Non-albuminuric renal impairment is a strong predictor of mortality in individuals with type 2 diabetes: the Renal insufficiency and cardiovascular events (RIACE) Italian multicentre study

Aims/hypothesis: Non-albuminuric renal impairment has become the prevailing diabetic kidney disease (DKD) phenotype in individuals with type 2 diabetes and an estimated GFR (eGFR) <60 ml min−1 1.73 m−2. In the present study, we compared the rate and determinants of all-cause death in individuals with this phenotype with those in individuals with albuminuric phenotypes. Methods: This observational prospective cohort study enrolled 15,773 individuals with type 2 diabetes in 2006–2008. Based on baseline albuminuria and eGFR, individuals were classified as having: no DKD (Alb−/eGFR−), albuminuria alone (Alb+/eGFR−), reduced eGFR alone (Alb−/eGFR+), or both albuminuria and reduced eGFR (Alb+/eGFR+). Vital status on 31 October 2015 was retrieved for 15,656 individuals (99.26%). Results: Mortality risk adjusted for confounders was lowest for Alb−/eGFR− (reference category) and highest for Alb+/eGFR+ (HR 2.08 [95% CI 1.88, 2.30]), with similar values for Alb+/eGFR− (1.45 [1.33, 1.58]) and Alb−/eGFR+ (1.58 [1.43, 1.75]). Similar results were obtained when individuals were stratified by sex, age (except in the lowest age category) and prior cardiovascular disease. In normoalbuminuric individuals with eGFR <45 ml min−1 1.73 m−2, especially with low albuminuria (10–29 mg/day), risk was higher than in microalbuminuric and similar to macroalbuminuric individuals with preserved eGFR. Using recursive partitioning and amalgamation analysis, prevalent cardiovascular disease and lower HDL-cholesterol were the most relevant correlates of mortality in all phenotypes. Higher albuminuria within the normoalbuminuric range was associated with death in non-albuminuric DKD, whereas the classic ‘microvascular signatures’, such as glycaemic exposure and retinopathy, were correlates of mortality only in individuals with albuminuric phenotypes. Conclusions/interpretation: Non-albuminuric renal impairment is a strong predictor of mortality, thus supporting a major prognostic impact of renal dysfunction irrespective of albuminuria. Correlates of death partly differ from the albuminuric forms, indicating that non-albuminuric DKD is a distinct phenotype.