Background: In the field of research for new validated surrogate biomarkers of treatment efficacy, disease activity and progression in Multiple Sclerosis (MS), serum neurofilament light-chain (sNFL) are actually the best candidate for MS patient monitoring. However, before they can be implemented in clinical practice, their usefulness as additional red flag routine measure must be demonstrated. To tackle the problem, this real-life cross-sectional study at the Regional Referring Center for Multiple Sclerosis (CRESM) aims to characterize sNFL levels and prevalence of elevated sNFL, according to our age-dependent cut-off values, in a large group of patients with different types of MS and treatment conditions., Methods: 908 serum samples from as many MS patients being admitted at CRESM for diagnostic definition and/or during routinary treatment monitoring were consecutively collected between January 2019 and January 2020. sNFL levels were measured by single molecule array (Simoa™) technology on SR-X instrument using NF-light assays (Quanterix); results were interpreted using previously published cut-off values., Results: Primary and Secondary Progressive MS (PPMS, SPMS) forms demonstrate higher levels and prevalence of elevated sNFL (PPMS= 32 %, SPMS= 21 %) compared to the Relapse and Remitting one (RRMS = 12 %). Besides, naïve samples of RRMS and PPMS subtypes showed higher prevalence of elevated sNFL (RRMS naïve= 31 %, PPMS naïve=67 %) compared to samples from patients treated for more than 12 months (RRMS treat>12m= 9 %, PPMS treat>12m= 19 %); treated SPMS patients demonstrated higher sNFL levels and a prevalence (22 %) of elevated sNFL compared to RRMS treated patients. Focusing on RRMS, no statistical difference was found between groups of patients treated for whatever time (up to or more than 60 months) and with either DMT type (high or low-efficacy DMT). Finally, RRMS patients treated with all DMTs for more than 12 months, with the exception of teriflunomide and alemtuzumab showed a prevalence of elevated sNFL in the range of 5-10 %., Conclusion: in a real-world setting comprising about 1000 MS patients, sNFL quantification was elevated in 5-to-67 % of patients, in different MS forms and treatment conditions. Elevated levels of sNFL must be considered a red-flag suggesting the need of a further clinical monitoring in any circumstance, as it can be indicative of new inflammation, ongoing degeneration or co-morbidities. This study supports the introduction of sNFL quantification in everyday patient management., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Antonio Bertolotto reports financial support was provided by Roche SpA. Antonio Bertolotto reports financial support was provided by Italian Multiple Sclerosis Association. Paola Valentino reports a relationship with Biogen that includes: speaking and lecture fees and travel reimbursement. Paola Valentino reports a relationship with Novartis that includes: speaking and lecture fees and travel reimbursement. Paola Valentino reports a relationship with Roche SpA that includes: speaking and lecture fees and travel reimbursement. Paola Valentino reports a relationship with Merck & Co Inc that includes: funding grants. Paola Valentino reports a relationship with Quanterix Corp that includes: funding grants. Simona Malucchi reports a relationship with Biogen that includes: speaking and lecture fees and travel reimbursement. Simona Malucchi reports a relationship with Merck & Co Inc that includes: speaking and lecture fees and travel reimbursement. Simona Malucchi reports a relationship with Novartis that includes: speaking and lecture fees and travel reimbursement. Simona Malucchi reports a relationship with Roche SpA that includes: speaking and lecture fees and travel reimbursement. Serena Martire reports a relationship with Biogen that includes: board membership, consulting or advisory, speaking and lecture fees, and travel reimbursement. Serena Martire reports a relationship with Novartis that includes: board membership, consulting or advisory, speaking and lecture fees, and travel reimbursement. Antonio Bertolotto reports a relationship with Almirall that includes: board membership, consulting or advisory, and funding grants. Antonio Bertolotto reports a relationship with Bayer that includes: board membership and consulting or advisory. Antonio Bertolotto reports a relationship with Biogen that includes: board membership, consulting or advisory, funding grants, speaking and lecture fees, and travel reimbursement. Antonio Bertolotto reports a relationship with Genzyme Corporation that includes: board membership and consulting or advisory. Antonio Bertolotto reports a relationship with Novartis that includes: funding grants, speaking and lecture fees, and travel reimbursement. Antonio Bertolotto reports a relationship with Sanofi that includes: speaking and lecture fees and travel reimbursement. Antonio Bertolotto reports a relationship with Associazione San Luigi Gonzaga ONLUS that includes: funding grants. Antonio Bertolotto reports a relationship with Fondazione per la Ricerca Biomedica ONLUS that includes: funding grants. Antonio Bertolotto reports a relationship with Mylan Pharmaceuticals Inc that includes: funding grants. Antonio Bertolotto reports a relationship with Italian Multiple Sclerosis Association that includes: funding grants. Rugiada Bottero reports a relationship with Novartis that includes: consulting or advisory. Rugiada Bottero reports a relationship with Sanofi that includes: consulting or advisory. Rugiada Bottero reports a relationship with Merck that includes: consulting or advisory. Alessia Di Sapio reports a relationship with Biogen that includes: consulting or advisory, speaking and lecture fees, and travel reimbursement. Alessia Di Sapio reports a relationship with Novartis that includes: consulting or advisory, speaking and lecture fees, and travel reimbursement. Alessia Di Sapio reports a relationship with Roche that includes: consulting or advisory, speaking and lecture fees, and travel reimbursement. Alessia Di Sapio reports a relationship with Sanofi that includes: consulting or advisory, speaking and lecture fees, and travel reimbursement. Alessia Di Sapio reports a relationship with Alexion that includes: speaking and lecture fees and travel reimbursement. Alessia Di Sapio reports a relationship with Merck that includes: travel reimbursement. Alessia Di Sapio reports a relationship with Genzyme Corporation that includes: travel reimbursement. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)