Introduction: A sizeable minority of commercially available blood glucose monitoring (BGM) systems fail to satisfy regulatory accuracy requirements, such as ISO 15197:2013, after approval. This study assessed whether the BGMs tested could consistently meet these ISO requirements by investigating their accuracy in a non-standardized setting., Methods: In this 18-month post-market performance study, using the ISO criteria, healthcare professionals tested the accuracy of four CE-marked BGM systems (Roche Diabetes Care, Mannheim, Germany) on European adults with diabetes mellitus. ISO criteria included 95% of blood glucose (BG) values being within ± 15 mg/dl of a reference measurement for BG < 100 mg/dl or ± 15% for BG ≥ 100 mg/dl and, in the Parkes Consensus Error grid for type 1 diabetes comparing capillary BGM measurements versus reference method, 99% of BG values falling within zone A (no effect on clinical action or outcome) and zone B (altered clinical action with little or no effect on clinical outcome)., Results: BGM readings were obtained from 1650 participants, and the number of readings per BGM system was between 1712 and 2376. The percentage of BGM readings that fell within ISO 15197:2013 limits ranged from 99.4 to 99.9%. For all meter types, 100% of data points fell within zone A or zone B, and most data points for each meter (≥ 99.9%) were in zone A., Conclusion: All four CE-marked BGM models showed results within the accuracy limits defined by ISO 15197 in a non-standardized setting and thus consistently met regulatory accuracy requirements., Competing Interests: Declarations Conflict of interest Julia K. Mader is a member of advisory boards of Abbott Diabetes Care, Becton-Dickinson, Boehringer Ingelheim, Eli Lilly, Embecta, Medtronic, NovoNordisk A/S, Roche Diabetes Care, Sanofi-Aventis, and Viatris. She has received speaker honoraria from A. Menarini Diagnostics, Abbott Diabetes Care, AstraZeneca, Boehringer Ingelheim, Dexcom, Eli Lilly, Medtrust, MSD, NovoNordisk A/S, Roche Diabetes Care, Sanofi, Servier, Viatris, and Ypsomed. Julia K. Mader is a shareholder of decide Clinical Software GmbH and elyte Diagnostics and serves as CMO of elyte Diagnostics. Annette Baumstark is an employee of the Institut für Diabetes-Technologie, Forschungs- und Entwicklungsgesellschaft mbH an der Universität Ulm (IfDT), which carries out clinical studies, for example, with medical devices for diabetes therapy on its own initiative and on behalf of various companies. Johannes Tüting and Günter Sokol have no conflicts of interest to declare. Robbert J. Slingerland is chair of the Clinical Chemistry Department of Isala, which carries out clinical studies, for example, with medical devices for diabetes therapy on its own initiative and on behalf of various companies. Robbert J. Slingerland has received speakers’ honoraria or consulting fees in the last three years from Roche and Menarini. Ruth Schuebel, Yuhong Tong, and Julia Roetschke are employees of Roche. Ethical Approval The study protocol was approved by the appropriate health authorities according to local guidelines and by an Institutional Review Board/Independent Ethics Committee. The Ethics Committees included: Ethikkommission of the State Medical Association of Baden-Wuerttemberg, Stuttgart (AZ MP-2018-10) for the center in Ulm, Germany; and the Ethikkommission of the Medical Association of Lower Saxony, Hanover (AZ Bo/05/2018) for the center in Cloppenburg, Germany. Approval for conducting the study at the centers in Vienna and Graz in Austria was given by the Austrian Agency for Health and Food Safety (AGES). Study approval for the center in Zwolle, The Netherlands, was given by the local authority. The study was conducted in accordance with the Declaration of Helsinki of 1964 and its later amendments. Study participants provided written informed consent., (© 2024. The Author(s).)