Liu et al14 suggested that anti-heparin-PF4 antibodies are induced in critical COVID-19 patients, resulting in HIT. However, OD analysis and SRA were not performed in these patients due to limited resources. Our 4 additional patients with COVID-19 were positive for anti-heparin PF4 antibodies. However, they had a negative confirmatory test. Perhaps, their intermediate to high pretest probabilities was partly related to complications from COVID-19 itself (venous thromboembolism, sepsis, multiorgan dysfunction, and DIC), which led to testing for HIT.