Other Patients With COVID and Possible HIT
We encountered 4 additional patients admitted to our ICU with a diagnosis of acute respiratory distress syndrome secondary to COVID-19 infection with thrombocytopenia, and an intermediate to high pretest probability for HIT. Due to a positive platelet factor 4 (PF4) antibody, they were started on an argatroban, pending send out results of OD levels and functional assay. However, the SRA was negative. Interestingly, their clinical characteristics (reported in Table 1) were similar to those of our patients with true HIT. Two of these patients had a confirmed deep vein thrombosis, and one with suspected pulmonary embolism. Also, 2 patients met International Society on Thrombosis and Haemostasis criteria for disseminated intravascular coagulation (DIC). All the patients were in hypotensive shock, requiring vasopressor support.
Table 1.  Characteristics of Patients Who Tested Positive for PF4 Antibody.
Characteristics  Patient 1a  Patient 2  Patient 3  Patient 4  Patient 5
Age in years  63  53  63  70  46
Sex  Male  Male  Male  Female  Female
Indication for anticoagulation  DVT  Acute coronary syndrome and atrial fibrillation  DVT  DVT  Suspected PE
Confirmed thrombosis via imaging  Yes  No  Yes  Yes  No
Days from initiation of heparin to drop in platelets  11  7  6  8  2
4T score  6  5  7  7  4
PF4 antibody (optical density)  Positive (1.243)  Positive (0.707)  Positive (0.767)  Positive (0.042)  Positive (0.307)
Serotonin release assay  Positive  Negative  Negative  Negative  Negative
Presence of DIC by ISTH criteria  No  No  No  Yes  Yes
Abbreviations: DVT, deep vein thrombosis; PE, pulmonary embolism; PF4, platelet factor 4; DIC, disseminated intravascular coagulation; ISTH, International Society on Thrombosis and Haemostasis; HIT, heparin-induced thrombocytopenia.
a  Patient 1 had true HIT. Patients 2 to 5 had false-positive HIT antibody.