Albuminuria assessed from first-morning-void urine samples versus 24-hour urine collections as a predictor of cardiovascular morbidity and mortality

Abstract

Screening for albuminuria has been advocated because it is associated with cardiovascular morbidity and all-cause mortality. The "gold standard" to assess albuminuria is 24-hour urinary albumin excretion (UAE). Because 24-hour urine collection is cumbersome, guidelines suggest measuring albuminuria in a first morning void, either as urinary albumin concentration (UAC) or adjusted for creatinine concentration, the albumin:creatinine ratio (ACR). To decide which albuminuria measure to use in clinical practice, it is essential to know which best predicts clinical outcome. In a sample representative of the Groningen (the Netherlands) population (n = 3,414), the authors compared UAC, ACR, and UAE as predictors of cardiovascular events and all-cause mortality. During a median follow-up of 7.5 years, which ended December 31, 2005, they observed 278 events (a major adverse cardiovascular event or mortality). The area under the receiver operating characteristic curve predicting events was 0.65 for UAE, 0.62 for UAC (P = 0.06 vs. UAE), and 0.66 for ACR (P = 0.80 vs. UAE; P = 0.01 vs. UAC). When sex-specific subgroups were considered, UAE was superior to UAC in predicting outcome (P = 0.04) for females, whereas, for males as well as females, no difference was found between ACR and UAE. To predict cardiovascular morbidity and all-cause mortality, measuring ACR in a first-morning-void urine sample is a good alternative to measuring 24-hour UAE.