Kynurenine pathway activation in ectopic pregnancy: diagnostic value of 3-hydroxykynurenine and 3-hydroxyanthranilic acid; a prospective study

Background and Aims: Ectopic pregnancy (EP) is a leading cause of maternal morbidity and mortality in the first trimester, accounting for nearly 9% of pregnancy-related deaths. An accurate biochemical marker for early detection is still unavailable. The kynurenine pathway, the primary route of tryptophan metabolism, is involved in immune tolerance, oxidative stress, and placental development. This study aimed to evaluate kynurenine metabolites as potential biomarkers for EP. Methods: In this prospective single-center study, 106 pregnant women were recruited between January and June 2025, including 53 women with confirmed EP and 53 healthy first-trimester controls. Serum levels of tryptophan and its metabolites [3-hydroxykynurenine (3-HK), 3-hydroxyanthranilic acid (3-HAA), kynurenine, quinolinic acid, and kynurenic acid] were quantified using LC-MS/MS. Group comparisons, correlation analyses, and ROC curve evaluations were conducted. Results: No significant differences were found in tryptophan, kynurenine, quinolinic acid, or kynurenic acid between groups (p > 0.05). However, 3-HK and 3-HAA were significantly elevated in the EP group (p < 0.001). ROC analysis demonstrated good diagnostic accuracy for 3-HAA (AUC = 0.80, 95% CI: 0.71–0.88) and 3-HK (AUC = 0.77, 95% CI: 0.67–0.86). Combined use improved discrimination (AUC = 0.86; sensitivity = 0.85; specificity = 0.75). Additionally, 3-HK correlated negatively with gestational age (ρ=–0.42, p < 0.001) and positively with monocyte and leukocyte counts. Conclusion: These findings suggest that elevated 3-HK and 3-HAA levels are associated with EP and may reflect immunometabolic dysregulation underlying abnormal implantation, rather than implying a causal relationship. Therefore, these metabolites may offer complementary biomarker potential in selected research settings.