Thrombotic microvascular injury is not mediated by thrombotic microangiopathy despite systemic complement activation in Covid-19 patients

Hypoxemia and coagulopathy are common in severe symptomatic patients of coronavirus disease 2019 (COVID-19). Histological evidence shows implication of complement activation and lung injury. We research sign of complement activation and presence of thrombotic microangiopathy in 8 severe patients. Six of them presented moderate elevation of final pathway of complement – sC5b-9 (median value : 350 ng/mL [IQR : 300,5 - 514,95 ng/mL]). Two patients have been autopsied and presence of thrombotic microvascular injury have been found. Interestingly, none the 8 patients had signs of mechanical hemolytic anemia (median value of hemoglobin : 10,5 gr/dL[IQR : 8,1 - 11,9], median value of haptoglobuline 4,49 [IQR 3,55-4,66], none of the patients has schistocyte) and thrombocytopenia (median value: 348000/mL [IQR : 266 000 - 401 000). Finally, all 8 patients had elevated d-dimer (median value : 2226 µgr/l [IQR : 1493 – 2362]) and soluble fibrin monomer complex (median value : 8.5 mg/mL, IQR[<6 – 10.6]). In summary, this study show moderate activation of complement and coagulation with presence of thrombotic microvascular injury in patients with severe COVID-19 without evidence of systemic thrombotic microangiopathy.