Table 1.

4T's score of heparin-induced thrombocytopenia and thrombosis with laboratory findings and anti-platelet factor 4 antibody.

	Covid-19 Day 9	Covid-19 Day 10	Covid-19 Day 11a	Covid-19 Day 12
Thrombocytopenia: percentage of platelet count fall	0 (fall in platelet count < 30%)	0 (fall in platelet count < 30%)	2 (fall in platelet count > 50%)	2 (fall in platelet count > 50%)
Timing of platelet count fall	0 (no fall of platelet count)	0 (no fall of platelet count)	0 (platelet fall without exposure to heparin in the 100 previous days)	0 (within 24 h after exposure of heparin)
Thrombosis or other clinical events	0 (no event)	0 (no event)	2 (new confirmed acute myocardial infarction)	2 (repeated myocardial infarctions)
Other possible causes of thrombocytopenia	0 (no fall of platelet count)	0 (no fall of platelet count)	2 (no evident explanation for platelet count fall)	2 (no evident explanation for platelet count fall)
4T's score	2	2	6	6
Anti-PF4-heparin antibody (ng/mL)	0.38			17.14
Platelet count (×109/L)	200	215	80	74
D-Dimer (ng/mL)	8.3	N/A	>10.0	>10.0
Prothrombin time (s)	11.8	N/A	40.4	36.0
Activated partial thromboplastin time (s)	40.4	N/A	>100	>100
International normalized ratio	1.1	N/A	4.0	3.6

The item of “timing of platelet count fall” was scored 0, and the 4T's score was 6 at both Covid-19 Days 11 and 12 using the diagnosis guideline of HITT by Gruel Y et al. in 2020.

^aThe blood sample on Covid-19 Day 11 was collected before heparin therapy for extracorporeal membrane oxygenation.