Background: Hereditary antithrombin deficiency (HAD) is an uncommon high-risk thrombophilia. Heterozygotes carriers usually present with a first thrombotic event before age 30 mainly venous thrombosis (VT).

Aims: We designed a national HAD registry to collect clinical, laboratory, and treatment data of patients with HAD with the goal of optimizing their management.

Methods: Ongoing prospective HAD registry (ATHN12) created in 2020 to identify a cohort of 100 adults and pediatric patients with HAD followed at thrombosis centers affiliated with the American Thrombosis Hemostasis Network. We collected demographics, laboratory data, thrombosis risk factors, thrombotic events, pregnancies and procedures, antithrombotic therapy, and use of antithrombin concentrate.

Results: 52 patients were identified: 67% females; mean age 35.5 years; 54% had type 1 HAD. There were 67 VT and 3 arterial thrombosis. 65% patients had at least 1 VT and 53% recurrent events. The most common thromboses were lower extremity DVT (52%) and pulmonary embolism (31%) (Table 1). Anticoagulation was prescribed in 97% of patients with VT: 30% direct oral anticoagulants (DOACs), 31% warfarin, and 39% LMWH or UFH (Table 2).

There were 69 pregnancies in 27 women; of these, 9 had first trimester spontaneous abortions and one third trimester fetal loss. Overall there were 46.4% pregnancy complications (Table 2). LMWH was prescribed in 49% pregnancies. There were 6 pre-term deliveries ( < 37 weeks’ gestation). Antithrombin concentrate was administered in 29% pregnancies before delivery. Anticoagulation was continued in 45% of women post-delivery and in 14% anticoagulation was switched to warfarin or DOAC. 79% patients had a total of 108 procedures. Overall, 40% patients received AT concentrate without any adverse events.

Conclusion(s): Recurrent VT was the most common presentation. DOACs and warfarin were equally prescribed in these patients. LWMH was only prescribed in half of the pregnancies and AT concentrates in less than one third of deliveries without adverse events.

Table 1

Patient Baseline Characteristics N&#3f52

Table 2

Anticoagulant Therapy, Antithrombin concentrates, Pregnancies and Procedures

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/athndataset-hereditary-antithrombin-deficiency-had-pilot-project-athn-12-registry-from-the-american-thrombosis-and-hemostasis-network-athn/