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Harrison TG, Tonelli M. Measuring albuminuria or proteinuria: does one answer fit all? Kidney Int 2023; 104:904-909. [PMID: 37652205 DOI: 10.1016/j.kint.2023.08.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Revised: 07/30/2023] [Accepted: 08/11/2023] [Indexed: 09/02/2023]
Abstract
Measurement of proteinuria is critical for diagnosing and monitoring kidney disease. A variety of measures are available to clinicians and can identify all urinary proteins (proteinuria) or urine albumin alone (albuminuria). Proteinuria and albuminuria can be measured in either a random urine sample or a timed urine collection (often over 24 hours). Although an international guideline advocates the use of the urinary albumin-to-creatinine ratio for most purposes, this measure is not universally available worldwide and historically has been more costly than alternatives. In addition, there may be important differences in accuracy between the albumin-to-creatinine ratio and others based on magnitude of albuminuria, sex, and certain clinical contexts. In this mini review, we review recommendations from international guidelines and discuss specific contexts where the optimal measure of proteinuria is unclear and, in some situations, controversial. We discuss the evidence supporting current recommendations for choice of measure, including the clinical settings of glomerulonephritis, transplantation, and pregnancy. We also discuss how patient sex and cost may impact this decision.
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Affiliation(s)
- Tyrone G Harrison
- Department of Medicine, University of Calgary, Calgary, Alberta, Canada; Department of Community Health Sciences, University of Calgary, Calgary, Alberta, Canada; O'Brien Institute for Public Health, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Marcello Tonelli
- Department of Medicine, University of Calgary, Calgary, Alberta, Canada; Department of Community Health Sciences, University of Calgary, Calgary, Alberta, Canada; O'Brien Institute for Public Health, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
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Oblak M, Mlinšek G, Kojc N, Frelih M, Buturović-Ponikvar J, Arnol M. Spot Urine Protein Excretion in the First Year Following Kidney Transplantation Associates With Allograft Rejection Phenotype at 1-Year Surveillance Biopsies: An Observational National-Cohort Study. Front Med (Lausanne) 2021; 8:781195. [PMID: 34869503 PMCID: PMC8635090 DOI: 10.3389/fmed.2021.781195] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2021] [Accepted: 10/13/2021] [Indexed: 11/13/2022] Open
Abstract
Introduction: Urine protein excretion is routinely measured to assess kidney allograft injury, but the diagnostic value of this measurement for kidney transplant pathology remains unclear. Here we investigated whether spot urine protein excretion in the first year following transplantation associates with allograft rejection phenotype at 1-year surveillance biopsies and de-novo occurrence of donor-specific antibodies (DSA). Patients and Methods: This prospective, observational national-cohort study included 139 non-sensitized patients who received a deceased donor kidney transplant between December 2014 and 2018. All patients received basiliximab induction and tacrolimus-based immunosuppression. Estimated protein excretion rate (ePER) was calculated monthly from spot urine protein-to-creatinine ratios. At 1-year, all recipients underwent surveillance graft biopsy and were screened for de-novo DSA. Screening-positive sera were subjected to single antigen bead (SAB) testing. The occurrence of de-novo DSA was determined based on SAB reactivity patterns using a mean fluorescence intensity threshold >1,000. Results: Among the 139 study patients, 27 patients (19%) had histologic evidence of T cell-mediated rejection (TCMR), and 9 patients (7%) had histologic evidence of antibody-mediated rejection (AMR) at 1-year surveillance biopsy. One year after transplant, 19 patients (14%) developed de-novo DSA. Compared with patients without rejection and no de-novo DSA, mixed-effects linear regression analysis showed a significant difference in slope of ePER during the first year in patients with AMR and de-novo DSA at 1-year (46, 95% CI 25-68 mg/day/1.73 m2 per month and 34, 95% CI 20-49 mg/day/1.73 m2 per month, respectively). Patients with vascular TCMR also showed a significant difference in ePER slope over time compared with patients with non-rejection findings (31, 95% CI 9-52 mg/day/1.73 m2 per month). The discriminatory power of ePER for intragraft rejection processes was better in patients with AMR (AUC 0.95, 95% CI 0.90-0.99; P < 0.001) than in those with TCMR (AUC 0.68, 95% CI 0.59-0.79; P = 0.002), with 89% sensitivity and 93% specificity for proteinuria >550 mg/day/1.73m2. Conclusions: An increase in ePER in the first year following kidney transplantation associates with AMR, vascular TCMR and de-novo DSA at 1-year and may be used as a non-invasive clinical marker of intragraft endothelial cell injury.
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Affiliation(s)
- Manca Oblak
- Department of Nephrology, University Medical Centre Ljubljana, Ljubljana, Slovenia.,Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
| | - Gregor Mlinšek
- Department of Nephrology, University Medical Centre Ljubljana, Ljubljana, Slovenia.,Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
| | - Nika Kojc
- Faculty of Medicine, Institute of Pathology, University of Ljubljana, Ljubljana, Slovenia
| | - Maja Frelih
- Faculty of Medicine, Institute of Pathology, University of Ljubljana, Ljubljana, Slovenia
| | - Jadranka Buturović-Ponikvar
- Department of Nephrology, University Medical Centre Ljubljana, Ljubljana, Slovenia.,Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
| | - Miha Arnol
- Department of Nephrology, University Medical Centre Ljubljana, Ljubljana, Slovenia.,Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia
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