Abstract
Functional antithrombin (AT) deficiency is an inherited thrombophilic disorder that can present as venous thrombosis at atypical sites. We report the case of a 47‐year‐old man with a family history of venous thromboembolism who presented with thrombosis involving the splenoportal confluence and the superior mesenteric vein. Initial laboratory evaluation revealed normal AT activity levels and a negative standard thrombophilia panel. Due to the unusual thrombotic location and family history, extended genetic testing was performed, which identified a pathogenic heterozygous variant in
SERPINC1
NM_000488.3:c.749C > A (p.Thr250Asn), consistent with functional AT deficiency. After the resolution of gastrointestinal bleeding complications, long‐term anticoagulation therapy was reintroduced. This case underscores the importance of considering hereditary thrombophilia in patients with thrombosis at unusual sites even when standard laboratory studies are unremarkable.