Unusual pattern of thrombotic events in young adult non-critically ill patients with COVID-19 may result from an undiagnosed inherited and acquired form of thrombophilia.

In 145 previously healthy non-critically ill young adults, coronavirus disease 2019 (COVID-19)-related symptoms, risk factors for thrombosis, coagulation and inflammatory parameters were compared, with 29 patients reporting unusual thrombotic events (UTEs) and 116 not having thrombotic events. The inflammatory indices, coagulation and prothrombotic platelet phenotype (PTPP) were significantly higher in patients with UTEs versus those without. Patients with UTEs were categorised according to detection of thrombophilic genes (TGs), coagulation and inflammatory markers to the non-TG and TG subcohort. A total of 38 UTEs were identified, which included splanchnic vein thrombosis (SVT; 11), stroke (six), cerebral vein thrombosis (five), thrombotic microangiopathy (four), limb ischaemia and inferior vena cava thrombosis (three each), ST-segment elevation myocardial infarction (two), superior vena cava thrombosis (two), upper limb deep venous thrombosis and retinal vein thrombosis, one each. We found a 55% prevalence of TGs mainly heterozygous coagulation factor II, thrombin (FII)-G20210A, Janus kinase 2 (JAK2)-V617F, protein-S, and antithrombin III deficiency with a high (76·9%) prevalence of venous UTEs, multiple vessels thrombosis, and recurrence rate among the TG versus non-TG subcohort. The presence of JAK2-V617F, and FII-G20210A mutations was linked with SVT. Thrombosis in the non-TG subcohort was associated with more haemorrhagic problems, thrombosis progression and a significantly higher level of inflammatory markers, PTPP, mean platelet volume, von Willebrand factor, and factor VIII, which remained high for up to 6 months, as well as elevated D-dimer. Acquired and inherited thrombophilia with endotheliopathy appeared to be a relevant mechanism to explain the occurrence of UTEs that are not correlated to COVID-19 severity.