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      A Simple Equation to Estimate Urinary Flow Rate Using Urine Creatinine

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          Abstract

          Background: Accurate assessment of urine flow remains challenging in both inpatient and outpatient settings. We hypothesized we could derive an equation that would accurately estimate urine flow rate (eV) through derivation from other existing equations commonly used in nephrology clinical practice. Methods: The eV equation was derived using the Cockcroft-Gault and the measured creatinine clearance (CrCl = U<sub>Cr</sub>V/P<sub>Cr</sub>) equations. Within the African American Study of Kidney Disease and Hypertension (AASK; n = 570) and COMBINE ( n = 133) clinical trials, we identified participants with concordant estimated and measured creatinine excretion rates to define a subset with highly accurate 24-h urine collections, to assure a reliable gold standard. We then compared eV to measured 24-h urine flow rates in these trials. Results: In AASK, we found a high correlation between eV and measured urine flow rate (V; r = 0.91, p < 0.001); however, Bland-Altman plots showed that eV was 9.5 mL/h lower than V, on average. Thus, we added a correction factor to the eV equation and externally validated the new equation in COMBINE. eV and V were again highly correlated ( r = 0.91, p < 0.001), and bias was improved (mean difference 5.3 mL/h). Overall, 80% of individuals had eV that was within 20% of V. Conclusions: A simple equation using urine creatinine, demographics, and body weight can accurately predict urine flow rate and may have clinical utility in situations where it is difficult to accurately measure the urine flow rate.

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          Author and article information

          Journal
          AJN
          Am J Nephrol
          10.1159/issn.0250-8095
          American Journal of Nephrology
          S. Karger AG
          0250-8095
          1421-9670
          2020
          May 2020
          09 March 2020
          : 51
          : 5
          : 395-400
          Affiliations
          aDivision of Nephrology-Hypertension, Department of Medicine, University of California San Diego, San Diego, California, USA
          bDepartment of Quantitative Health Sciences, Cleveland Clinic, Cleveland, Ohio, USA
          cRenal Section, Veterans Affairs Pittsburgh Healthcare System, Pittsburgh, Pennsylvania, USA
          dDivision of Nephrology, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
          eVeterans Affairs Salt Lake City Healthcare System, Salt Lake City, Utah, USA
          fDivision of Nephrology and Hypertension, University of Utah, Salt Lake City, Utah, USA
          gDivision of Nephrology and Hypertension, Department of Medicine and Center for Translational Metabolism and Health, Institute for Public Health and Medicine, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA
          hNephrology Section, Veterans Affairs San Diego Healthcare System, La Jolla, California, USA
          iDivision of Preventive Medicine, Department of Family Medicine and Public Health, University of California San Diego, San Diego, California, USA
          Author notes
          *Joachim H. Ix, MD, MAS, Division of Nephrology-Hypertension, University of California San Diego, 3350 La Jolla Village Drive, Mail Code 9111-H, San Diego, CA 92161 (USA), joeix@ucsd.edu
          Article
          506728 Am J Nephrol 2020;51:395–400
          10.1159/000506728
          32150743
          © 2020 S. Karger AG, Basel

          Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

          Page count
          Figures: 5, Tables: 1, Pages: 6
          Categories
          Patient-Oriented, Translational Research: Research Article

          Cardiovascular Medicine, Nephrology

          Kidney disease, Prediction, Creatinine, Urine volume

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