COVID-19 and multisystem inflammatory syndrome in children (MIS-C) are associated with a risk of hypercoagulability and thrombotic events. We aimed (a) to evaluate the demographic, clinical, and laboratory findings as well as the incidence of thrombotic events of COVID-19 and MIS-C in children and (b) to determine the role of antithrombotic prophylaxis.

A single-center retrospective study evaluated hospitalized children with COVID-19 or MIS-C.

The study group consisted of 690 patients, 596 (86.4%) diagnosed with COVID-19 and 94 (13.6%) diagnosed with MIS-C. Antithrombotic prophylaxis was used for 154 (22.3%) patients: 63 patients (10.6%) in the COVID-19 group and 91 (96.8%) patients in the MIS-C group. Use of antithrombotic prophylaxis was statistically higher in the MIS-C group (p<0.001). Patients who received antithrombotic prophylaxis were of older median age, were more commonly male, and had more frequent underlying diseases than those without prophylaxis (p<0.001, p<0.012, p<0.019, respectively). The most common underlying condition was obesity in patients who received antithrombotic prophylaxis. Thrombosis was observed in one (0.2%) patient in the COVID-19 group with a thrombus in the cephalic vein, two (2.1%) patients in the MIS-C group, with a dural thrombus in one patient and a cardiac thrombus in the other patient. The patients with thrombotic events were previously healthy and had mild disease.

In our study, thrombotic events were rare compared with previous reports. We used antithrombotic prophylaxis for most children with underlying risk factors; perhaps for this reason, we did not observe thrombotic events in children with underlying risk factors. We suggest that patients diagnosed with COVID-19 or MIS-C be closely monitored for thrombotic events.