Summary of findings for the main comparison. LMWH compared to UFH for initial treatment of venous thromboembolism.

LMWH compared to UFH for initial treatment of venous thromboembolism
Patient or population: people with venous thromboembolism (VTE) Setting: hospital Intervention: Low molecular weight heparin (LMWH) Comparison: Unfractionated heparin (UFH)
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	№ of participants (studies)	Quality of the evidence (GRADE)	Comments
	Risk with UFH	Risk with LMWH
Incidence of recurrent VTE1 after initial treatment (up to 15 days)	Study population		OR 0.69 (0.49 to 0.98)	6238 (18 RCTs)	⊕⊕⊕⊝ MODERATE 2
	24 per 1000	17 per 1000 (12 to 24)
Incidence of recurrent VTE1 (3 months follow‐up)	Study population		OR 0.71 (0.56 to 0.90)	6661 (16 RCTs)	⊕⊕⊕⊝ MODERATE 3
	51 per 1000	37 per 1000 (29 to 46)
Incidence of recurrent VTE1 (end of follow‐up)	Study population		OR 0.72 (0.59 to 0.88)	9489 (22 RCTs)	⊕⊕⊕⊝ MODERATE 4
	50 per 1000	36 per 1000 (30 to 44)
Reduction in thrombus size (pre‐ and post‐treatment venograms) 5	Study population		OR 0.71 (0.61 to 0.82)	2909 (16 RCTs)	⊕⊕⊕⊝ LOW 6
	423 per 1000	342 per 1000 (309 to 375)
Incidence of major haemorrhagic episodes (during initial treatment ‐ up to 15 days) 7	Study population		OR 0.69 (0.50 to 0.95)	8780 (25 RCTs)	⊕⊕⊕⊝ MODERATE 8
	21 per 1000	15 per 1000 (11 to 20)
Overall mortality (end of follow‐up)	Study population		OR 0.84 (0.70 to 1.01)	9663 (24 RCTs)	⊕⊕⊕⊝ MODERATE 9
	57 per 1000	48 per 1000 (41 to 57)
*The basis for the assumed risk for 'study population' was the average risk in the comparison groups (i.e. total number of participants with events in the control group divided by the number of participants in the comparison group). 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; LMWH; low molecular weight heparin; RCTs; randomised controlled trials OR: Peto odds ratio; UFH: unfractionated heparin; VTE: venous thromboembolism
GRADE Working Group grades of evidence High quality: We are very confident that the true effect lies close to that of the estimate of the effect Moderate quality: 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 quality: Our confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect Very low quality: We have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of effect

¹ Recurrent venous thromboembolism (VTE) defined as recurrent deep vein thrombosis (DVT) or recurrent pulmonary embolism (PE). The diagnosis of recurrent DVT was accepted if one of the following criteria was met: (a) a new, constant intraluminal‐filling defect not present on the last available venogram; (b) if the venogram was not diagnostic either an abnormal 125I‐fibrinogen leg scan or abnormal impedance plethysmogram or ultrasound result, which had been normal before the suspected recurrent episode (Buller 1991). The diagnosis of PE was accepted if one of the following criteria was met: (a) a segmental defect on the perfusion lung scan that was unmatched on the ventilation scan or chest roentgenogram; (b) positive pulmonary angiography; (c) PE at autopsy.
 ² Downgraded as risk of bias serious due to high risk of attrition bias in 4 studies (Fiessinger 1996; Lindmarker 1994; Ninet 1991; Thery 1992), high risk of reporting bias in 2 studies (Lindmarker 1994; Pérez de Llano 2003) and high risk of other bias in 3 studies (Findik 2002; Harenberg 2000a; Lopaciuk 1992).
 ³ Downgraded as risk of bias serious due to high risk of attrition bias in 1 study (Breddin 2001), high risk of reporting bias in one study (Pérez de Llano 2003), and high risk of other bias in 2 studies (Findik 2002; Lopaciuk 1992).
 ⁴ Downgraded as risk of bias serious due to high risk of attrition bias in 2 studies (Breddin 2001; Lindmarker 1994), high risk of reporting bias in 2 studies (Lindmarker 1994; Pérez de Llano 2003), and high risk of other bias in 3 studies (Findik 2002; Harenberg 2000a; Lopaciuk 1992)
 ⁵ The number of participants in each group with an improved venographic score, if pre‐ and post‐treatment venograms were obtained and were assessed by persons unaware of treatment assignment.
 ⁶ Downgraded as risk of bias serious due to high risk of selection bias in 1 study (Luomanmaki 1996), high risk of attrition bias in 6 studies (Breddin 2001; Fiessinger 1996; Kakkar 2003; Lindmarker 1994; Ninet 1991; Thery 1992), high risk of reporting bias in 1 study (Lindmarker 1994), and high risk of other bias in 4 studies (Harenberg 2000a; Kakkar 2003; Lopaciuk 1992; Luomanmaki 1996). Downgraded further due to moderate heterogeneity (I² = 56%)
 ⁷ Haemorrhages were classified as major if they were intracranial, retroperitoneal, led directly to death, necessitated transfusion or they led to the interruption of antithrombotic treatment or (re)operation.
 ⁸ Downgraded as risk of bias serious due to high risk of selection bias in 1 study (Luomanmaki 1996), high risk of attrition bias in 5 studies (Fiessinger 1996; Kakkar 2003; Lindmarker 1994; Ninet 1991; Thery 1992), high risk of reporting bias in 2 studies (Lindmarker 1994; Pérez de Llano 2003), and high risk of other bias in 5 studies (Findik 2002; Harenberg 2000a; Kakkar 2003; Lopaciuk 1992; Luomanmaki 1996).
 ⁹ Downgraded as risk of bias serious due to high risk of selection bias in 1 study (Luomanmaki 1996), high risk of attrition bias in 4 studies (Breddin 2001; Kakkar 2003; Lindmarker 1994; Thery 1992), high risk of reporting bias in 2 studies (Lindmarker 1994; Pérez de Llano 2003), and high risk of other bias in 5 studies (Findik 2002; Harenberg 2000a; Kakkar 2003; Lopaciuk 1992; Luomanmaki 1996).