1. Details of the dose, type of medication used and length of follow‐up.

Study ID	UFH	Number of participants	Dose	LMWH	Number of participants	Dose	Treatment duration	Time point when plasma samples were obtained for HIT‐IgG antibodies test	Laboratory test for HIT
Warkentin 2003	Standard calcium heparin	192	7500 U sc twice daily	Enoxaparin	170	30 mg sc twice daily	Started 12 h‐24 h after surgery and continued for 14 days or until discharge if it occurred sooner	At least 1 plasma sample obtained on postoperative day 7 or later	SRA, with confirmatory investigation for the presence of functional antibodies of IgG class
Lubenow 2010a	Standard UFH	289	5000 U SC 3 times daily	Certoparin	272	3000 anti‐factor Xa U sc once daily	Started immediately after admission and continued until day 10 or until discharge. After day 10 all participants received LMWH	Obtained on admission, at discharge (if before day 10) and between days 10 and 14	Anti‐platelet factor 4/heparin for immunoglobulin IgG class and platelet‐activating antibodies in the HIPA test
PROTECT 2011	Standard UFH	238	5000 U sc twice daily	Dalteparin	237	5000 U once daily	At least 5 days of heparin in the ICU	Data were collected daily in the ICU	Commercially available platelet factor 4 ELISA and SRA

ELISA: enzyme‐linked immunosorbent assay
 HIPA: heparin‐induced platelet activation
 h: hours
 HIT: heparin‐induced thrombocytopenia
 ICU: intensive care unit
 LMWH: low molecular weight heparin
 mg: milligrams
 sc: subcutaneously
 SRA: serotonin release assay
 U: units
 UFH: unfractionated heparin