA. Those with reduced eGFR and with MA were at increased risk for combined CVD and all-cause mortality compared with those with neither condition (hazard ratio [HR] 1.7, 95% confidence interval [CI], 1.1-2.4; P = .009), whereas those with reduced eGFR and without MA and those without reduced eGFR and with MA had similar HRs (1.3 and 1.2, respectively). Those with reduced eGFR and with MA, as well as those with reduced eGFR and without MA, were at significantly increased risk of all-cause mortality (HR 2.2 [95% CI, 1.4-3.6] and HR 1.7 [95% CI, 1.1-2.6], respectively).

Conclusions: Reduced eGFR and MA are relatively common conditions with different risk factor profiles. The coexistence of reduced eGFR and MA was present in 2.8% of the study sample and conferred substantial increased risk for CVD and all-cause mortality, in part because of a heavy burden of CVD risk factors.