• Chetana N Naresh, Andrew Hayen, Alexander Weening, Jonathan C Craig, and Steven J Chadban.
• Department of Renal Medicine, The Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia; Sydney Medical School, University of Sydney, Sydney, Australia.
• Am. J. Kidney Dis. 2013 Dec 1; 62 (6): 1095-101.

BackgroundAccurate quantification of albuminuria is important in the diagnosis and management of chronic kidney disease. The reference test, a timed urinary albumin excretion, is cumbersome and prone to collection errors. Spot urine albumin-creatinine ratio (ACR) is convenient and commonly used, but random day-to-day variability in ACR measurements has not been assessed.Study DesignProspective cohort study of day-to-day variability in spot urine ACR measurements.Setting & ParticipantsClinically stable outpatients (N = 157) attending a university hospital clinic in Australia between July 2007 and April 2010.OutcomesSpot urine ACR variability was assessed and repeatability limits were determined using fractional polynomials.MeasurementsACRs were measured from spot urine samples collected at 9:00 am on consecutive days and 24-hour urine albuminuria was measured concurrently.ResultsPaired ACRs were obtained from 157 patients (median age, 56 years; 60% men; median daily albumin excretion, 226 [range, 2.5-14,000] mg/d). Day-to-day variability was substantial and increased in absolute terms, but decreased in relative terms, with increasing baseline ACR. For patients with normoalbuminuria (ACR < 3 mg/mmol [<27 mg/g]), a change greater than ±467% (0-17 mg/mmol [0-150 mg/g]) is required to indicate a significant change in albuminuria status with 95% certainty; for those with microalbuminuria (ACR of 3-30 mg/mmol [27-265 mg/g]), a change of ±170% (0-27 mg/mmol [0-239 mg/g]) is required; for those with macroalbuminuria (ACR > 30 mg/mmol [>265 mg/g]), a change of ±83% (5-55 mg/mmol [44-486 mg/g]) is required; and for those with nephrotic-range proteinuria (ACR > 300 mg/mmol [>2,652 mg/g]), a change of ±48% (158-443 mg/mmol [1,397-3,916 mg/g]) is needed to represent a significant change.LimitationsThese study results need to be replicated in other ethnic groups.ConclusionsChanges in chronic kidney disease status attributed to therapy or disease progression, when based solely on a change in ACR, may be incorrect unless the potential for day-to-day biological variation has been considered. Only relatively large changes are likely to indicate a change in disease status.Copyright © 2013 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.

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