doi:10.11613/BM.2026.020701engMartinez-Marzo, EvaPeran, MariaLerma-Irureta, JuanMedel-Martinez, AnaPaules, CristinaOros, DanielFabre, MartaUrinary placental growth factor stability as a critical factor in the reliability of preeclampsia diagnosisART-2026-148988Introduction: Placental growth factor (PlGF) is a key biomarker for diagnosing and predicting preeclampsia (PE). While serum-based PlGF assays are well established, urine has emerged as a promising non-invasive alternative matrix. However, the absence of urinary PlGF stability data remains a major preanalytical limitation. This study aimed to assess urinary PlGF stability under common preanalytical conditions, including refrigerated storage and a double freeze-thaw cycle. Materials and methods: A prospective study was conducted using urine samples from ten pregnant women. Each sample was processed under standard laboratory conditions and aliquoted into five tubes. One aliquot was immediately frozen at - 80 °C (T0), three were stored at 2-8 °C for 48, 96, and 168 hours before freezing, and one underwent a double freeze-thaw cycle. Urinary PlGF concentrations were measured using the Elecsys PlGF immunoassay on Roche Cobas e801 analyzer. Percent degradation (PD%) was calculated relative to baseline. A linear regression model was applied to estimate the time to exceed a maximum permissible instability (MPI) of ± 10 %. Results: Urinary PlGF remained stable at 2-8 °C for up to 48 hours, with a mean PD% of - 6 % (95% confidence interval (CI): - 9.1 to - 2.8). The regression model (PD% = - 0.0834 x Time (h)) estimated the - 10 % threshold at approximately 120 hours. After a double freeze-thaw cycle, the mean PD% was - 1.5 % (95% CI: - 3.4 to 0.4%). Conclusions: Urinary PlGF shows acceptable stability for up to 48 hours under refrigeration and is stable over two freeze-thaw cycles. These findings provide essential preanalytical data supporting its potential use in clinical and research settings.2026http://zaguan.unizar.es/record/17092310.11613/BM.2026.020701http://zaguan.unizar.es/record/170923oai:zaguan.unizar.es:170923info:eu-repo/grantAgreement/ES/DGA/B46-20Rinfo:eu-repo/grantAgreement/ES/DGA/B46-23Rinfo:eu-repo/grantAgreement/ES/ISCIII-FEDER/CM22-00045nfo:eu-repo/grantAgreement/ES/ISCIII/FI21-00224info:eu-repo/grantAgreement/ES/ISCIII/PI22-143Biochemia medica 36, 2 (2026), [9 pp.]byhttps://creativecommons.org/licenses/by/4.0/deed.esinfo:eu-repo/semantics/openAccess