Urine Albumin-Creatinine Ratio Versus Albumin Excretion for Albuminuria Staging: A Prospective Longitudinal Cohort Study

Abstract

Background: New guidelines advocate the use of albumin-creatinine ratio (ACR) in a urine sample instead of 24-hour urinary albumin excretion (UAE) for staging albuminuria. Concern has been expressed that this may result in misclassification for reasons including interindividual differences in urinary creatinine excretion.

Study design: Prospective longitudinal cohort study.

Setting & participants: We examined 7,623 participants of the PREVEND and RENAAL studies for reclassified when using ACR instead of 24-hour UAE, the characteristics of reclassified participants, and their outcomes. Albuminuria was categorized into 3 ACR and UAE categories: <30, 30 to 300, and >300mg/g or mg/24 h, respectively.

Predictors: Baseline ACR and 24-hour UAE.

Outcomes: Cardiovascular (CV) morbidity and mortality and all-cause mortality.

Results: When using ACR in the early morning void instead of 24-hour UAE, 88% of participants were classified in corresponding albuminuria categories. 307 (4.0%) participants were reclassified to a higher, and 603 (7.9%), to a lower category. Participants who were reclassified to a higher ACR category in general had a worse CV risk profile compared with nonreclassified participants, whereas the reverse was true for participants reclassified to a lower ACR category. Similarly, Cox proportional hazards regression analyses showed that reclassification to a higher ACR category was associated with a tendency for increased risk for CV morbidity and mortality and all-cause mortality, whereas reclassification to a lower ACR category was associated with a tendency for lower risk. Net reclassification improvement, adjusted for age, sex, and duration of follow-up, was 0.107 (P=0.002) for CV events and 0.089 (P<0.001) for all-cause mortality.

Limitations: Early morning void urine collection instead of spot urine collection.

Conclusions: Our results indicate that there is high agreement between early morning void ACR and 24-hour UAE categories. Reclassification is therefore limited, but when present, is generally indicative of the presence of CV risk factors and prognosis.

Keywords: Albuminuria; PREVEND (Prevention of Renal and Vascular Endstage Disease); RENAAL (Reduction of Endpoints in Non−Insulin-Dependent Diabetes With the Angiotensin II Antagonist Losartan); albumin-creatinine ratio (ACR); albuminuria staging; cardiovascular outcome; mortality; risk categorization; urinary albumin excretion (UAE).