On both platforms, IBD cases had higher plasma levels of prostaglandin-H2 d-isomerase than controls (UKB-BI with Olink: OR = 1.67 per s.d., P = 4.7 × 10−40; Iceland with SomaScan: OR = 1.36 per s.d., P = 1.9 × 10−13), consistent with the reported role of the PGD2 metabolic pathway in IBD supported by animal models23,24. Here, PTGDS is linked to inflammatory bowel disease.