{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T18:08:26Z","timestamp":1785434906691,"version":"3.56.0"},"reference-count":23,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,4,26]],"date-time":"2026-04-26T00:00:00Z","timestamp":1777161600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000780","name":"European Union","doi-asserted-by":"crossref","award":["101095146"],"award-info":[{"award-number":["101095146"]}],"id":[{"id":"10.13039\/501100000780","id-type":"DOI","asserted-by":"crossref"}]},{"award":["101095146"],"award-info":[{"award-number":["101095146"]}],"id":[{"id":"https:\/\/ror.org\/019w4f821","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>Urinary epidermal growth factor (uEGF) and clusterin (uCLU) are emerging biomarkers in chronic kidney disease (CKD), but rigorous analytical validation is required before clinical implementation. We evaluated intra-individual variability and long-term storage stability of uEGF and uCLU in CKD. In the prospective, multicenter UVALID study, 60 adults with CKD stages 2\u20134 underwent urine sampling at three visits over 8 weeks. First-morning and 24-h urine samples were collected to assess intra-individual variability over 24 h, 3 days and 8 weeks. Biomarkers were measured in duplicate by ELISA and normalized to urinary creatinine (\/Cr). Inter-laboratory performance was assessed using quality control samples. Stability after 12 and 15 months of storage at \u221220 \u00b0C and \u221280 \u00b0C and the influence of pH were evaluated. Over 24 h, 3 days, and 8 weeks, uEGF\/Cr demonstrated low variability and remained stable after long-term storage at both temperatures. In contrast, uCLU\/Cr showed greater variability and pronounced instability at \u221220 \u00b0C, whereas stability was preserved at \u221280 \u00b0C. Samples with pH &gt; 6 partially preserved uCLU stability at \u221220 \u00b0C. Inter-laboratory reproducibility was acceptable for uEGF but suboptimal for uCLU at low concentrations. Thus, uEGF showed robust analytical performance, supporting its potential clinical applicability in CKD, whereas uCLU exhibited important analytical and pre-analytical limitations, warranting further assay optimization. These findings underscore the need for rigorous validation to facilitate biomarker implementation in clinical practice.<\/jats:p>","DOI":"10.3390\/ijms27093838","type":"journal-article","created":{"date-parts":[[2026,4,28]],"date-time":"2026-04-28T11:33:37Z","timestamp":1777376017000},"page":"3838","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Intra-Individual Variability of Urinary EGF and Clusterin, and Effect of Frozen Storage on Stability: Results from UVALID"],"prefix":"10.3390","volume":"27","author":[{"ORCID":"https:\/\/orcid.org\/0009-0003-3983-5136","authenticated-orcid":false,"given":"Erik","family":"Moedt","sequence":"first","affiliation":[{"name":"Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, 9700RB Groningen, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0006-1497-4748","authenticated-orcid":false,"given":"R\u00e9mon","family":"Vos","sequence":"additional","affiliation":[{"name":"Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, 9700RB Groningen, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wenjun","family":"Ju","sequence":"additional","affiliation":[{"name":"Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3356-6791","authenticated-orcid":false,"given":"Stephan J. L.","family":"Bakker","sequence":"additional","affiliation":[{"name":"Department of Internal Medicine, University of Groningen, University Medical Center Groningen, 9700RB Groningen, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9737-795X","authenticated-orcid":false,"given":"Marte O.","family":"Rygg","sequence":"additional","affiliation":[{"name":"Steno Diabetes Center Copenhagen, 2730 Herlev, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peter","family":"Rossing","sequence":"additional","affiliation":[{"name":"Steno Diabetes Center Copenhagen, 2730 Herlev, Denmark"},{"name":"Department of Clinical Medicine, University of Copenhagen, 1165 Copenhagen, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2168-702X","authenticated-orcid":false,"given":"Michele","family":"Provenzano","sequence":"additional","affiliation":[{"name":"Department of Medical and Surgical Sciences (DIMEC), Alma Mater Studiorum-University of Bologna, 40126 Bologna, Italy"},{"name":"Nephrology, Dialysis and Renal Transplant Unit, Department of Pharmacy, Health and Nutritional Sciences, University of Calabria, Rende-Hospital \u2018SS. Annunziata\u2019, 87100 Cosenza, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0220-1653","authenticated-orcid":false,"given":"Lilio","family":"Hu","sequence":"additional","affiliation":[{"name":"Department of Medical and Surgical Sciences (DIMEC), Alma Mater Studiorum-University of Bologna, 40126 Bologna, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5473-8551","authenticated-orcid":false,"given":"Gaetano","family":"La Manna","sequence":"additional","affiliation":[{"name":"Department of Medical and Surgical Sciences (DIMEC), Alma Mater Studiorum-University of Bologna, 40126 Bologna, Italy"},{"name":"Nephrology, Dialysis and Kidney Transplant Unit, IRCCS-Azienda Ospedaliero-Universitaria di Bologna, 40138 Bologna, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1134-9051","authenticated-orcid":false,"given":"Jose L.","family":"Gorriz","sequence":"additional","affiliation":[{"name":"Nephrology Department, Hospital Clinico Universitario de Valencia, INCLIVA Biomedical Research Institute, University of Valencia, 46010 Valencia, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1812-4098","authenticated-orcid":false,"given":"Francesc","family":"Moncho-Franc\u00e9s","sequence":"additional","affiliation":[{"name":"Nephrology Department, Hospital Clinico Universitario de Valencia, INCLIVA Biomedical Research Institute, University of Valencia, 46010 Valencia, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tobias B.","family":"Huber","sequence":"additional","affiliation":[{"name":"III. Department of Medicine, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany"},{"name":"Hamburg Center for Kidney Health, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Maja","family":"Lindenmeyer","sequence":"additional","affiliation":[{"name":"III. Department of Medicine, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany"},{"name":"Hamburg Center for Kidney Health, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3126-3730","authenticated-orcid":false,"given":"Hiddo J. 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Department of Medicine, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany"},{"name":"Hamburg Center for Kidney Health, University Medical Center Hamburg-Eppendorf, 20251 Hamburg, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,4,26]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"786","DOI":"10.1016\/S0140-6736(21)00519-5","article-title":"Chronic kidney disease","volume":"398","author":"Jafar","year":"2021","journal-title":"Lancet"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"e342","DOI":"10.1016\/S2214-109X(24)00050-0","article-title":"The major global burden of chronic kidney disease","volume":"12","author":"Jadoul","year":"2024","journal-title":"Lancet Glob. 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