BACKGROUND: The assessment of ADAMTS13 factor activity and inhibitor levels was conducted in severe COVID-19 patients as an observational study. RESULTS: A total of 14 patients were included and the average ADAMTS13 activity level at the time of admission was 28.54±30.74% (range 1.83–86.67%) which was reduced compared to controls (88.09±14.77). Nine patients had reduced ADAMTS13 factor activity (<40%) and 77.7% among them had severe deficiency (<10% activity). ADAMTS13 inhibitor was positive (>15 IU/mL) only in two patients and an overall mean value was 8.15±5.8. Elevated D-Dimer and length of hospital stay had significant correlation with ADAMTS13 activity (–0.247 and 0.306 respectively). No features of thrombotic microangiopathy were observed and hence no plasma exchange was performed. CONCLUSION: Reduced ADAMTS13 factor activity without inhibitor development may give a clue to the disease progress in COVID19.

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