Can methylmalonic acid be used as a surrogate marker of Nitrous Oxide Abuse?

<h3>Introduction</h3> The UK recreational use of nitrous oxide (N2O) has rapidly increased leading to severe neurological sequalae, making this a serious public health concern. A wide range of clinical presentations makes it difficult to estimate the number of users. Methylmalonic acid (MMA) level is part of ABN guidelines for N2O use work up. <h3>Method</h3> Retrospective chart analysis was used to identify MMA requests secondary to N2O use in University Hospitals Birmingham NHS Trust from July 2022 to August 2023. Age, gender, ethnicity and residence of users was collected. <h3>Results</h3> 79 of 215 (35.74%) MMA requests were for N2O users. Other MMA requests were for metabolic disorders, and from specialist neurology clinics for different types of neuropathies and a few other disorders. There appears to be some seasonal variation in requests which may reflect seasonal variations in N2O abuse. As in previous studies, N2O users are predominantly young males of Asian ethnicity. <h3>Conclusion</h3> The data can be used for assisting clinicians, public health and the police in targeting an effective health education response. There may be a reduction in the number of requests in the latter half of 2023 which pre-dates law enforcement and needs to be investigated further.