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

Abstract

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 -20.1% and -37.5% in CRIC and DCCT, respectively, whereas that of eAER was +3.8% and -9.7%. 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.

Keywords: Albuminuria; albumin-creatinine ratio (ACR) correction; chronic kidney disease; creatinine; creatinine excretion rate (CER) prediction; proteinuria; urine albumin-creatinine ratio.