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Objectives Trimethylamine N-oxide (TMAO), a gut microbiota–derived metabolite, is associated with cardiovascular disease (CVD) via pro-inflammatory and pro-atherogenic mechanisms. Systemic lupus erythematosus (SLE) is a systemic autoimmune disease with a significantly increased risk of CVD. Emerging evidence suggests that TMAO may contribute to inflammation and cardiovascular complications in SLE; however, related studies remain limited. This study aimed to assess the clinical significance of TMAO in patients with SLE, including analyses of precursor metabolites and the gut microbiome.Methods In total, 207 participants, including 157 patients with SLE and 50 healthy controls (HC), were enrolled. Serum and fecal samples were collected to measure TMAO and related metabolites. Serum TMAO levels were assessed using enzyme-linked immunosorbent assay (ELISA), and fecal choline, trimethylamine (TMA), TMAO, and dimethylamine (DMA) were quantified by proton nuclear magnetic resonance ( 1H-NMR) spectroscopy. Gut microbiota composition was analyzed through 16S rRNA sequencing.Results Serum TMAO levels did not show a statistically significant difference between patients with SLE and HC (P = 0.396). SLE patients with comorbid CVD had significantly higher TMAO levels than HC (P = 0.028) and SLE patients without CVD (P = 0.004). Serum TMAO (P = 0.025) and fecal TMA (P = 0.032) levels were positively correlated with the Systemic Lupus International Collaborating Clinics/American College of Rheumatology (SLICC/ACR) damage index. Serum TMAO levels were negatively correlated with steroid dose (P = 0.038). Distinct gut microbiota compositions were observed between SLE patients with and without CVD.Abstract PO:03:066 Figure 1Conclusions TMAO is associated with CVD and organ damage in patients with SLE. Steroids are likely linked to reduced TMAO levels, and the gut microbiome may contribute to the underlying mechanisms.