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Spot urine protein/creatinine ratio (PCR) is often used clinically to estimate 24-hour (24-h) proteinuria. However, urine PCR shows considerable hour to hour variability.1 ,2 In lupus nephritis (LN), spot PCR reveals this variability, while longer timed collections conceal it.3–5 Spot PCR performs well in cohort studies, where its variability is mitigated by averaging the data.6 However, spot PCR variability becomes a liability for individual patient management. This work is the first to compare spot PCR variability in LN and chronic kidney disease (CKD).
For LN, we used the published works (N=3, 165 patients) that documented the completeness (creatinine content) of the 24-h urine collections3–5 (LN studies A, B, and C, respectively). For CKD, we used a standard CKD cohort (ramipril efficacy in nephropathy (REIN) Trial, 98 patients), which documented completeness of the collections.6 Almost all spot PCRs were from morning collections.
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Correction notice This article has been corrected since it was published Online First. The affiliations for Roger Rodby and Giuseppi Remuzzi have been corrected.
Contributors GS, AP, DF, RR, GR, MP, BHR and LAH were involved in patient recruitment and follow-up. DJB, GS and MB were responsible for data collection. DJB, PH and LAH were responsible for data analysis. DJB and LAH wrote the manuscript.
Funding This study was supported in part by the Johns Hopkins University School of Medicine General Clinical Research Center grant M01-RR00052, from the National Center for Research Resources/National Institutes of Health. And by a National Institutes of Health CTSA grant UL1RR025755-01 awarded to The Ohio State University. The Hopkins lupus cohort is supported by the National Institutes of Health AR43727. The Ohio State lupus cohort is supported by the National Institutes of Health P01-DK55546.
Competing interests None.
Ethics approval Institutional Review Board approval.
Provenance and peer review Not commissioned; externally peer reviewed.
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