Summary of findings 2. Anticoagulants compared to no treatment for people hospitalised with COVID‐19.

Anticoagulants compared to no treatment for people hospitalised with COVID‐19
Patient or population: people hospitalised with COVID‐19 Setting: hospital Intervention: anticoagulants (LMWH, UFH, fondaparinux, DOACs or VKA) Comparison: no treatment (no anticoagulants)
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with no treatment	Risk with anticoagulants
All‐cause mortality Follow‐up: from 15‐30 days	Study population		RR 0.64 (0.55 to 0.74)	8395 (3 observational studies)	⊕⊝⊝⊝ Very lowa,b	Anticoagulants may reduce all‐cause mortality but the evidence is very uncertain due to two study results being at critical and serious risk of bias. The numerical results are very unreliable for outcomes where critical risk of bias is an issue
	307 per 1000	196 per 1000 (169 to 227)
Necessity for additional respiratory support	No studies measured this outcome
Mortality related to COVID‐19	No studies measured this outcome
Deep vein thrombosis Follow‐up: up to 15 days	Study population		RR 5.67 (1.30 to 24.70)	1403 (1 observational study)	⊕⊝⊝⊝ Very lowc,d	It is uncertain if anticoagulants have any effect on DVT. The numerical results are very unreliable for outcomes where critical risk of bias is an issue.
	3 per 1000	19 per 1000 (4 to 82)
Pulmonary embolism Follow‐up: up to 15 days	Study population		RR 24.19 (3.31 to 176.53)	1403 (1 observational study)	⊕⊝⊝⊝ Very lowc,d	It is uncertain if anticoagulants have any effect on PE. The numerical results are very unreliable for outcomes where critical risk of bias is an issue.
	2 per 1000	40 per 1000 (5 to 292)
Major bleeding Follow‐up: from 15‐26 days	Study population		RR 1.19 (0.66 to 2.12)	7218 (2 observational studies)	⊕⊝⊝⊝ Very lowb,c,e	It is uncertain if anticoagulants have any effect on major bleeding. The numerical results are very unreliable for outcomes where critical risk of bias is an issue.
	19 per 1000	23 per 1000 (13 to 41)
Adverse events (minor bleeding)	No studies measured this outcome
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; COVID‐19: coronavirus disease 2019; DOACs: direct oral anticoagulants; DVT: deep vein thrombosis; LMWH: low‐molecular‐weight heparin; PE: pulmonary embolism; RR: risk ratio; UFH: unfractionated heparin; VKA: vitamin K antagonist
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.

^aDowngraded two levels due to study limitations. Overall critical/serious risk of bias in two studies, especially related to confounding.
^bDowngraded one level due to inconsistency. We found moderate unexplained heterogeneity (I² = 30% to 60%).
^cDowngraded one level due to study limitations. Overall critical risk of bias, especially related to confounding.
^dDowngraded two levels due to imprecision. Fewer than 300 events were included in the analysis and very large confidence interval.
^eDowngraded one level due to imprecision. Confidence interval of the absolute difference comprises both unimportant clinical harm and important clinical harm.