['Recommended management of attacks of hereditary angioedema (HAE) due to C1 esterase inhibitor (C1-INH) deficiency (C1-INH-HAE) includes therapy with exogenous C1INH. Thrombotic/thromboembolic events (TEE) have been reported with plasma-derived C1INH, but so far none with recombinant human C1INH (rhC1INH). This phase III, randomized, placebo (saline)-controlled study evaluated the safety of rhC1INH 50\xa0IU/kg for the treatment of acute attacks in 74 patients with C1-INH-HAE.', 'Monitoring for TEE and assessment of risk of deep vein thrombosis (DVT) by the Wells prediction rule were performed, and levels of fibrin degradation products (plasma D-dimers) were assessed before study drug administration (baseline), 2\xa0h, and 7\xa0days posttreatment.', 'Plasma D-dimer levels were elevated in 80% of the patients (median [25th-75th percentiles]: 2149 [480-5105]\xa0μg/l; normal ≤250\xa0μg/l) and were higher in patients with submucosal (abdominal, oropharyngeal-laryngeal) attacks (3095 [890-10000]\xa0μg/l; n\xa0=\xa029) compared with subcutaneous (peripheral, facial) attacks (960 [450-4060]\xa0μg/l; n\xa0=\xa035). Median plasma D-dimer levels were comparable across treatment groups at baseline (1874 [475-4568]\xa0μg/l rhC1INH; 2259 [586-7533]\xa0μg/l saline) and 2\xa0h postinfusion (2389 [760-4974]\xa0μg/l rhC1INH; 2550 [310-8410]\xa0μg/l saline); median plasma D-dimer levels were decreased by Day 7 in both groups (425 [232-3240]\xa0μg/l rhC1INH; 418 [246-2318]\xa0μg/l saline). No increased risk of DVT was identified, nor any TEE reported in rhC1INH treated or controls.'] Are elevated D-dimers in attacks of hereditary angioedema associated with increased thrombotic risk?