Estimated Albumin Excretion Rate Versus Urine Albumin-Creatinine Ratio for the Estimation of Measured Albumin Excretion Rate: Derivation and Validation of an Estimated Albumin Excretion Rate Equation

Background: Glomerular filtration rate estimation equations use demographic variables to account for predicted differences in creatinine generation rate. In contrast, assessment of albuminuria from urine albumin-creatinine ratio (ACR) does not account for these demographic variables, potentially distorting albuminuria prevalence estimates and clinical decision making. Study Design: Polynomial regression was used to derive an age-, sex-, and race-based equation for estimation of urine creatinine excretion rate, suitable for use in automated estimated albumin excretion rate (eAER) reporting. Setting & Participants: The MDRD (Modification of Diet in Renal Disease) Study cohort (N = 1,693) was used for equation derivation. Validation populations were the CRIC (Chronic Renal Insufficiency Cohort; N = 3,645) and the DCCT (Diabetes Control and Complications Trial; N = 1,179). Index Test: eAER, calculated by multiplying ACR by estimated creatinine excretion rate, and ACR. Reference Test: Measured albumin excretion rate (mAER) from timed 24-hour urine collection. Results: eAER estimated mAER more accurately than ACR; the percentages of CRIC participants with eAER within 15% and 30% of mAER were 33% and 60%, respectively, versus 24% and 39% for ACR. Equivalent proportions in DCCT were 52% and 86% versus 15% and 38%. The median bias of ACR was 220.1% and 237.5% in CRIC and DCCT, respectively, whereas that of eAER was 13.8% and 29.7%. Performance of eAER also was more consistent across age and sex categories than ACR. Limitations: Single timed urine specimens used for mAER, ACR, and eAER. Conclusions: Automated eAER reporting potentially is a useful approach to improve the accuracy and consistency of clinical albuminuria assessment. (c) 2014 by the National Kidney Foundation, Inc.