Comparison of the Kynurenine/Tryptophan Ratio with the Beck Suicide Intent Scale in Patients Admitted to the Emergency Department Due to Suicide Attempt

<b>Objective:</b> Suicide is a major public health problem with multiple biological and psychosocial determinants. Although the kynurenine/tryptophan (KYN/TRP) pathway has been implicated in the neurobiology of suicidal behavior, clinical findings remain inconsistent. This study aimed to evaluate serum tryptophan, kynurenine, and the KYN/TRP ratio in patients presenting to the emergency department after a suicide attempt and to examine their association with suicide risk. <b>Methods:</b> This prospective, cross-sectional, and comparative study was conducted between November 2024 and June 2025 in the Emergency Department of Konya City Hospital. A total of 120 participants were enrolled, including 60 suicide attempt cases and 60 healthy controls. Serum tryptophan and kynurenine levels were measured using the ELISA method, and the KYN/TRP ratio was calculated in molar units. The Beck Suicide Intent Scale (SIS) was administered to the case group. Group comparisons and correlation analyses were performed using appropriate statistical tests, and effect sizes with 95% confidence intervals were reported. <b>Results:</b> Compared with controls, patients showed significantly lower levels of tryptophan (median 35.4 vs. 54.4; <i>p</i> = 0.002), kynurenine (median 1534.5 vs. 2384.0; <i>p</i> < 0.001), and the KYN/TRP ratio (40.9 ± 16.2 vs. 48.8 ± 20.8; <i>p</i> = 0.02). No significant correlations were found between SIS scores and tryptophan (<i>p</i> = 0.180), kynurenine (<i>p</i> = 0.668), or the KYN/TRP ratio (<i>p</i> = 0.246). Subgroup analyses based on psychiatric history or psychiatric consultation recommendations also revealed no significant differences. <b>Conclusions:</b> Serum tryptophan, kynurenine, and the KYN/TRP ratio were significantly reduced in patients with suicide attempts compared to healthy controls. However, these biochemical parameters were not associated with SIS scores. Our findings suggest that tryptophan, kynurenine, and the KYN/TRP ratio may serve as complementary biomarkers but cannot replace clinical and psychometric assessments. Larger, multicenter, and longitudinal studies are needed to clarify their potential clinical value.