Table 1. Characteristics of included studies.

First author	Publication date	Study design	Country	Multicentre	non-COVID ARDS comparator	Number of COVID ARDS patients	Number of non-COVID ARDS patients	All patients on ECMO	Longest follow-up available	D-dimer data collection time
T. Autschbach [26]	2021	observational, cohort, propensity matched	Germany	no	Influenza A (H1A1)	19	34	yes	90 days	before ECMO
A. J. Doyle [15]	2021	retrospective	UK	no	Influenza	51	80	yes	-	before ECMO
V. Fanelli [17]	2022	retrospective	Italy	yes	H1N1	146	162	yes	90 days	before ECMO
G. Hékimian [18]	2021	prospective, cohort	France	no	severe influenza pneumonia, bacterial pneumonia, sepsis	20	10	yes	on ECMO	before ECMO
J. Helms [19]	2020	prospective and historical prospective cohort	France	yes	bacterial, viral	150	233	no	7 days	at ICU admission
D.J. Hoechter [20]	2020	retrospective	Germany	no	any kind	22	14	no	-	within 48 hours from ICU admission
C. N. Lang [22]	2021	retrospective, observational	Germany	no	any kind	47	116	not all (COVID-ARDS 14/47 vs. non-COVID ARDS 49/116)	ICU stay	at admission
M. Lemzey [21]	2020	retrospective, observational, case-control	France	no	any kind	44	39	no	28 days	at ICU admission
K. A. Northam [24]	2022	retrospective, cohort	USA	no	influenza	31	14	yes	in hospital mortality	during ECMO
L. A. Raff [12]	2022	retrospective	USA	no	influenza	32	28	yes	60 days	before ECMO
B. Seelinger [23]	2022	retrospective	Germany	yes	any kind	142	68	yes	-	before ECMO
M. W.Sjoding [14]	2021	retrospective, cohort	USA	no	any kind	130	382	no	28 days	within 48 hours from intubation
S.Spadaro [25]	2021	prospective	Italy	no	any kind	31	10	no	-	within 48 hours from start of mechanical ventilation
S. Yin [16]	2021	retrospective	China	no	any kind	449	104	no	28 days	at the time the patients met the definition of severe illness
J. Zhang [13]	2021	retrospective	China	yes	non-viral	90	130	no	-	at ICU admission

ARDS = acute respiratory distress syndrome; ECMO = extracorporeal membrane oxygenation; ICU = intensive care unit.