TABLE 1.

Clinical characteristics of studies included in the meta-analysis.

Author (year)	Study design	Age	Male (%)	Total patients	Heparin dose				No AC	Hypertension (%)	Diabetes (%)	Heart failure (%)	Severe Covid (%)
					Not specified	Prophylactic	Intermediate	Full
Albani et al. (2020)	R—cohort	70.4	65.8	1,403	799	—	—	—	604	35.1	19.0	—	—
Ayerbe et al. (2020)	R—cohort	67.6	60.5	2,019	1,734	—	—	—	285	—	—	—	—
Lemos et al. (2020)	RCT	56.5	80.0	20.0	—	10	—	10	—	35.0	35.0	—	100.0a
Bielza et al. (2021)	R—cohort	87.0	35.4	502	502	—	—	-	128	60.4	15.2	10	74.2b
Billett et al. (2020)	R—cohort	—	52.6	3,625	—	1,544	—	163	639	-	-	—	8.6a
Bolzetta et al. (2021)	R—cohort	84.1	38.1	81	—	57	—	24	—	63.0	24.7	3.7	—
Canoglu and Saylan (2020)	R—case control	—	62.3	154	—	98	—	56	—	—	—	—	—
Desai et al. (2020)	R—cohort	64.8	66.1	575	240	—	—	—	335	43.1	20.0		—
Di Castelnuovo et al. (2021)	R—cohort	67.1	61.6	2,574	1,804	—	—	—	770	71.7	28.2	—	—
Falcone et al. (2020)	P—cohort	70.0	76.2	315	244	—	—	—	71	46.0	16.5	—	17.5a
Felldin et al. (2020)	R—cohort	56.0	57.0	53	27	—	—	—	26	54.7	30.2	3.8	32.0c
Ferguson et al. (2020)	R—cohort	63.6	55.3	141	—	95	—	46	—	—	24.1	—	—
Hsu et al. (2020)	R—cohort	60.2	55.3	452	—	377	—	48	27	—	36.9	—	—
Ionescu et al. (2020)	R—cohort	64.5	48.5	3,480	—	2,121	—	998	361	52.1	29.0	7.8	18.5a
Jonmarker et al. (2020)	R—cohort	61.0	82.2	152	—	67	48	37	—	45.4	16.5	—	—
Li et al. (2020)	R—case control	63.8	64.0	71	—	28	—	28	—	68.0	64.0	—	39.0a
Llitjos et al. (2020)	R—cohort	68.0	77.0	26.0	-	8	—	18	—	85.0	—	—	100.0a
Lopes et al. (2021)	RCT	56.6	60.0	615	—	311	—	304	—	49.5	24.5	2.5	6.5
Martínez-Botía et al. (2021)	R—cohort	—	60.0	2,035	342	—	—	—	342	—	—	—	—
d'Arminio Monforte et al. (2020)	P—cohort	60.0	63.0	539	—	355	—	—	184	46.4	17.6	—	48.6d
Motta et al. (2020)	R—cohort	64.7	58,8	374	—	299	—	75	—	—	31.6	—	11.8
Nadeem et al. (2021)	R—case control	50.7	86.6	74	—	34	—	40	—	28.1	47.0	—	81.8
Nadkarni et al. (2020)	R—cohort	65.0	56.0	4,389	—	1,959	—	900	1,530	34.8	22.6	8.3	10.6a
Pesavento et al. (2020)	R—cohort	71.0	55.9	324	—	240	—	84	—	—	—	—	—
Qin et al. (2021)	P—cohort	60.0	48.0	749	—	109	—	77	—	—	—	—	—
Rentsch et al. (2021)	P—cohort PW	68.2	93.4	4,297	—	3,627	—	-	670	67.8	42.8	10.5	15.2e
Rodriguez-Nava et al. (2021)	R—case control	68.0	58.1	313	—	175	—	91	21	70.9	44.7	—	78.9c
Shen et al. (2021)	R—cohort	64.0	49.3	525	—	120	—	—	405	37.3	17.7	10.5	15.1f
Shi et al., (2020)	R—cohort	69.0	64.3	42	—	21	—	—	21	30.1	19.0	—	100.0e
Tang et al. (2020)	R—case control	65.1	59.7	449	—	99	—	—	350	39.4	20.7	—	100.0f
Ugur et al. (2021)	R—cohort	50.6	54.2	1,251	253	—	—	—	998	—	—	—	—
Yormaz et al. (2020)	R—cohort	54.4	68.8	96	—	48	—	—	48	36.5	25.0	—	—
Yu et al. (2021)	R—cohort	61.8	57.3	973	—	764	—	165	—	44.8	46.5	6.5	29.6

ICU, intensive care unit; N/A, not applicable; P, prospective; PW, propensity weighted; R, retrospective.

^aDefined as mechanical ventilation/intubation.

^bDefined according to the World Health Organization 2020 Clinical management of severe acute respiratory infection (SARI) when COVID-19 disease is suspected, as temperature >38°, systolic blood pressure <100 mm Hg, heart rate >100 beats per minute, basal saturation less than 90%, respiratory rate >30 per minute, or altered level of consciousness.

^cDefined according to COVID-19 Treatment Guidelines Panel of the National Institutes of Health (SpO2 <94% on room air at sea level, PaO₂/FiO₂ <300 mmHg, RR > 30 bpm, or lung infiltrates >50%).

^dDefined as respiratory rate (RR) < 24/min, SO₂ < 92% or PaO₂/FiO₂ <300 mmHg.

^eDefined as any of the following: shortness of breath, RR ≥ 30 bpm; SO₂ ≤ 93% (at rest); PaO₂/FiO₂≤300 mmHg; pulmonary inflammation that progresses significantly within 24–48 h >50%.

^fSevere COVID-19 was defined according to the Diagnosis and Treatment Plan of COVID-19 suggested by National Health Commission of China (RR ≥ 30 breaths/min; SO₂ ≤ 93% at rest; PaO₂/FiO₂ ≤ 300 mm Hg.