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Spot PC ratio estimates of 24-hour proteinuria are more unreliable in lupus nephritis than in other forms of chronic glomerular disease
  1. Daniel J Birmingham1,2,
  2. Ganesh Shidham1,
  3. Annalisa Perna3,
  4. Derek M Fine4,
  5. Michael Bissell5,
  6. Roger Rodby6,
  7. Giuseppi Remuzzi3,
  8. Michele Petri4,
  9. Paul Hebert7,
  10. Brad H Rovin1,2,
  11. Lee A Hebert1
  1. 1Department of Internal Medicine, The Ohio State University Medical Center, Columbus, Ohio, USA
  2. 2The Ohio State University Davis Heart and Lung Research Institute, Columbus, Ohio, USA
  3. 3Instituto de Richerche Farmacologiche, Mario Negri, Mario, Bergamo, Italy
  4. 4Department of Medicine, Johns Hopkins School of Medicine, Baltimore, Maryland, USA
  5. 5Department of Pathology, The Ohio State University Medical Center, Columbus, Ohio, USA
  6. 6Rush-Presbyterian Medical Center, Chicago, Illinois, USA
  7. 7University of Washington School of Public Health, Health Services, Washington, USA
  1. Correspondence to Dr Dan Birmingham, The Ohio State University Medical Center, Columbus , OH 43210, USA; Birmingham.1{at}osu.edu and Dr Lee Hebert, The Ohio State University Medical Center, Columbus , OH 43210, USA; Lee.Hebert@osumc.edu

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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.

As shown in the calibration …

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