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Objective: As coronavirus disease 2019 (COVID-19) is frequently associated with thrombotic diseases, the hemostatic abnormalities in cases of COVID-19 have attracted attention. This study examined the hemostatic abnormalities in patients with severe COVID-19.

Methods: Hemostatic abnormalities were examined based on the activated partial thromboplastin time (APTT) and small amount of tissue factor-induced FIX activation (sTF/FIXa) using a clot waveform analysis (CWA). The anti-Xa activity, C5b-9 and ADAMTS 13 values were also examined in these patients.

Results: CWA-APTT and CWA-sTF/FIXa showed that the peak times were prolonged, but peak heights were increased before anticoagulant therapy. The parameters of the CWA-APTT and CWA-sTF/FIXa were not correlated with the anti-Xa activity. The peak times of the CWA-sTF/FIXa were significantly longer in non-survivors than survivors. Although the plasma levels of C5b-9 and ADAMTS13 activity were markedly decreased in severe COVID-19 patients, there were no significant differences in C5b-9 levels or ADAMTS-13 activity between survivors and non-survivors.

Conclusions: The CWA showed the marked hemostatic abnormalities and hypercoagulability in COVID-19 patients, and anticoagulant therapy might not be monitored by routine APTT.